Wednesday.
1404.7130
XMM-Newton and Chandra cross calibration using HIFLUGCS galaxy clusters
Schellenberger, Reiprich, Lovisari, Nevalainen, David
Cosmo constraints from clusters rely on accurate gravitational mass estimates, which strongly depend on cluster gas temperature measurements. Therefore, systematic calibration difference may result in biased, instrument-dependent cosmological constraints. This is of special interest in the light of the tension between Planck results of the primary temperature anisotropies of the CMB and SZ plus X-ray cluster counts analyses. Quantify in detail the systematics and uncertainties of the cross-calibraton of the effective area between five X-ray instruments, EPICS-MOS1/MOS2/PN onboard XMM-Newtaon and ACIS-I/S onboard Chandra, and the influence on temperature measurements. Furthermore, assess the impact of the cross calibration uncertainties on cosmology. Using the HIFLUGCS sample, consisting of the 64 X-ray brightest galaxy clusters, constrain the ICM temperatures through spectral fitting int the same, mostly isothermal, regions and compare them. This work is an extension to a previous one using X-ray clusters by the IACHEC. Performing spectral fitting in the full energy band, find that best-fit temperatures determined with XMM-Newton/EPIC are significantly lower than Chandra/ACIS temperatures. Demonstrate that effects like multi temperature structure and different relative sensitivities of the instruments at certain energy bands cannot explain the observed differences. Conclude that using XMM-Newton/EPIC, instead of Chandra/ACIS to derive full energy band temperature profiles for cluster mass determination results in an 8% shift towards lower OmegaM values and <1% shift towards higher sigma8 values in a cosmological analysis of a complete sample of galaxy clusters. Such a shift is insufficient to significantly alleviate the tension between Planck CMB anisotropies and SZ plus XMM-Newton cosmological constraints.
1404.7144
The star formation histories of local group dwarf galaxies I. Hubble space telescope / wide field planetary camera 2 observations
Weisz, … Dalcanton, et al
Present uniformly measured SFHs of 50 LG dwarf galaxies based on color-magnitude diagram (CMD) analysis from archival Hubble imaging. SFHs can be recovered from CMDs that do not reach the oldest MS turn-off (MSTO), but the oldest MSTO is critical for precisely constraining the earliest epochs of SF. Find: (1) the average lifetime SFHs of dSphs can be approximated by an exponentially declining SFH with tau~5 Gyr; (2) the lower luminosity dSphs are less likely to have extended SFHs than more luminous dSphs; (3) the average SFHs of dIrrs, transition dwarfs (dTrans), and dwarf ellipticals (dEs) can be approximated by the combination of an exponentially declining SFH (tau~3-4 Gyr) for loopback ages >10-12 Gyr ago and a constant SFH thereafter; (4) the observed fraction of stellar mass formed prior to z=2 ranges considerably (80% for galaxies with M<1e5 Msun to 30% for galaxies with M>1e7 Msun) and is largely explained by environment; (5) the distinction between "ultra-faint" and "classical" dSphs is arbitrary; (6) LG dIrrs formed a significantly higher fraction of stellar mass prior to z=2 than the SDSS galaxies from Leiter 2012 and the SFHs from the abundance matching models of Behroozi+2013. This may indicate higher than expected SF efficiencies at early times in low mass galaxies. Finally, provide all the SFHs in tabulated electronic format.
Tuesday, April 29, 2014
Monday, April 28, 2014
Day 642
Tuesday.
1404.6524
Beyond halo mass: galactic conformity as a smoking gun of central galaxy assembly bias
Hearin, Watson, van den Bosch
Quenched central galaxies tend to reside in a preferentially quenched large-scale environment, a phenomenon that has been dubbed galactic conformity. This tendency persists out to scales far larger than the virial radius of the halo hosting the central. Therefore, conformity manifestly violates the widely adopted assumption that the DM halo mass Mvir exclusively governs galaxy occupation statistics. This paper is the first in the series studying the implications of the observed conformity signal for the galaxy-CM connection. Show that recent measurements of conformity on scales R~1-5 Mpc imply that central galaxy quenching statistics cannot be correctly predicted with the knowledge of Mvir alone. Also demonstrate that ejected (or 'backsplash') satellites cannot give rise to the signal. Then invoke the age matching model, which is predicated on the coevolution of galaxies and haloes. Find that this model pro dues a strong signal, and that central galaxies are solely responsible. Conclude that large-scale '2-halo' conformity represents a smoking gun of central galaxy assembly bias, and indicates that contemporary models of satellite quenching have systematically over-estimated the influence of post-infall processes.
1404.6527
Some like it triaxial: the universality of dark matter halo shapes and their evolution along the cosmic time
Despali, Giocoli, Tormen
Present a detailed analysis of DM halo shapes, studying how the distributions of ellipticity, prolateness and axial ratios evolve as a function of time and mass. With this purpose in mind, analyzed the results of three cosmological simulations, running an ellipsoidal halo finder to measure triaxial halo shapes. The simulations have different scales, mass limits and cosmological parameters, which allows to ensure a good resolution and statistics in a wide mass range, and to investigate the dependence of halo properties on the cosmological model. Confirm the tendency of haloes to be prolate at all times, even if they become more triaxial going to higher z. Regarding the dependence on mass, more massive haloes are also less spherical at all z, since they are the most recent forming systems and so still retain memory of their original shape at the moment of collapse. Then propose a rescaling of the shape-mass relations, using the variable nu=delta_c/sigma to represent the mass, which absorbs the dependence on both cosmology and time, allowing to find universal relations between halo masses and shape parameters (ellipticity, prolateness and the axial ratios) which hold at any redshift. This may be very useful to determine prior distributions of halo shapes for observational studies.
1404.6828
Galaxy and mass assembly (GAMA): the halo mass of galaxy groups from maximum-likelihood weak lensing
Han, Eke, Frnek, Mandelbaum, Norberg, Schneider, Peacock, … et al
Present maximum-likelihood WL analysis of the mass distribution in optically selected spectroscopic Galaxy Groups in GAMA, using SDSS photometric galaxies as sources. The scaling of halo mass, M_h, with various group observables is investigated. Main results: 1) the measured relations of halo mass with group luminosity, virial volume and central galaxy stellar mass, M*, agree very well with predictions from mock group catalogues constructed from a GALFORM SAM implemented in Millennium LCDM N-body sim, 2) the measured relations of halo mass with velocity dispersion and projected half-abundance radius show weak tension with mock predictions, hinting at problems in the mock galaxy dynamics and their small scale distribution; 3) the median Mh|M* measured from WL depends more sensitively on the dispersion in M* at fixed Mh than it does on the median M*|Mh. Measurements suggest an intrinsic dispersion of sigma_log(M*) ~ 0.15; 4) Comparing mass estimates with those in the catalogue, find that the group catalog mass can give biased results when used to select subsets of the group sample. Of the various new halo mass estimators that are calibrated using WL measurements, group luminosity is the best single-proxy estimator of group mass.
1404.6524
Beyond halo mass: galactic conformity as a smoking gun of central galaxy assembly bias
Hearin, Watson, van den Bosch
Quenched central galaxies tend to reside in a preferentially quenched large-scale environment, a phenomenon that has been dubbed galactic conformity. This tendency persists out to scales far larger than the virial radius of the halo hosting the central. Therefore, conformity manifestly violates the widely adopted assumption that the DM halo mass Mvir exclusively governs galaxy occupation statistics. This paper is the first in the series studying the implications of the observed conformity signal for the galaxy-CM connection. Show that recent measurements of conformity on scales R~1-5 Mpc imply that central galaxy quenching statistics cannot be correctly predicted with the knowledge of Mvir alone. Also demonstrate that ejected (or 'backsplash') satellites cannot give rise to the signal. Then invoke the age matching model, which is predicated on the coevolution of galaxies and haloes. Find that this model pro dues a strong signal, and that central galaxies are solely responsible. Conclude that large-scale '2-halo' conformity represents a smoking gun of central galaxy assembly bias, and indicates that contemporary models of satellite quenching have systematically over-estimated the influence of post-infall processes.
1404.6527
Some like it triaxial: the universality of dark matter halo shapes and their evolution along the cosmic time
Despali, Giocoli, Tormen
Present a detailed analysis of DM halo shapes, studying how the distributions of ellipticity, prolateness and axial ratios evolve as a function of time and mass. With this purpose in mind, analyzed the results of three cosmological simulations, running an ellipsoidal halo finder to measure triaxial halo shapes. The simulations have different scales, mass limits and cosmological parameters, which allows to ensure a good resolution and statistics in a wide mass range, and to investigate the dependence of halo properties on the cosmological model. Confirm the tendency of haloes to be prolate at all times, even if they become more triaxial going to higher z. Regarding the dependence on mass, more massive haloes are also less spherical at all z, since they are the most recent forming systems and so still retain memory of their original shape at the moment of collapse. Then propose a rescaling of the shape-mass relations, using the variable nu=delta_c/sigma to represent the mass, which absorbs the dependence on both cosmology and time, allowing to find universal relations between halo masses and shape parameters (ellipticity, prolateness and the axial ratios) which hold at any redshift. This may be very useful to determine prior distributions of halo shapes for observational studies.
1404.6828
Galaxy and mass assembly (GAMA): the halo mass of galaxy groups from maximum-likelihood weak lensing
Han, Eke, Frnek, Mandelbaum, Norberg, Schneider, Peacock, … et al
Present maximum-likelihood WL analysis of the mass distribution in optically selected spectroscopic Galaxy Groups in GAMA, using SDSS photometric galaxies as sources. The scaling of halo mass, M_h, with various group observables is investigated. Main results: 1) the measured relations of halo mass with group luminosity, virial volume and central galaxy stellar mass, M*, agree very well with predictions from mock group catalogues constructed from a GALFORM SAM implemented in Millennium LCDM N-body sim, 2) the measured relations of halo mass with velocity dispersion and projected half-abundance radius show weak tension with mock predictions, hinting at problems in the mock galaxy dynamics and their small scale distribution; 3) the median Mh|M* measured from WL depends more sensitively on the dispersion in M* at fixed Mh than it does on the median M*|Mh. Measurements suggest an intrinsic dispersion of sigma_log(M*) ~ 0.15; 4) Comparing mass estimates with those in the catalogue, find that the group catalog mass can give biased results when used to select subsets of the group sample. Of the various new halo mass estimators that are calibrated using WL measurements, group luminosity is the best single-proxy estimator of group mass.
Day 641
Monday.
1404.6250
The redshift evolution of the mean temperature, pressure, and entropy profiles in 80 SPT-selected galaxy clusters
McDonald, .. Vikhlinin, et al
80 clusters in 2500 deg2 SPT + Chandra observation. Divide into subsamples of ~20 clusters based on z and central density, performing an X-ray fit to all clusters in a subsample simultaneously, assuming self-similarity of the temperature profile. This approach allows to constrain the shape of the temperature profile over 0<r<1.5R500, which would be impossible on a per-cluster basis (individual clusters only have 2000 X-ray photon counts). Find that high-z (0.6<z<1.2) clusters are slightly (~40%) cooler both in the inner (r<0.1 R500) and outer (r>R500) regions than their low-z (0.3<z<0.6) counterparts. Combining the average temperature profile with measured gas density profiles from the earlier work, infer the average pressure and entropy profiles for each subsample. Overall, observed pressure profiles agree well with earlier lower-z measurements, suggesting minimal z evolution in the pressure profile outside of the core. Find no measurable z evolution in the entropy profile at r<0.7R500. Observe a slight flattening of the entropy profile at r>R5000 in the high-z subsample. This flattening is consistent with a temperature bias due to the enhanced (~3x) rate at which group-mass (~2 keV) halos, which would go undetected at the survey depth, are accreting onto the cluster at z~1. This work demonstrates a powerful method for inferring spatially-resolved cluster properties in the case where individual cluster signal-to-noise is low, but the number of observed clusters is high.
1404.6251
Overconsumption, outflows and the quenching of satellite galaxies
McGee, Bower, Balogh
The baryon cycle of galaxies is a dynamic process involving the intake, consumption and ejection of vast quantities of gas. In contrast, the conventional picture of satellite galaxies has them methodically turning a large gas reservoir into stars until this reservoir is forcibly removed due to external ram pressure---this picture needs revision. The modern understanding of the baryon cycle suggests that in some regimes the simple interruption of the fresh gas supply may quench satellite galaxies long before stripping events occur, a process dubbed "overconsumption". Compile measurement from the literature of observed satellite quenching times at a range of redshifts to determine if satellites are principally quenched through orbit-based gas stripping events -- either direct stripping of the disk (ram pressure) or the extended gas halo (strangulation) -- or from internally-driven SF outflows via overconsumption. The observed timescales show significant deviation from the evolution expected for gas stripping mechanisms and suggest that either ram pressure stripping is much more efficient at high z, or that secular outflows quench satellites before orbit-based stripping occurs. Given the strong z evolution of SFRs, at high z (>1.5) even moderate outflow rates will lead to extremely short quenching times with the expectation that such satellites will be quenched almost immediately following the cessation of cosmological inflow, regardless of stripping events. Observations of high z satellites give an indirect but sensitive measure of the outflow rate with current measurements suggesting that outflows are no larger than 2.5x the SFR for galaxies with a stellar mass of 1e10.5 Msun.
1404.6442
Sparse representation of photometric redshift PDFs: preparing for petascale astronomy
Kind, Brunner
Widespread adoption of photo-z PDFs. Both current and future photometric surveys are expected to obtain images of billions of distinct galaxies. As a result, storing and analyzing all of these PDFs will be non-trivial and even more severe if a survey plans to compute and store multiple different PDFs. In this paper, propose the use of a sparse basis representation to fully represent individual photo-z PDFs. By using an Orthogonal Matching Pursuit algorithm and a combination of Gaussian and Voigt basis functions, demonstrate how the approach is superior to a multi-Gaussian fitting, as approximately half of the parameters are required for the same fitting accuracy with the additional advantage that an entire PDF can be stored by using a 4-byte integer per basis function, and can achieve better accuracy by increasing the number of bases. By using data from CFHTLenS, demonstrate that only 10 to 20 points per galaxy are sufficient to reconstruct both the individual PDFs and the ensemble redshift distribution, N(z), to an accuracy of 99.9% when compared to the one built using the original PDFs computed with a resolution of delta z = 0.01, reducing the required storage of 200 original values by a a factor of 10 to 20. Finally, demonstrate how this basis representation can be directly extended to a cosmological analysis, thereby increasing computational performance without losing resolution nor accuracy.
1404.6458
The flux of kilogram-sized meteoroids from lunar impact monitoring
Suggs, Moser, Cooke, Suggs
The flashes from meteoroid impacts on the Moon are useful in determining the flux of impactors with masses as low as a few tens of grams. A routine monitoring program at NASA's Marshall Space Flight Center has recorded over 300 impacts since 2006. A selection of 126 flashes recorded during priers of photometric skies was analyzed, creating the largest and most homogeneous dataset of lunar impact flashes to date. Standard CCD photometric techniques were applied to the video and the luminous energy, kinetic energy, and mass are estimated for each impactor. Shower associations were determined for most of the impactors and a range of luminous efficiencies was considered. The flux to a limiting energy of 2.5e-6 kT TNT or 1.05e7 J is 1.03e-7 /km^2/hr and the flux to a limiting mass of 30g is 6.14e-10 /m^2/yr at the Moon. Comparison made with measurements and models of the meteoroid population indicate that the flux of objects in this size range is slightly lower (but within error bars) than flux at the size from the near Earth object and fireball population by Brown+2002. Size estimates for the crater detected by Lunar Reconnaissance Orbiter from a large impact observed on March 17, 2013 are also briefly discussed.
1404.6250
The redshift evolution of the mean temperature, pressure, and entropy profiles in 80 SPT-selected galaxy clusters
McDonald, .. Vikhlinin, et al
80 clusters in 2500 deg2 SPT + Chandra observation. Divide into subsamples of ~20 clusters based on z and central density, performing an X-ray fit to all clusters in a subsample simultaneously, assuming self-similarity of the temperature profile. This approach allows to constrain the shape of the temperature profile over 0<r<1.5R500, which would be impossible on a per-cluster basis (individual clusters only have 2000 X-ray photon counts). Find that high-z (0.6<z<1.2) clusters are slightly (~40%) cooler both in the inner (r<0.1 R500) and outer (r>R500) regions than their low-z (0.3<z<0.6) counterparts. Combining the average temperature profile with measured gas density profiles from the earlier work, infer the average pressure and entropy profiles for each subsample. Overall, observed pressure profiles agree well with earlier lower-z measurements, suggesting minimal z evolution in the pressure profile outside of the core. Find no measurable z evolution in the entropy profile at r<0.7R500. Observe a slight flattening of the entropy profile at r>R5000 in the high-z subsample. This flattening is consistent with a temperature bias due to the enhanced (~3x) rate at which group-mass (~2 keV) halos, which would go undetected at the survey depth, are accreting onto the cluster at z~1. This work demonstrates a powerful method for inferring spatially-resolved cluster properties in the case where individual cluster signal-to-noise is low, but the number of observed clusters is high.
1404.6251
Overconsumption, outflows and the quenching of satellite galaxies
McGee, Bower, Balogh
The baryon cycle of galaxies is a dynamic process involving the intake, consumption and ejection of vast quantities of gas. In contrast, the conventional picture of satellite galaxies has them methodically turning a large gas reservoir into stars until this reservoir is forcibly removed due to external ram pressure---this picture needs revision. The modern understanding of the baryon cycle suggests that in some regimes the simple interruption of the fresh gas supply may quench satellite galaxies long before stripping events occur, a process dubbed "overconsumption". Compile measurement from the literature of observed satellite quenching times at a range of redshifts to determine if satellites are principally quenched through orbit-based gas stripping events -- either direct stripping of the disk (ram pressure) or the extended gas halo (strangulation) -- or from internally-driven SF outflows via overconsumption. The observed timescales show significant deviation from the evolution expected for gas stripping mechanisms and suggest that either ram pressure stripping is much more efficient at high z, or that secular outflows quench satellites before orbit-based stripping occurs. Given the strong z evolution of SFRs, at high z (>1.5) even moderate outflow rates will lead to extremely short quenching times with the expectation that such satellites will be quenched almost immediately following the cessation of cosmological inflow, regardless of stripping events. Observations of high z satellites give an indirect but sensitive measure of the outflow rate with current measurements suggesting that outflows are no larger than 2.5x the SFR for galaxies with a stellar mass of 1e10.5 Msun.
1404.6442
Sparse representation of photometric redshift PDFs: preparing for petascale astronomy
Kind, Brunner
Widespread adoption of photo-z PDFs. Both current and future photometric surveys are expected to obtain images of billions of distinct galaxies. As a result, storing and analyzing all of these PDFs will be non-trivial and even more severe if a survey plans to compute and store multiple different PDFs. In this paper, propose the use of a sparse basis representation to fully represent individual photo-z PDFs. By using an Orthogonal Matching Pursuit algorithm and a combination of Gaussian and Voigt basis functions, demonstrate how the approach is superior to a multi-Gaussian fitting, as approximately half of the parameters are required for the same fitting accuracy with the additional advantage that an entire PDF can be stored by using a 4-byte integer per basis function, and can achieve better accuracy by increasing the number of bases. By using data from CFHTLenS, demonstrate that only 10 to 20 points per galaxy are sufficient to reconstruct both the individual PDFs and the ensemble redshift distribution, N(z), to an accuracy of 99.9% when compared to the one built using the original PDFs computed with a resolution of delta z = 0.01, reducing the required storage of 200 original values by a a factor of 10 to 20. Finally, demonstrate how this basis representation can be directly extended to a cosmological analysis, thereby increasing computational performance without losing resolution nor accuracy.
1404.6458
The flux of kilogram-sized meteoroids from lunar impact monitoring
Suggs, Moser, Cooke, Suggs
The flashes from meteoroid impacts on the Moon are useful in determining the flux of impactors with masses as low as a few tens of grams. A routine monitoring program at NASA's Marshall Space Flight Center has recorded over 300 impacts since 2006. A selection of 126 flashes recorded during priers of photometric skies was analyzed, creating the largest and most homogeneous dataset of lunar impact flashes to date. Standard CCD photometric techniques were applied to the video and the luminous energy, kinetic energy, and mass are estimated for each impactor. Shower associations were determined for most of the impactors and a range of luminous efficiencies was considered. The flux to a limiting energy of 2.5e-6 kT TNT or 1.05e7 J is 1.03e-7 /km^2/hr and the flux to a limiting mass of 30g is 6.14e-10 /m^2/yr at the Moon. Comparison made with measurements and models of the meteoroid population indicate that the flux of objects in this size range is slightly lower (but within error bars) than flux at the size from the near Earth object and fireball population by Brown+2002. Size estimates for the crater detected by Lunar Reconnaissance Orbiter from a large impact observed on March 17, 2013 are also briefly discussed.
Sunday, April 27, 2014
Day 640
Sunday.
1311.0139
Probing a dark matter density spike at the Galactic Center
Lacroix, Boehm, Silk
DM profile at the inner galaxy is uncertain, but important if we want to determine the gamma-ray and radio fluxes from DM annihilations. Use synchrotron emission to probe DM energy distribution in the inner galaxy. First solve the problem of the CR diffusion on very small scales (<1e-3 pc) by using a Green's function approach, and use this technique to quantify the effect of a spiky profile (rho(r)~r^{-7/3}) on the morphology and intensity of the synchrotron emission expected from DM. Illustrate results using 10 GeV and 800 GeV candidate weakly interacting DM particles annihilating directly into e+ e-. The critical assumptions are that the DM is heavier than a few GeV and directly produces a reasonable amount of electrons and positrons in the galaxy. Conclude that DM indirect detection techniques (including the Planck experiment) could be used to shed light on the DM halo profile on scales that lie beyond the capability of any current numerical simulations.
1401.5796
Chemodynamical evolution of the Milky Way disk II: variations with Galactic radius and height above the disk plane.
Minchev, Chiappini, Martig
Show that contamination by radial migration becomes more evident with increasing distance from the galactic center, because of the wider distribution of stellar birth radii for a given radial bin at z=0. As a result, the scatter in the age-metllaicity relation increase significantly as a function of galactic radius. Predict that the metallicity distributions of (unbiased) samples at different distances from the galactic center peak at approximately the same value, [Fe/H] ~ -0.15 dex, and have similar metal-poor tails extending to [Fe/H]~-1.3 dex. In contrast, the metal-rich tail decreases with increasing radius. Similarly, the [Mg/Fe] distribution always peaks at ~0.15 dex, but its low-end tail is lost as radius increases, while the high-end tails off at [Mg/Fe]~0.45 dex. This metal-rich, [alpha/Fe]-poor tail results from stars migrating outwards, which are always close to the disk plane. The reason for this is that migrators stay with cool kinematics, i.e., do not contribute to thick disk formation. Demonstrate that during mergers stars migrating outwards arrive significantly colder than the in-situ population. This has the important effect of working against disk flaring. The radial metallicity and [Mg/Fe] gradients in the model show significant variations with height above the plane due to changes in the mixture of stellar ages. An inversion in the radial metallicity gradient is found from negative to weakly positive and from positive to negative for the [Mg/Fe] gradient, with increasing distance from the disk plane. ...
1401.5799
Where do galaxies end?
Shull
Galaxies: systems of stars and gas embedded in extended haloes of DM, formed by infall of smaller systems at earlier times. True extend of a galaxy: virial radius (separation between collapsed structures in dynamical equilibrium and external infalling matter)? Gravitational radius, gas accretion radius, "galactopause" )arising from outflows that stall at 100-200 kpc over a range of outflow parameters and confining gas pressures)? Propose physical criteria to define bound structures, including a more realistic definition of R_vir (M*, M_h, z_a) for stellar mass M* and halo mass M_h, half of which formed at "assembly redshifts" z_a=0.7-1.3. Estimate the extent of bound gas and DM around L* galaxies to be ~200 kpc. The new virial radii, which mean R_vir~200 kpc, are 40-50% smaller than values estimated in HST/COS detections of H I and O VI absorbers around galaxies. In the new formalism, the MW stellar mass, log M*=10.7pm0.1, would correspond to R_vir=153(+25-16) kpc for half-mass halo assembly at z_a=1.06pm0.03. The frequency per unit redshift of low-redshift O VI absorption liens in QSO spectra suggests absorber sizes ~150 kpc when related to intervening 0.1 L* galaxies. This formalism is intended to clarify semantic differences arising from observations of extended gas in galactic haloes, circumgalactic medium (CGM), and filaments of the IGM. Astronomers should refer to bound gas in the galactic halo or GCM, and unbound gas as the CGM-IGM interface, on its way into the IGM.
1401.5800
CLASH-VLT: constraints on the Dark matter equation of state from accurate measurements of galaxy cluster mass profiles
Sartoris, … Borgani, Umetsu, Bartelmann, … Zitrin, … Broadhurst, Coe, … Melchior, et al
Constrain EoS from cluster galaxies (<<c, depends on gravitational potential only) with lensing (depends on gravitational potential plus the relativistic-pressure term that depends on cluster mass). Data: kinematic and lensing mass profiles of MACS 1206.2-0847 at z=0.44 from CLASH. Baryons contribute at most 15% to the total mass in clusters and their pressure is negligible, the EoS parameter describes the behavior of the DM fluid. Measure w=0.00 pm0.15 (stat) pm0.08 (syst), averaged over the radial range 0.5 Mpc <r<r200.
1401.5918
ESPRESSO: the next European exoplanet hunter
Pepe et al
ESPRESSO: Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations---the next VLT high resolution spectrograph. Forseen to gain 2 magus with respect to its predecessor HARPS, and to improve the instrumental radial-velocity precision to reach the 10 cm/s level. Operated with one or two Unit Telescopes (8.2m). Main scientific drivers: search and characterization of rocky exoplanets in the habitable zone of quiet, nearby G to M-dwards and the analysis of the variability of fundamental physical constants. Passed final design review in May 2013, entered the manufacturing phase, to be installed at Paranal Observatory in 2016; operation planned to start by the end of the same year.
1401.5945
A comet could not produce the carbon-14 spike in the 8the century
Usoskin, Kovaltsov
Increase in 14C ca. 775 AD recently found could be due to extreme solar energetic particle event [which would have produced auroras at low latitudes, which should have been recorded], or it could be due to a comet bringing additional 14C to Earth. Calculate a realistic mass and size of such a comet to show that it would have been huge (~100 mms across and 1e14-15 ton of mass) and would have produced a disastrous impact on Earth. Such an impact could not remain unnoticed in the geological records and chronicles. The absence of an evidence for such a dramatic event makes this hypothesis invalid.
1401.6018
Intrinsic alignments in the cross-correlation of cosmic shear and CMB weak lensing
Hall, Taylor
Demonstrate that the IA of galaxies with LS tidal fields sources an extra contribution to the recently-detected cross-correlation of galaxy shear and weak lensing of the microwave background. The extra term is the analogy of the 'GI' term in standard cosmic shear studies, and results in a reduction in the amplitude of the cross-correlation. Compute the IA contribution in linear and NL theory, and show that it can be at roughly the 15% level for CFHT Stripe 82 z distribution, if the canonical amplitude of IA is assumed. The new term can therefore potentially reconcile the apparently low value of the measured cross-correlation with standard LCDM. Discuss various small-scale effects in the signal and the dependence on the source z distribution. Discuss the exciting possibility of self-calibrating IA with a joint analysis of cosmic shear and WL of the microwave background.
1401.6137
The VIMOS public extragalactic redshift survey (VIPERS): a quiescent formation of massive red-sequence galaxies over the past 9 Gyr
Fritz et al
Evolution of CMR and LF at 0.4<z<1.3 from VIPERS using 45k galaxies with spectro-z down to i'_AB<22.5 over 10.32 deg2 in two fields. … Regardless of the method of selecting ETGs, measure a consistent evolution of the red-sequence: find a moderate evolution of the RS intercept of Delta(U-V)=0.28 pm 0.14 mag, favoring exponentially declining SF histories with SF truncation at 1.7<z<2.3. Together with the rise in the ETG number density by 0.64 dex since z=1, this suggests a rapid build-up of massive galaxies (M>1e11 Msun) and expeditious RS formation over a short period of ~1.5 Gyr starting before z=1. This is supported by the detection of ongoing SF in ETGs at 0.9<z<1.0, in contrast with the quiescent red stellar populations of ETGs at 0.5<z<0.6. There is an increase in the observed CMR scatter with redshift, two times larger than in galaxy clusters and at variance with theoretical models. Discuss possible physical mechanisms that support the observed evolution of the red galaxy population. Findings point out that the massive galaxies have experienced a sharp SF quenching at z~1 with only limited additional merging. In contrast, less-massive galaxies experience a mix of SF truncation and minor mergers which build-up the low- and intermediate-mass end of the CMR.
1311.0139
Probing a dark matter density spike at the Galactic Center
Lacroix, Boehm, Silk
DM profile at the inner galaxy is uncertain, but important if we want to determine the gamma-ray and radio fluxes from DM annihilations. Use synchrotron emission to probe DM energy distribution in the inner galaxy. First solve the problem of the CR diffusion on very small scales (<1e-3 pc) by using a Green's function approach, and use this technique to quantify the effect of a spiky profile (rho(r)~r^{-7/3}) on the morphology and intensity of the synchrotron emission expected from DM. Illustrate results using 10 GeV and 800 GeV candidate weakly interacting DM particles annihilating directly into e+ e-. The critical assumptions are that the DM is heavier than a few GeV and directly produces a reasonable amount of electrons and positrons in the galaxy. Conclude that DM indirect detection techniques (including the Planck experiment) could be used to shed light on the DM halo profile on scales that lie beyond the capability of any current numerical simulations.
1401.5796
Chemodynamical evolution of the Milky Way disk II: variations with Galactic radius and height above the disk plane.
Minchev, Chiappini, Martig
Show that contamination by radial migration becomes more evident with increasing distance from the galactic center, because of the wider distribution of stellar birth radii for a given radial bin at z=0. As a result, the scatter in the age-metllaicity relation increase significantly as a function of galactic radius. Predict that the metallicity distributions of (unbiased) samples at different distances from the galactic center peak at approximately the same value, [Fe/H] ~ -0.15 dex, and have similar metal-poor tails extending to [Fe/H]~-1.3 dex. In contrast, the metal-rich tail decreases with increasing radius. Similarly, the [Mg/Fe] distribution always peaks at ~0.15 dex, but its low-end tail is lost as radius increases, while the high-end tails off at [Mg/Fe]~0.45 dex. This metal-rich, [alpha/Fe]-poor tail results from stars migrating outwards, which are always close to the disk plane. The reason for this is that migrators stay with cool kinematics, i.e., do not contribute to thick disk formation. Demonstrate that during mergers stars migrating outwards arrive significantly colder than the in-situ population. This has the important effect of working against disk flaring. The radial metallicity and [Mg/Fe] gradients in the model show significant variations with height above the plane due to changes in the mixture of stellar ages. An inversion in the radial metallicity gradient is found from negative to weakly positive and from positive to negative for the [Mg/Fe] gradient, with increasing distance from the disk plane. ...
1401.5799
Where do galaxies end?
Shull
Galaxies: systems of stars and gas embedded in extended haloes of DM, formed by infall of smaller systems at earlier times. True extend of a galaxy: virial radius (separation between collapsed structures in dynamical equilibrium and external infalling matter)? Gravitational radius, gas accretion radius, "galactopause" )arising from outflows that stall at 100-200 kpc over a range of outflow parameters and confining gas pressures)? Propose physical criteria to define bound structures, including a more realistic definition of R_vir (M*, M_h, z_a) for stellar mass M* and halo mass M_h, half of which formed at "assembly redshifts" z_a=0.7-1.3. Estimate the extent of bound gas and DM around L* galaxies to be ~200 kpc. The new virial radii, which mean R_vir~200 kpc, are 40-50% smaller than values estimated in HST/COS detections of H I and O VI absorbers around galaxies. In the new formalism, the MW stellar mass, log M*=10.7pm0.1, would correspond to R_vir=153(+25-16) kpc for half-mass halo assembly at z_a=1.06pm0.03. The frequency per unit redshift of low-redshift O VI absorption liens in QSO spectra suggests absorber sizes ~150 kpc when related to intervening 0.1 L* galaxies. This formalism is intended to clarify semantic differences arising from observations of extended gas in galactic haloes, circumgalactic medium (CGM), and filaments of the IGM. Astronomers should refer to bound gas in the galactic halo or GCM, and unbound gas as the CGM-IGM interface, on its way into the IGM.
1401.5800
CLASH-VLT: constraints on the Dark matter equation of state from accurate measurements of galaxy cluster mass profiles
Sartoris, … Borgani, Umetsu, Bartelmann, … Zitrin, … Broadhurst, Coe, … Melchior, et al
Constrain EoS from cluster galaxies (<<c, depends on gravitational potential only) with lensing (depends on gravitational potential plus the relativistic-pressure term that depends on cluster mass). Data: kinematic and lensing mass profiles of MACS 1206.2-0847 at z=0.44 from CLASH. Baryons contribute at most 15% to the total mass in clusters and their pressure is negligible, the EoS parameter describes the behavior of the DM fluid. Measure w=0.00 pm0.15 (stat) pm0.08 (syst), averaged over the radial range 0.5 Mpc <r<r200.
1401.5918
ESPRESSO: the next European exoplanet hunter
Pepe et al
ESPRESSO: Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations---the next VLT high resolution spectrograph. Forseen to gain 2 magus with respect to its predecessor HARPS, and to improve the instrumental radial-velocity precision to reach the 10 cm/s level. Operated with one or two Unit Telescopes (8.2m). Main scientific drivers: search and characterization of rocky exoplanets in the habitable zone of quiet, nearby G to M-dwards and the analysis of the variability of fundamental physical constants. Passed final design review in May 2013, entered the manufacturing phase, to be installed at Paranal Observatory in 2016; operation planned to start by the end of the same year.
1401.5945
A comet could not produce the carbon-14 spike in the 8the century
Usoskin, Kovaltsov
Increase in 14C ca. 775 AD recently found could be due to extreme solar energetic particle event [which would have produced auroras at low latitudes, which should have been recorded], or it could be due to a comet bringing additional 14C to Earth. Calculate a realistic mass and size of such a comet to show that it would have been huge (~100 mms across and 1e14-15 ton of mass) and would have produced a disastrous impact on Earth. Such an impact could not remain unnoticed in the geological records and chronicles. The absence of an evidence for such a dramatic event makes this hypothesis invalid.
1401.6018
Intrinsic alignments in the cross-correlation of cosmic shear and CMB weak lensing
Hall, Taylor
Demonstrate that the IA of galaxies with LS tidal fields sources an extra contribution to the recently-detected cross-correlation of galaxy shear and weak lensing of the microwave background. The extra term is the analogy of the 'GI' term in standard cosmic shear studies, and results in a reduction in the amplitude of the cross-correlation. Compute the IA contribution in linear and NL theory, and show that it can be at roughly the 15% level for CFHT Stripe 82 z distribution, if the canonical amplitude of IA is assumed. The new term can therefore potentially reconcile the apparently low value of the measured cross-correlation with standard LCDM. Discuss various small-scale effects in the signal and the dependence on the source z distribution. Discuss the exciting possibility of self-calibrating IA with a joint analysis of cosmic shear and WL of the microwave background.
1401.6137
The VIMOS public extragalactic redshift survey (VIPERS): a quiescent formation of massive red-sequence galaxies over the past 9 Gyr
Fritz et al
Evolution of CMR and LF at 0.4<z<1.3 from VIPERS using 45k galaxies with spectro-z down to i'_AB<22.5 over 10.32 deg2 in two fields. … Regardless of the method of selecting ETGs, measure a consistent evolution of the red-sequence: find a moderate evolution of the RS intercept of Delta(U-V)=0.28 pm 0.14 mag, favoring exponentially declining SF histories with SF truncation at 1.7<z<2.3. Together with the rise in the ETG number density by 0.64 dex since z=1, this suggests a rapid build-up of massive galaxies (M>1e11 Msun) and expeditious RS formation over a short period of ~1.5 Gyr starting before z=1. This is supported by the detection of ongoing SF in ETGs at 0.9<z<1.0, in contrast with the quiescent red stellar populations of ETGs at 0.5<z<0.6. There is an increase in the observed CMR scatter with redshift, two times larger than in galaxy clusters and at variance with theoretical models. Discuss possible physical mechanisms that support the observed evolution of the red galaxy population. Findings point out that the massive galaxies have experienced a sharp SF quenching at z~1 with only limited additional merging. In contrast, less-massive galaxies experience a mix of SF truncation and minor mergers which build-up the low- and intermediate-mass end of the CMR.
Saturday, April 26, 2014
Day 639
Saturday.
1401.5466
The Zeldovich approximation
White
Zeldovich approximation for the growth of large-scale structure, which remains one of the most successful and insightful analytic models of structure formation. Use the Z approximation to compute the 2-pt function of the matter and biased tracers, and compare to the results of N-body simulations and other Lagrangian perturbation theories. Show that Lagrangian perturbation theories converge well and that the Z approximation provides a good fit to the N-body results except for the quadrupole moment of the halo correlation function. Extend the calculation of halo bias to 3rd order and also consider non-local biasing schemes, none of which remove the discrepancy. Argue that a part of the discrepancy owes to an incorrect prediction of inter-halo velocity correlations. Use the Z approximation to compute the ingredients of the Gaussian streaming model and show that this hybrid method provides a good fit to clustering of haloes in z space down to scales of tens of Mpc.
1401.5467
First results from the Dragonfly Telephoto Array: the apparent lack of a stellar halo in the massive spiral galaxy M101
Van Dokkum, Abraham, Merritt
A new telescope concept to study the low surface brightness outskirts of the spiral galaxy M101. The radial surface brightness profile is measured down to mu_g~32 mag/arcsec^2, a depth that approaches the sensitivity of star count studies in the Local Group. Convert surface brightness to surface mass density using the radial g-r color profile. The mass density profile shows no significant upturn at large radius and is well-approximated by a simple bulge + disk model out to R=70 kpc, corresponding to 18 disk scale lengths. Fitting a bulge+dusk+halo model find that the best-fitting halo mass M_halo ~ 1.7e8Msun. The total stellar mass of M101 is M_tot*, ~5.3e10Msun, and infer that the halo mass fraction f_halo = Mhalo/Mtot*~0.003 [? the mass of the "halo stars"?]. This mass fraction is lower than that of the MW (f_halo~0.02) and M31 (f_halo~0.04). All three galaxies fall below the f_halo - Mtot* relation predicted by recent cosmological sims that trace the light of disrupted satellites, with M101's halo mass a factor of ~10 below the median expectation. However, the predicted scatter in this relation is large, and more galaxies are needed to better quantify this possible tension with galaxy formation models. Dragonfly is well suited for this project: as integrated-light surface brightness is independent of distance, large numbers of galaxies can be studied in a uniform way.
1401.5472
Simultaneous modeling of the stellar and dust emission in distant galaxies: implications for star formation rate measurements
Utomo, Kriek, Labbe, Conroy, Fumagalli
Use NUV to MIR composite SEDs to simultaneously model the attenuated stellar and dust emission of 0.5<z<2.0 galaxies. These composite SEDs were previously constructed from the photometric catalogs of the NEWFIRM medium-band survey, by stacking the observed photometry of galaxies that have similar rest-fram NUV-to-NIR SEDs. In this work, include a stacked MIPS 24 um measurement for each SED type to extend the SEDs to rest-frame MIR wavelengths. Consistent with previous studies, the observed MIR emission for most SED types is higher than expected from only the attenuated stellar emission. Fit the NUV-to-MIR composite SEDs by the Flexible Stellar Population Synthesis (SPS) models, which include both stellar and dust emission. Compare the best-fit SFRs to the SFRs based on simple UV+IR estimators. The UV and IR luminosities overestimate SFRs - compared to the model SFRs - by more than ~1 dex for quiescent galaxies, while for the highest SF galaxies in the sample the two SFRs are broadly consistent. The difference in sSFRs also shows a gradually increasing trend with declining sSFR, implying that quiescent galaxies have even lower sSFRs than previously found. Contributions from evolved stellar populations to both the UV and the MIR SEDs most likely explain the discrepancy. Based on this work, conclude that SFRs should be determined from modeling the attenuated stellar and dust emission simultaneously, instead of employing simple UV+IR-based SFR estimators.
1401.5473
Ultra low surface brightness imaging with the Dragonfly telephoto array
Abraham, van Dokkum
Describe the Dragonfly Telephoto Array, a robotic imaging system optimized for the detection of extended ultra low surface brightness structures. The array consistent of 8 Canon 400mm f/2.8 telephoto lenses coupled to eight science-grade commercial CCD cameras. The lenses are mounted on a common framework and are co-aligned to image simultaneously the same position on the sky. The system provides an imaging capability equivalent to a 0.4m aperture f/1.0 refractor with a 2.6deg x 1.9deg FoV. The system has no obstructions in the light path, optimized baffling, and internal optical surfaces coated with a new generation of antireflection coatings based on sub-wavelength nano structures. As a result, the array's PSF has a factor of ~10 less scattered light at large radii than well-baffled reflecting telescopes. The DTA is capable of imaging extended structures to surface brightness levels below 30 mag/arcsec2 in 10h integrations (without binning or FG SF removal). This is considerably deeper than the surface brightness limit of any existing wide-field telescope. At present no systematic errors limiting the usefulness of much longer integration times has been identified. With longer integrations (50-100h), FG star removal and modest binning the DTA is capable of probing structures with surface brightnesses below 32 mag/arcsec2. Detection of structures at these surface brightness levels may hold the key to solving the missing substructure and missing satellite problems of inventional hierarchical galaxy formation models. The DTA is therefore executing a fully-automated multi-year imaging survey of a complete sample of nearby galaxies in order to undertake the first census of ultra-faint substructures in the nearby Universe.
1401.5578
Shaping the dust mass - star-formation rate relation
Hjorth, Gall, Michałowski
There is a remarkably tight relation between the observationally inferred dust masses and SFRs of SDSS galaxies, Mdust ~ SFR^1.11. Extend the relation to the high end and show that it bends over at very large SFRs (dust masses are lower than predicted for given SFR). Identify several distinct evolutionary processes in the diagram: (1) a star-bursting phase in which dust builds up rapidly at early times. The maximum attainable dust mass in this process is the case of the bend-over of the relation. A high dust-foramtion efficiency, a bottom-light IMF, and negligible SN shock dust destruction are required to produce sufficiently high dust masses. (2) A quiescent SF phase in which the subsequent parallel decline in dust mass and SFR gives rise to the Mdust-SFR relation, through astration [?] and dust destruction. The dust-go-gas ratio is approximately constant along the relation. Show that the power-law slpe of the Mdust-SFR relation is inversely proportional to the global Schmidt-Kennicutt law exponent (~0.9) in simple chemical evolution models. (3) A quenching phase which causes SF to drop while the dust mass stays roughly constant or drops proportionally. Combined with merging, these processes, as well as the range in total baryonic mass, give rise to a complex population of the diagram which adds significant scatter to the original Mdust-SFR relation. (4) At very high z, a population of galaxies located significantly below the local relation is predicted.
1401.5466
The Zeldovich approximation
White
Zeldovich approximation for the growth of large-scale structure, which remains one of the most successful and insightful analytic models of structure formation. Use the Z approximation to compute the 2-pt function of the matter and biased tracers, and compare to the results of N-body simulations and other Lagrangian perturbation theories. Show that Lagrangian perturbation theories converge well and that the Z approximation provides a good fit to the N-body results except for the quadrupole moment of the halo correlation function. Extend the calculation of halo bias to 3rd order and also consider non-local biasing schemes, none of which remove the discrepancy. Argue that a part of the discrepancy owes to an incorrect prediction of inter-halo velocity correlations. Use the Z approximation to compute the ingredients of the Gaussian streaming model and show that this hybrid method provides a good fit to clustering of haloes in z space down to scales of tens of Mpc.
1401.5467
First results from the Dragonfly Telephoto Array: the apparent lack of a stellar halo in the massive spiral galaxy M101
Van Dokkum, Abraham, Merritt
A new telescope concept to study the low surface brightness outskirts of the spiral galaxy M101. The radial surface brightness profile is measured down to mu_g~32 mag/arcsec^2, a depth that approaches the sensitivity of star count studies in the Local Group. Convert surface brightness to surface mass density using the radial g-r color profile. The mass density profile shows no significant upturn at large radius and is well-approximated by a simple bulge + disk model out to R=70 kpc, corresponding to 18 disk scale lengths. Fitting a bulge+dusk+halo model find that the best-fitting halo mass M_halo ~ 1.7e8Msun. The total stellar mass of M101 is M_tot*, ~5.3e10Msun, and infer that the halo mass fraction f_halo = Mhalo/Mtot*~0.003 [? the mass of the "halo stars"?]. This mass fraction is lower than that of the MW (f_halo~0.02) and M31 (f_halo~0.04). All three galaxies fall below the f_halo - Mtot* relation predicted by recent cosmological sims that trace the light of disrupted satellites, with M101's halo mass a factor of ~10 below the median expectation. However, the predicted scatter in this relation is large, and more galaxies are needed to better quantify this possible tension with galaxy formation models. Dragonfly is well suited for this project: as integrated-light surface brightness is independent of distance, large numbers of galaxies can be studied in a uniform way.
1401.5472
Simultaneous modeling of the stellar and dust emission in distant galaxies: implications for star formation rate measurements
Utomo, Kriek, Labbe, Conroy, Fumagalli
Use NUV to MIR composite SEDs to simultaneously model the attenuated stellar and dust emission of 0.5<z<2.0 galaxies. These composite SEDs were previously constructed from the photometric catalogs of the NEWFIRM medium-band survey, by stacking the observed photometry of galaxies that have similar rest-fram NUV-to-NIR SEDs. In this work, include a stacked MIPS 24 um measurement for each SED type to extend the SEDs to rest-frame MIR wavelengths. Consistent with previous studies, the observed MIR emission for most SED types is higher than expected from only the attenuated stellar emission. Fit the NUV-to-MIR composite SEDs by the Flexible Stellar Population Synthesis (SPS) models, which include both stellar and dust emission. Compare the best-fit SFRs to the SFRs based on simple UV+IR estimators. The UV and IR luminosities overestimate SFRs - compared to the model SFRs - by more than ~1 dex for quiescent galaxies, while for the highest SF galaxies in the sample the two SFRs are broadly consistent. The difference in sSFRs also shows a gradually increasing trend with declining sSFR, implying that quiescent galaxies have even lower sSFRs than previously found. Contributions from evolved stellar populations to both the UV and the MIR SEDs most likely explain the discrepancy. Based on this work, conclude that SFRs should be determined from modeling the attenuated stellar and dust emission simultaneously, instead of employing simple UV+IR-based SFR estimators.
1401.5473
Ultra low surface brightness imaging with the Dragonfly telephoto array
Abraham, van Dokkum
Describe the Dragonfly Telephoto Array, a robotic imaging system optimized for the detection of extended ultra low surface brightness structures. The array consistent of 8 Canon 400mm f/2.8 telephoto lenses coupled to eight science-grade commercial CCD cameras. The lenses are mounted on a common framework and are co-aligned to image simultaneously the same position on the sky. The system provides an imaging capability equivalent to a 0.4m aperture f/1.0 refractor with a 2.6deg x 1.9deg FoV. The system has no obstructions in the light path, optimized baffling, and internal optical surfaces coated with a new generation of antireflection coatings based on sub-wavelength nano structures. As a result, the array's PSF has a factor of ~10 less scattered light at large radii than well-baffled reflecting telescopes. The DTA is capable of imaging extended structures to surface brightness levels below 30 mag/arcsec2 in 10h integrations (without binning or FG SF removal). This is considerably deeper than the surface brightness limit of any existing wide-field telescope. At present no systematic errors limiting the usefulness of much longer integration times has been identified. With longer integrations (50-100h), FG star removal and modest binning the DTA is capable of probing structures with surface brightnesses below 32 mag/arcsec2. Detection of structures at these surface brightness levels may hold the key to solving the missing substructure and missing satellite problems of inventional hierarchical galaxy formation models. The DTA is therefore executing a fully-automated multi-year imaging survey of a complete sample of nearby galaxies in order to undertake the first census of ultra-faint substructures in the nearby Universe.
1401.5578
Shaping the dust mass - star-formation rate relation
Hjorth, Gall, Michałowski
There is a remarkably tight relation between the observationally inferred dust masses and SFRs of SDSS galaxies, Mdust ~ SFR^1.11. Extend the relation to the high end and show that it bends over at very large SFRs (dust masses are lower than predicted for given SFR). Identify several distinct evolutionary processes in the diagram: (1) a star-bursting phase in which dust builds up rapidly at early times. The maximum attainable dust mass in this process is the case of the bend-over of the relation. A high dust-foramtion efficiency, a bottom-light IMF, and negligible SN shock dust destruction are required to produce sufficiently high dust masses. (2) A quiescent SF phase in which the subsequent parallel decline in dust mass and SFR gives rise to the Mdust-SFR relation, through astration [?] and dust destruction. The dust-go-gas ratio is approximately constant along the relation. Show that the power-law slpe of the Mdust-SFR relation is inversely proportional to the global Schmidt-Kennicutt law exponent (~0.9) in simple chemical evolution models. (3) A quenching phase which causes SF to drop while the dust mass stays roughly constant or drops proportionally. Combined with merging, these processes, as well as the range in total baryonic mass, give rise to a complex population of the diagram which adds significant scatter to the original Mdust-SFR relation. (4) At very high z, a population of galaxies located significantly below the local relation is predicted.
Thursday, April 24, 2014
Day 638
Friday.
1003.1312 [that's weird]
Structure and dynamics of giant low surface brightness galaxies
Lelli, Fraternali, Sancisi
Ginat LSB galaxies are commonly thought to be massive, DM dominated systems. However, this conclusion is based on highly uncertain rotation curves. Present here a new study of two prototypical GLSB galaxies: Malin 1 and NGC 7589. Reanalyze existing HI observations and derived new rotation curves, which were used to investigate the distributions of luminous and DM in these galaxies. In contrast to previous findings, the rotation curves of both galaxies show a steep rise in the central parts, typical of high SB systems. Mass decompositions with a DM halo show that baryons may dominate the dynamics of the inner regions. Indeed, a "maximum disk" fit gives stellar M/L in the range of values typically find for HSB galaxies. These results, together with other recent studies, suggest that GLSB galaxies are systems with a double structure: an inner HSB early-type spiral galaxy and an outer LSB disk. Also tested the predictions of MOND: the rotation curve of NGC 7589 is reproduced well, whereas Malin 1 represents a challenging test for the theory.
1404.5959
A mass-dependenet density profile for DM haloes including the influence of galaxy formation
Di Cintio et al
Introduce a mass dependent density profile to describe the distribution of DM within galaxies, which takes into account the stellar-to-halo mass dependence of the response of DM to baryonic processes. The study is based on the analysis of hydrosim galaxies from dwarf to MW mass, drawn from the MaGICC project, which have been shown to match a wide range of disk scaling relationships. Find that the best fit parameters of a generic double power-law density profile vary in a systematic manner that depends on the stellar-to-halo mass ratio of each galaxy. Thus, the quantity Mstar/Mhalo constrains the inner (gamma) and outer (beta) slopes of DM density, and the sharpness of transition between the slopes (alpha), reducing the number of free parameters of the model to two. Due to the tight relation between stellar mass and halo mass, either of these quantities is sufficient to describe the DM halo profile including the effects of baryons. The concentration of the haloes in the Hydrosims is consistent with N-body expectations up to MW mass galaxies, at which mass the haloes become twice as concentrated as compared to pure DM runs. This mass dependent density profile can be directly applied to rotation curve data of observed galaxies and to semi analytic galaxy formation models as a significant improvement over the commonly used NFW profile.
1404.6014
Detection of the gravitational lens magnifying a type Ia supernova
Quimby, Oguri, et al
If a massive object warps space-time to form multiple images of a BG SNIa, a direct test of cosmic expansion is possible. However, these lensing events must first be distinguished from other rare phenomena. Report that a spectrum obtained of a SN (new type of super luminous SN or a normal SNIa magnified?) obtained after the SN faded away shows the presence of a FG galaxy -- the first found to strongly magnify a SNIa. Discuss how more lensed SNIa may be found than previously predicted.
1003.1312 [that's weird]
Structure and dynamics of giant low surface brightness galaxies
Lelli, Fraternali, Sancisi
Ginat LSB galaxies are commonly thought to be massive, DM dominated systems. However, this conclusion is based on highly uncertain rotation curves. Present here a new study of two prototypical GLSB galaxies: Malin 1 and NGC 7589. Reanalyze existing HI observations and derived new rotation curves, which were used to investigate the distributions of luminous and DM in these galaxies. In contrast to previous findings, the rotation curves of both galaxies show a steep rise in the central parts, typical of high SB systems. Mass decompositions with a DM halo show that baryons may dominate the dynamics of the inner regions. Indeed, a "maximum disk" fit gives stellar M/L in the range of values typically find for HSB galaxies. These results, together with other recent studies, suggest that GLSB galaxies are systems with a double structure: an inner HSB early-type spiral galaxy and an outer LSB disk. Also tested the predictions of MOND: the rotation curve of NGC 7589 is reproduced well, whereas Malin 1 represents a challenging test for the theory.
1404.5959
A mass-dependenet density profile for DM haloes including the influence of galaxy formation
Di Cintio et al
Introduce a mass dependent density profile to describe the distribution of DM within galaxies, which takes into account the stellar-to-halo mass dependence of the response of DM to baryonic processes. The study is based on the analysis of hydrosim galaxies from dwarf to MW mass, drawn from the MaGICC project, which have been shown to match a wide range of disk scaling relationships. Find that the best fit parameters of a generic double power-law density profile vary in a systematic manner that depends on the stellar-to-halo mass ratio of each galaxy. Thus, the quantity Mstar/Mhalo constrains the inner (gamma) and outer (beta) slopes of DM density, and the sharpness of transition between the slopes (alpha), reducing the number of free parameters of the model to two. Due to the tight relation between stellar mass and halo mass, either of these quantities is sufficient to describe the DM halo profile including the effects of baryons. The concentration of the haloes in the Hydrosims is consistent with N-body expectations up to MW mass galaxies, at which mass the haloes become twice as concentrated as compared to pure DM runs. This mass dependent density profile can be directly applied to rotation curve data of observed galaxies and to semi analytic galaxy formation models as a significant improvement over the commonly used NFW profile.
1404.6014
Detection of the gravitational lens magnifying a type Ia supernova
Quimby, Oguri, et al
If a massive object warps space-time to form multiple images of a BG SNIa, a direct test of cosmic expansion is possible. However, these lensing events must first be distinguished from other rare phenomena. Report that a spectrum obtained of a SN (new type of super luminous SN or a normal SNIa magnified?) obtained after the SN faded away shows the presence of a FG galaxy -- the first found to strongly magnify a SNIa. Discuss how more lensed SNIa may be found than previously predicted.
Wednesday, April 23, 2014
Day 637
Thursday.
1404.5618
A measurement of the Alcock-Paczynski test using cosmic voids in the SDSS
Sutter, Pisani, Wandelt
AP test on stacked cosmic voids in SDSS DR7 main sample, and DR10 LOWZ and CMASS samples. Find 1500 voids out to z=0.6. Assess the impact of peculiar velocities, use mock void catalogs, and found a constant uniform flattening of 14% along the LoS when peculiar velocities are included. This flattening appears universal for all void sizes at all z and for all tracer densities. Also use these mocks to identify an optical stacking strategy. After correcting for systematic effects, find that AP measurement leads to Omega_m~0.15 preferred over Omega_m~1.0 by likelihood ratio of 10. Find a factor of 4.5 preference of the likelihood ratio of LCDM Omega_m=0.3 model and a null measurement. Find substantial evidence for AP signal in the cosmic voids. Measurements with future surveys will provide tighter cosmo parameter constraints. The void-finding algorithm and catalogs used in this work is available on the web.
1404.5633
Dark matter-baryons separation at the lowest mass scale: the bullet group
Gastaldello et al
SL selected group of 2.4e14 Msun mass has a separation of 124 kpc between X-ray emitting collisional gas and the collision less galaxies and DM, traced by SL. DM interaction cross section limit of 10 cm^2/g. Lowest mass object found to date showing DM-baryon separation; detection of bullet-like objects is not rare and confined to mergers of massive objects; possible of a statistical detection of DM-baryons separation with future surveys.
1404.5636
The abundance of Bullet-groups in LCDM
Fernandez-Trincado et al
Estimate the expected distribution of displacements between DM-DM peaks and between DM-gas displacements in DM haloes with masses > 1e13 Msun/h. Find that 50% of the DM haloes with circular velocities in the range 300 km/s to 700 km/s (groups) show DM-DM displacements equal or larger than 186 kpc/h. For DM haloes with circular velocities larger than 700 km/s (clusters) this fraction rises to 70%. Find that 0.1 to 1.0% of the groups should present separations equal or larger than 87kpc/h; for clusters this fraction rises to 7pm3%, consistent with previous studies. Number density of groups similar to that observed above is~6e-7 Mpc^-3, 3x larger than the estimated value for clusters. These results open up the possibility for a new statistical test of LCDM by looking for DM-gas displacements in low mass clusters and groups.
1404.5624
Charting the evolution of the ages and metallicities of massive galaxies since z=0.7
Gallazzi, Bell, Zibetti, Brinchmann, Kelson
Perform deep, multi-object rest-frame optical spectroscopy with IMACS/Magellan of ~70 galaxies in the E-CDFS with 0.65<z<0.75, R>22.7 and M*>1e10 Msun. Constrain the stellar mass, mean stellar age and stellar metallicity of individual galaxies from stellar absorption features. Characterize for the first time the dependence of stellar metallicity and age on stellar mass at z~0.7 for all galaxies and for quiescent and SF galaxies separately. These relations for the whole sample have a similar shape as the z=0.1 SDSS analog, but are shifted by ~0.28 dex in age and by -0.13 dex in metallicity, at odds with simple passive evolution. Find that no additional SF and chemical enrichment are required for z=0.7 quiescent galaxies to evolve into the present-day quiescent population. However, this must be accompanied by the quenching of a fraction of z=0.7 M*>1e11 Msun SF galaxies with metallicities comparable to those of quiescent galaxies, thus increasing the scatter in age without affecting the metallicity distribution. However rapid quenching of the entire population of massive SF galaxies at z=0.7 would be inconsistent with the age/metallicity-mass relation for the population as a whole and with the metallicity distribution of SF galaxies only, which are on average 0.12 dex less metal-rich than their local counterparts. This indicates chemical enrichment until the present in at least a fraction of the z=0.7 massive SF galaxies.
1404.5618
A measurement of the Alcock-Paczynski test using cosmic voids in the SDSS
Sutter, Pisani, Wandelt
AP test on stacked cosmic voids in SDSS DR7 main sample, and DR10 LOWZ and CMASS samples. Find 1500 voids out to z=0.6. Assess the impact of peculiar velocities, use mock void catalogs, and found a constant uniform flattening of 14% along the LoS when peculiar velocities are included. This flattening appears universal for all void sizes at all z and for all tracer densities. Also use these mocks to identify an optical stacking strategy. After correcting for systematic effects, find that AP measurement leads to Omega_m~0.15 preferred over Omega_m~1.0 by likelihood ratio of 10. Find a factor of 4.5 preference of the likelihood ratio of LCDM Omega_m=0.3 model and a null measurement. Find substantial evidence for AP signal in the cosmic voids. Measurements with future surveys will provide tighter cosmo parameter constraints. The void-finding algorithm and catalogs used in this work is available on the web.
1404.5633
Dark matter-baryons separation at the lowest mass scale: the bullet group
Gastaldello et al
SL selected group of 2.4e14 Msun mass has a separation of 124 kpc between X-ray emitting collisional gas and the collision less galaxies and DM, traced by SL. DM interaction cross section limit of 10 cm^2/g. Lowest mass object found to date showing DM-baryon separation; detection of bullet-like objects is not rare and confined to mergers of massive objects; possible of a statistical detection of DM-baryons separation with future surveys.
1404.5636
The abundance of Bullet-groups in LCDM
Fernandez-Trincado et al
Estimate the expected distribution of displacements between DM-DM peaks and between DM-gas displacements in DM haloes with masses > 1e13 Msun/h. Find that 50% of the DM haloes with circular velocities in the range 300 km/s to 700 km/s (groups) show DM-DM displacements equal or larger than 186 kpc/h. For DM haloes with circular velocities larger than 700 km/s (clusters) this fraction rises to 70%. Find that 0.1 to 1.0% of the groups should present separations equal or larger than 87kpc/h; for clusters this fraction rises to 7pm3%, consistent with previous studies. Number density of groups similar to that observed above is~6e-7 Mpc^-3, 3x larger than the estimated value for clusters. These results open up the possibility for a new statistical test of LCDM by looking for DM-gas displacements in low mass clusters and groups.
1404.5624
Charting the evolution of the ages and metallicities of massive galaxies since z=0.7
Gallazzi, Bell, Zibetti, Brinchmann, Kelson
Perform deep, multi-object rest-frame optical spectroscopy with IMACS/Magellan of ~70 galaxies in the E-CDFS with 0.65<z<0.75, R>22.7 and M*>1e10 Msun. Constrain the stellar mass, mean stellar age and stellar metallicity of individual galaxies from stellar absorption features. Characterize for the first time the dependence of stellar metallicity and age on stellar mass at z~0.7 for all galaxies and for quiescent and SF galaxies separately. These relations for the whole sample have a similar shape as the z=0.1 SDSS analog, but are shifted by ~0.28 dex in age and by -0.13 dex in metallicity, at odds with simple passive evolution. Find that no additional SF and chemical enrichment are required for z=0.7 quiescent galaxies to evolve into the present-day quiescent population. However, this must be accompanied by the quenching of a fraction of z=0.7 M*>1e11 Msun SF galaxies with metallicities comparable to those of quiescent galaxies, thus increasing the scatter in age without affecting the metallicity distribution. However rapid quenching of the entire population of massive SF galaxies at z=0.7 would be inconsistent with the age/metallicity-mass relation for the population as a whole and with the metallicity distribution of SF galaxies only, which are on average 0.12 dex less metal-rich than their local counterparts. This indicates chemical enrichment until the present in at least a fraction of the z=0.7 massive SF galaxies.
Tuesday, April 22, 2014
Day 636
Wednesday.
1404.5299
A simple technique for predicting high-redshift galaxy evolution
Behroozi, Silk
Show that the ratio of galaxies' sSFRs to their host halos' specific mass accretion rates (SMARs) strongly constrains how the galaxies' stellar masses, sSFRs and those halo masses evolve over cosmic time. This evolutionary constraint provides a simple way to probe z>8 galaxy populations without direct observations. Tests of the method with galaxy properties at z=4 successfully reproduce the known evolution of the stellar mass-halo mass (SMHM) relation, galaxy sSFRs, and the cosmic SFR at z<4, the median galaxy mass at fixed halo mass increases strongly at z>4. Show that this result is closely linked to the flattening in galaxy sSFRs at z>2 compared to halo specific mass accretion rates; expect that average galaxy sSFRs at fixed stellar mass will continue their mild evolution to z~15. The expected cosmic SFR shows no breaks or features at z>8.5; this constrains both reionization and the possibility of a steep falloff in the CSFR at z=9-10. Finally, make predictions for the JWST, which should be able to observe one galaxy with M*>1e8 Msun per 1e3 Mpc^3 at z=9.6 and one such galaxy per 1e4 Mpc^3 at z=15.
1404.5301
The properties of the cool circumgalactic gas probed with the SDSS, WISE and GALEX surveys
Lan, Ménard, Zhu
Explore the distribution of cool (~1e4K) gas around galaxies and its dependence on galaxy properties. Cross-correlate 50k MgII absorbers with millions of sources from SDSS (optical), WISE (IR) and GALEX (UV) surveys, effectively extract about 2k galaxy-absorber paris at z~0.5 and probe relations between absorption strength and galaxy type, impact parameter and azimuthal angle. Find that cool gas traced by MgII absorbers exists around both SF and passive galaxies with a similar incidence rate on scales greater tan 100 kpc but each galaxy type exhibits a different behavior on smaller scales: MgII EW does not correlate with the presence of passive galaxies whereas stronger MgII absorbers tend to be found in the vicinity of SF galaxies. This effect is preferentially seen along the minor axis of these galaxies, suggesting that some of the gas is associated with outflowing material. In contrast, the distribution of cool gas around passive galaxies is consistent with being isotropic on the same scales. Quantify the average excess MgII EW as a function of galaxy properties and find propto SFR^0.6, sSFR^0.4 and M*^0.4 for SF galaxies. This work demonstrates that the dichotomy between SF and passive galaxies is reflected in the CGM traced by low-ionized gas. Also measure the covering fraction of MgII absorption and find it to be about 2-10x higher for SF galaxies than passive ones within 50 kpc. Estimate the amount of neutral gas in the halo of M*~1e10.8 Msun galaxies to be a few x1e9 Msun for both types of galaxies. Find that correlations between absorbers and sources detected in the UV and IR lead to physical trends consistent with those measured in the optical.
1404.5312
Constraining galaxy cluster temperatures and redshifts with eROSITA survey data
Borm, Reiprich, Mohammed, Lovisari
The upcoming eROSITA mission will exploit cluster mass function dependence on the DE by detecting roughly 100k clusters of galaxies in X-rays. For a precise cosmological analysis, the various galaxy cluster properties need to be measured with high precision and accuracy. To predict these characteristics of eROSITA galaxy clusters and to optimize optical follow-up observations, estimate the precision and the accuracy with which eROSITA will be able to determine galaxy cluster temperatures and redshifts from X-ray spectra. Additionally, present the total number of clusters for which these two properties will be available from the eROSITA survey directly. During its four years of all-sky surveys, eROSITA will determine cluster temperatures with relative uncertainties of Delta(T)/T<10% at the 68% CL for clusters up to z~0.16 which corresponds to ~1670 new clusters with precise properties. Z information itself will become available with a precision of Delta(z)/(1+z)<10% for clusters up to z~0.45. Additionally, estimate how the number of clusters with precise properties increases with a deepening of the exposure. Furthermore, the biases in the best-fit temperatures as well as in the estimated uncertainties are quantified and shown to be negligible in the relevant parameter range in general. For the remaining parameter sets, provide correction functions and factors. The eROSITA survey will increase the number of galaxy clusters with precise temperature measurements by a factor of 5-10. Thus the instrument present itself as a powerful tool for the determination of tight constraints on the cosmological parameters.
1404.5469
CFHTLenS: cosmological constraints from a combination of cosmic shear two-point and three-point correlations
Fu, Kilbinger, … et al
Higher-order, non-Gaussian aspects of the LSS carry valuable information on structure formation and cosmology, which is complementary to second-order statistics. In this work, measure second-and third-order WL aperture-mass moments from CFHTLenS and combine those with CMB anisotropy probes. The third moment is measured with a significance of 2 sigma. The combined constraint on Sigma_8=sigma_8(Omega_m/0.27)^a is improved by 10%, in comparison to 2nd order only, and the allowed ranges for Omega_m and sigma_8 are substantially reduced. Including general triangles of the lensing bispectrum yields tighter constraints compared to probing mainly equilateral triangles. Second and third-order CFHTLenS lensing measurements improve Planck CMB constraints on Omega_m and sigma_8 by 26% for flat LCDM. For a model with free curvature, the joint CFHTLenS-Planck result is Omega_m=0.28pm0.02 (68% CL), which is an improvement of 43% compared to Planck alone. Test how results are potentially subject to 3 astrophysical sources of contamination: source-lens clustering, the IA of galaxy shapes, and baryonic effects. Explore future limitations of the cosmological use of 3rd-order WL, such as the NL model and the Gaussianity of the likelihood function.
1404.5589
Model-independent measurements of cosmic expansion and growth at z=0.57 using the anisotropic clustering of CMASS galaxies from the Sloan Digital Sky Survey Data Release 9
Wang
Analyze 2DCF of CMASS galaxy sample from SDSS DR9 of the BOSS data. Modeling the 2DCF fully including NL effects and RSD in the scale of 30-120 Mpc/h, find H(0.57)r_s(z_d)/c = 0.0444pm0.0019, D_A(0.57)/r_s(z_d)=9.01pm0.23, and f_g(0.57) sigma_8(0.57)=0.474pm0.075, where r_s(z_d) is the sound horizon at the drag epoch computed using a simple integral, and f_g(z) is the growth rate at redshift z, and sigma_8(z) represents the matter power spectrum normalization on 8 Mpc/h scale at z. Find that the scales larger than 120 Mpc/h are dominated by noise in the 2DCF analysis, and that they inclusion of scales 30-40 Mpc/h significantly tightens the RSD measurement. Measurements are consistent with previous results using the same data, but have significantly better precision since they use all information from the 2DCF in the scale range of 30-120 Mpc/h. Measurements have been marginalized over sufficiently wide priors for the relevant parameters; they can be combined with other data to probe DE and gravity.
1404.5299
A simple technique for predicting high-redshift galaxy evolution
Behroozi, Silk
Show that the ratio of galaxies' sSFRs to their host halos' specific mass accretion rates (SMARs) strongly constrains how the galaxies' stellar masses, sSFRs and those halo masses evolve over cosmic time. This evolutionary constraint provides a simple way to probe z>8 galaxy populations without direct observations. Tests of the method with galaxy properties at z=4 successfully reproduce the known evolution of the stellar mass-halo mass (SMHM) relation, galaxy sSFRs, and the cosmic SFR at z<4, the median galaxy mass at fixed halo mass increases strongly at z>4. Show that this result is closely linked to the flattening in galaxy sSFRs at z>2 compared to halo specific mass accretion rates; expect that average galaxy sSFRs at fixed stellar mass will continue their mild evolution to z~15. The expected cosmic SFR shows no breaks or features at z>8.5; this constrains both reionization and the possibility of a steep falloff in the CSFR at z=9-10. Finally, make predictions for the JWST, which should be able to observe one galaxy with M*>1e8 Msun per 1e3 Mpc^3 at z=9.6 and one such galaxy per 1e4 Mpc^3 at z=15.
1404.5301
The properties of the cool circumgalactic gas probed with the SDSS, WISE and GALEX surveys
Lan, Ménard, Zhu
Explore the distribution of cool (~1e4K) gas around galaxies and its dependence on galaxy properties. Cross-correlate 50k MgII absorbers with millions of sources from SDSS (optical), WISE (IR) and GALEX (UV) surveys, effectively extract about 2k galaxy-absorber paris at z~0.5 and probe relations between absorption strength and galaxy type, impact parameter and azimuthal angle. Find that cool gas traced by MgII absorbers exists around both SF and passive galaxies with a similar incidence rate on scales greater tan 100 kpc but each galaxy type exhibits a different behavior on smaller scales: MgII EW does not correlate with the presence of passive galaxies whereas stronger MgII absorbers tend to be found in the vicinity of SF galaxies. This effect is preferentially seen along the minor axis of these galaxies, suggesting that some of the gas is associated with outflowing material. In contrast, the distribution of cool gas around passive galaxies is consistent with being isotropic on the same scales. Quantify the average excess MgII EW as a function of galaxy properties and find propto SFR^0.6, sSFR^0.4 and M*^0.4 for SF galaxies. This work demonstrates that the dichotomy between SF and passive galaxies is reflected in the CGM traced by low-ionized gas. Also measure the covering fraction of MgII absorption and find it to be about 2-10x higher for SF galaxies than passive ones within 50 kpc. Estimate the amount of neutral gas in the halo of M*~1e10.8 Msun galaxies to be a few x1e9 Msun for both types of galaxies. Find that correlations between absorbers and sources detected in the UV and IR lead to physical trends consistent with those measured in the optical.
1404.5312
Constraining galaxy cluster temperatures and redshifts with eROSITA survey data
Borm, Reiprich, Mohammed, Lovisari
The upcoming eROSITA mission will exploit cluster mass function dependence on the DE by detecting roughly 100k clusters of galaxies in X-rays. For a precise cosmological analysis, the various galaxy cluster properties need to be measured with high precision and accuracy. To predict these characteristics of eROSITA galaxy clusters and to optimize optical follow-up observations, estimate the precision and the accuracy with which eROSITA will be able to determine galaxy cluster temperatures and redshifts from X-ray spectra. Additionally, present the total number of clusters for which these two properties will be available from the eROSITA survey directly. During its four years of all-sky surveys, eROSITA will determine cluster temperatures with relative uncertainties of Delta(T)/T<10% at the 68% CL for clusters up to z~0.16 which corresponds to ~1670 new clusters with precise properties. Z information itself will become available with a precision of Delta(z)/(1+z)<10% for clusters up to z~0.45. Additionally, estimate how the number of clusters with precise properties increases with a deepening of the exposure. Furthermore, the biases in the best-fit temperatures as well as in the estimated uncertainties are quantified and shown to be negligible in the relevant parameter range in general. For the remaining parameter sets, provide correction functions and factors. The eROSITA survey will increase the number of galaxy clusters with precise temperature measurements by a factor of 5-10. Thus the instrument present itself as a powerful tool for the determination of tight constraints on the cosmological parameters.
1404.5469
CFHTLenS: cosmological constraints from a combination of cosmic shear two-point and three-point correlations
Fu, Kilbinger, … et al
Higher-order, non-Gaussian aspects of the LSS carry valuable information on structure formation and cosmology, which is complementary to second-order statistics. In this work, measure second-and third-order WL aperture-mass moments from CFHTLenS and combine those with CMB anisotropy probes. The third moment is measured with a significance of 2 sigma. The combined constraint on Sigma_8=sigma_8(Omega_m/0.27)^a is improved by 10%, in comparison to 2nd order only, and the allowed ranges for Omega_m and sigma_8 are substantially reduced. Including general triangles of the lensing bispectrum yields tighter constraints compared to probing mainly equilateral triangles. Second and third-order CFHTLenS lensing measurements improve Planck CMB constraints on Omega_m and sigma_8 by 26% for flat LCDM. For a model with free curvature, the joint CFHTLenS-Planck result is Omega_m=0.28pm0.02 (68% CL), which is an improvement of 43% compared to Planck alone. Test how results are potentially subject to 3 astrophysical sources of contamination: source-lens clustering, the IA of galaxy shapes, and baryonic effects. Explore future limitations of the cosmological use of 3rd-order WL, such as the NL model and the Gaussianity of the likelihood function.
1404.5589
Model-independent measurements of cosmic expansion and growth at z=0.57 using the anisotropic clustering of CMASS galaxies from the Sloan Digital Sky Survey Data Release 9
Wang
Analyze 2DCF of CMASS galaxy sample from SDSS DR9 of the BOSS data. Modeling the 2DCF fully including NL effects and RSD in the scale of 30-120 Mpc/h, find H(0.57)r_s(z_d)/c = 0.0444pm0.0019, D_A(0.57)/r_s(z_d)=9.01pm0.23, and f_g(0.57) sigma_8(0.57)=0.474pm0.075, where r_s(z_d) is the sound horizon at the drag epoch computed using a simple integral, and f_g(z) is the growth rate at redshift z, and sigma_8(z) represents the matter power spectrum normalization on 8 Mpc/h scale at z. Find that the scales larger than 120 Mpc/h are dominated by noise in the 2DCF analysis, and that they inclusion of scales 30-40 Mpc/h significantly tightens the RSD measurement. Measurements are consistent with previous results using the same data, but have significantly better precision since they use all information from the 2DCF in the scale range of 30-120 Mpc/h. Measurements have been marginalized over sufficiently wide priors for the relevant parameters; they can be combined with other data to probe DE and gravity.
Monday, April 21, 2014
Day 635
Tuesday.
1404.4870
Towards precision distances and 3d dust maps using broadband period-magnitude relations of RR Lyrae stars
Klein, Bloom
Determine the period-magnitude relations of RR Lyrae stars in 13 photometric bandpasses from 0.4 to 12 um using time series observations of 134 stars. The Bayesian formalism, extended from previous work to include the effects of LoS dust extinction, allows for the simultaneous inference of the posterior distribution of the mean absolute magnitude, slope of the period-magnitude power-law, and intrinsic scatter about a perfect power-law for each bandpass. In addition, the distance modulus and LoS dust extinction to each RR Lyrae star in the calibration sample is determined, yielding a sample median fractional distance error of 0.66%. The intrinsic scatter in all bands appears to be larger than the photometric errors, except in WISE W1 and W2 where the photometric error (sigma~0.05 mag) is to be comparable or larger that the intrinsic scatter. Additional observations at these wavelengths could improve the inferred distances to these sources further. As an application of the methodology, infer the distance to the RRc-type star RZCep at low Galactic latitude to be mu=8.0397pm0.0123 mag (405.4 pm 2.3 pc) with color excess E(B-V)=0.2461pm0.0089 mag. This distance, equivalent to a parallax of 2467pm14 microarcsec, is consistent with the published HST parallax measurement but with an uncertainty that is 13 times smaller than the HST measurement. If measurements (and methodology) hold up to scrutiny, the distances to these stars have been determined to an accuracy comparable to those expected with Gaia. As RR Lyrae are one of the primary components of the cosmic distance ladder, the achievement of sub-1% distance errors within a formalism that accounts for dust extinction may be considered a strong buttressing of the path to eventual 1% uncertainties in Hubble's constant.
1404.4874
ense cores in galaxies out to z=2.5 in SDSS, UltraVISTA, and the five 3d-HST/DANDELS fields: number density, evolution, and the apparent need for efficient cooling at high redshift
van Dokkum, et al
Ask when the dense galactic cores of massive galaxies formed, and determine how galaxies gradually assembled around them. Select galaxies that have a stellar mass 3e10 Msun inside r-1kpc out to z=2.5. The number density of galaxies with dense cores appears to have decreased from z=2.5 to the present, probably at least in part due to stellar mass loss and the resulting adiabatic expansion. Infer that dense cores were mostly formed at z>2.5, consistent with their largely quiescent stellar populations. While the cores appear to form early, the galaxies in which they reside show strong evolution: their total masses increase by a factor of 2-3from z=2.5 to 0 and their effective radii increase by a factor of 5-6. As a result, the contribution of dense cores to the total mass of the galaxies in which they reside decreases from ~50% at z=2.5 to ~15% at z=0. Because of their early formation, the contribution of dense cores to the total stellar mass budget of the Universe is a strong function of z. The stars in cores with M(1kpc)>3e10Msun make up ~0.1% of the stellar mass density of the Universe today but 10%-20% at z=2, depending on their IMF. The formation of these cores required the conversion of 1e11 Msun of gas into stars within 1 kpc, while preventing significant SF at larger radii.
1404.4870
Towards precision distances and 3d dust maps using broadband period-magnitude relations of RR Lyrae stars
Klein, Bloom
Determine the period-magnitude relations of RR Lyrae stars in 13 photometric bandpasses from 0.4 to 12 um using time series observations of 134 stars. The Bayesian formalism, extended from previous work to include the effects of LoS dust extinction, allows for the simultaneous inference of the posterior distribution of the mean absolute magnitude, slope of the period-magnitude power-law, and intrinsic scatter about a perfect power-law for each bandpass. In addition, the distance modulus and LoS dust extinction to each RR Lyrae star in the calibration sample is determined, yielding a sample median fractional distance error of 0.66%. The intrinsic scatter in all bands appears to be larger than the photometric errors, except in WISE W1 and W2 where the photometric error (sigma~0.05 mag) is to be comparable or larger that the intrinsic scatter. Additional observations at these wavelengths could improve the inferred distances to these sources further. As an application of the methodology, infer the distance to the RRc-type star RZCep at low Galactic latitude to be mu=8.0397pm0.0123 mag (405.4 pm 2.3 pc) with color excess E(B-V)=0.2461pm0.0089 mag. This distance, equivalent to a parallax of 2467pm14 microarcsec, is consistent with the published HST parallax measurement but with an uncertainty that is 13 times smaller than the HST measurement. If measurements (and methodology) hold up to scrutiny, the distances to these stars have been determined to an accuracy comparable to those expected with Gaia. As RR Lyrae are one of the primary components of the cosmic distance ladder, the achievement of sub-1% distance errors within a formalism that accounts for dust extinction may be considered a strong buttressing of the path to eventual 1% uncertainties in Hubble's constant.
1404.4874
ense cores in galaxies out to z=2.5 in SDSS, UltraVISTA, and the five 3d-HST/DANDELS fields: number density, evolution, and the apparent need for efficient cooling at high redshift
van Dokkum, et al
Ask when the dense galactic cores of massive galaxies formed, and determine how galaxies gradually assembled around them. Select galaxies that have a stellar mass 3e10 Msun inside r-1kpc out to z=2.5. The number density of galaxies with dense cores appears to have decreased from z=2.5 to the present, probably at least in part due to stellar mass loss and the resulting adiabatic expansion. Infer that dense cores were mostly formed at z>2.5, consistent with their largely quiescent stellar populations. While the cores appear to form early, the galaxies in which they reside show strong evolution: their total masses increase by a factor of 2-3from z=2.5 to 0 and their effective radii increase by a factor of 5-6. As a result, the contribution of dense cores to the total mass of the galaxies in which they reside decreases from ~50% at z=2.5 to ~15% at z=0. Because of their early formation, the contribution of dense cores to the total stellar mass budget of the Universe is a strong function of z. The stars in cores with M(1kpc)>3e10Msun make up ~0.1% of the stellar mass density of the Universe today but 10%-20% at z=2, depending on their IMF. The formation of these cores required the conversion of 1e11 Msun of gas into stars within 1 kpc, while preventing significant SF at larger radii.
Day 634
Easter Monday.
1404.4630
Formation of an embryonic supermassive star in the first galaxy
Inayoshi, Omukai, Tasker
Study gravitational collapse of ~8000K primordial gas cloud as a candidate progenitor for a supermassive star (SMS, >1e5 Msun) using a 3d hydrosim, including all the relevant cooling processes of both H2 and H, which can potentially induce cloud fragmentation. This is the first simulation of this kind to resolve protostar formation. Find that the cloud undergoes runaway collapse without a major episode of fragmentation. Although the H2 fraction jumps by a large factor via the 3 body reaction at 1e-13 g/cm3, its cooling remains inefficient due to the optical thickness, and the temperature remains >3000 K. When the central core of the cloud becomes opaque to continuum radiation at 1e-8 g/cm3, a hydrostatic protostar with ~0.2 Msun is formed. The protostar grows to mass ~1 Msun and radius ~2 AU within ~1 yr via rapid accretion of dense filamentary flows. WIth a high accretion rate ~ 2 Msun/yr, the protostar is expected to turn into a SMS within its lifetime, eventually collapsing to a seed for the SMBH observed in the early universe at z~7.
1404.4632
Line emitting galaxies beyond a redshift of 7: an improved method for estimating the evolving neutrality of the intergalactic medium
Schenker, Ellis, Konidaris, Stark
The z-dependent fraction of color-selected galaxies revealing Ly-a emission has become the most valuable constraint on the evolving neutrality of the early IGM. However, in addition to resonant scattering by neutral gas, the visibility of Ly-a is also dependent on the intrinsic properties of the host galaxy, including its stellar population, dust content and the nature of outflowing gas. Taking advantage of significant progress made in determining the line emitting properties of z~4-6 galaxies, propose an improved method, based on using the measured slopes of the rest-frame UV continua of galaxies, to interpret the growing body of NIR spectra of z>7 galaxies in order to take into account these host galaxy dependencies. In a first application of the new method, demonstrate its potential via a new spectroscopic survey of 7<z<8 galaxies undertaken with the Keck MOSFIRE spectrograph. Together with earlier published data, the data provides improved estimates of the evolving visibility of Lya, particularly at z~8. As a byproduct, also present a new line emitting galaxy at z~7.62 which supersedes an earlier z record. Discuss the improving constraints on the evolving neutral fraction over 6<z<8 and the implications for cosmic reionization.
1404.4808
Probing the diffuse braying distribution with the lensing-tSZ cross-correlation
Ma, Waerbeke, Hinshaw, Hojjati, Scott
Approximately half of the Universe's baryons are in a form that has been hard to detect directly. However, the missing component can be traced through the cross-correlation of the tSZ effect with WL. Build a model for this correlation and use it to constrain the extended baryon component, employing data from the CFHTLenS and Planck satellite. The measured correlation function is consistent with an isothermal beta-model for the halo gas pressure profile, and the 1- and 2-halo terms are both detected at the 4 sigma level. The effective virial temperature of the gas is found to be in the range 7e5-3e8K, with approximately 50 [%?] of the baryons appearing to lie beyond the virial radius of the halos, consistent with current expectations for the warm-hot IGM.
1404.4630
Formation of an embryonic supermassive star in the first galaxy
Inayoshi, Omukai, Tasker
Study gravitational collapse of ~8000K primordial gas cloud as a candidate progenitor for a supermassive star (SMS, >1e5 Msun) using a 3d hydrosim, including all the relevant cooling processes of both H2 and H, which can potentially induce cloud fragmentation. This is the first simulation of this kind to resolve protostar formation. Find that the cloud undergoes runaway collapse without a major episode of fragmentation. Although the H2 fraction jumps by a large factor via the 3 body reaction at 1e-13 g/cm3, its cooling remains inefficient due to the optical thickness, and the temperature remains >3000 K. When the central core of the cloud becomes opaque to continuum radiation at 1e-8 g/cm3, a hydrostatic protostar with ~0.2 Msun is formed. The protostar grows to mass ~1 Msun and radius ~2 AU within ~1 yr via rapid accretion of dense filamentary flows. WIth a high accretion rate ~ 2 Msun/yr, the protostar is expected to turn into a SMS within its lifetime, eventually collapsing to a seed for the SMBH observed in the early universe at z~7.
1404.4632
Line emitting galaxies beyond a redshift of 7: an improved method for estimating the evolving neutrality of the intergalactic medium
Schenker, Ellis, Konidaris, Stark
The z-dependent fraction of color-selected galaxies revealing Ly-a emission has become the most valuable constraint on the evolving neutrality of the early IGM. However, in addition to resonant scattering by neutral gas, the visibility of Ly-a is also dependent on the intrinsic properties of the host galaxy, including its stellar population, dust content and the nature of outflowing gas. Taking advantage of significant progress made in determining the line emitting properties of z~4-6 galaxies, propose an improved method, based on using the measured slopes of the rest-frame UV continua of galaxies, to interpret the growing body of NIR spectra of z>7 galaxies in order to take into account these host galaxy dependencies. In a first application of the new method, demonstrate its potential via a new spectroscopic survey of 7<z<8 galaxies undertaken with the Keck MOSFIRE spectrograph. Together with earlier published data, the data provides improved estimates of the evolving visibility of Lya, particularly at z~8. As a byproduct, also present a new line emitting galaxy at z~7.62 which supersedes an earlier z record. Discuss the improving constraints on the evolving neutral fraction over 6<z<8 and the implications for cosmic reionization.
1404.4808
Probing the diffuse braying distribution with the lensing-tSZ cross-correlation
Ma, Waerbeke, Hinshaw, Hojjati, Scott
Approximately half of the Universe's baryons are in a form that has been hard to detect directly. However, the missing component can be traced through the cross-correlation of the tSZ effect with WL. Build a model for this correlation and use it to constrain the extended baryon component, employing data from the CFHTLenS and Planck satellite. The measured correlation function is consistent with an isothermal beta-model for the halo gas pressure profile, and the 1- and 2-halo terms are both detected at the 4 sigma level. The effective virial temperature of the gas is found to be in the range 7e5-3e8K, with approximately 50 [%?] of the baryons appearing to lie beyond the virial radius of the halos, consistent with current expectations for the warm-hot IGM.
Saturday, April 19, 2014
Day 633
Sunday.
1401.5059
Establishing an analogue population for the most distant galaxies
Stanway, Davies
The LBGs at z~3 are more massive, luminous, redder, more extended and at higher metallicities than their z~5 counterparts. Thus extrapolations from the existing LBA (Lyman break analogue) samples (which match z=3 properties) have limited value for characterizing z>5 galaxies, or inferring properties unobservable at high z. Present a new pilot sample of 21 compact SF galaxies in the local 0.05<z<0.25 Universe, which are tuned to match the luminosities and SF volume densities observed in z>~5 LBGs. Analysis of optical emission line indices suggests that these sources have typical metallicities of a few tenths Solar. Present radio continuum observations of a subset of this sample (13 sources) and determine that their radio fluxes are consistent with those inferred form the UV, precluding the presence of a hazily obscured AGN or significant dusty SF.
1401.5063
The first hypervelocity star from the LAMOST survey
Zheng et al
B-type star with a heliocentric radial velocity about 620 km/s, which projects to a Galactocentric radial velocity component of ~477 km/s. With a heliocentric distance of ~13 kpc and an apparent magnitude of ~13 mag, it is the nearest and brightest HVS currently known. With a mass of ~9 Msun, similar to another massive HVS. The star is clustered on the sky with many other known HVSs, with the position suggesting a possible connection to Galactic center structures. With the currently poorly-determined proper motion, a Galactic enter origin of this HVS remains consistent with the data at the 2-3 sigma level. Discuss the potential of the LAMOST survey to discover a large statistical sample of HVSs of different types.
1401.5065
Photometric studies of Abell 1664: the subtle effect a minor merger has on cluster galaxies
Kleiner et al
A substructure ~800 kpc south of cluster core, identified as most likely the remnant core of a merging group which has passed pericenter and responsible for triggering a cold from in the cluster core. Find there are more asymmetric galaxies in the inner sample (~4 sigma) which is likely due to galaxy-galaxy interactions as the merging group passed through core passage. The color profiles of the galaxies are found to be consistent wit the morphology-density relation suggesting there is no unique environmental effect in A1664 that has enhanced galaxy transformations. This study favors the SF of cluster galaxies being quenched well before it is able to interact with the merging group, and demonstrates that a minor cluster merger has little effect on the observable parameters of cluster galaxies such as morphology and color.
1401.5067
Can AGN feedback break the self-similarity of galaxies, groups, and cluster?
Gaspari et al
Use high-res 3d hydrosims to isolate the impact of AGN feedback on the L_X-T_x relation, in the two archetypal and common regimes, self-regulated mechanical feedback and quasar thermal blast. Find that AGN feedback has severe difficulty in breaking the relation in a consistent way. The similarity breaking is directly linked to the gas evacuation within R_500, while the central cooling times are inversely proportional to the core density. Breaking self-similarity implies thus breaking the cool core, morphing all systems to non-cool-core objects, which is in clear contradiction with the observed data populated by several cool-core systems. Self-regulated feedback, which quenches cooling flows and preserves cool cores, prevents the dramatic evacuation and similarity breaking at any scale; the relation scatter is also limited. The impulsive thermal blast can weak the core-included LX-TX at T500<1 keV, but substantially empties and overheats the halo, generating a perennial non-cool-core group, as experienced by cosmo sims. Even with partial evacuation, massive systems remain overheated. Show the action of purely AGN feedback is to lower the luminosity and heating the gas, perpendicular to the fit.
1401.5073
First gravitational lensing mass estimate of a damped Lyman-alpha galaxy at z=2.2
Grillo, Fynbo
Galaxy at z=2.207 which is a damped Ly-a absorber and a deflector of a quasar at z=2.888. Impact parameter at 0.8pm0.1 kpc. QSO likely to be 2.2 mag brighter (or 8 times more luminous) than the median QSO at comparable redshifts. Describe the total mass distribution of the lens galaxy with a one-component singular isothermal sphere model and contrast the values of the observed and model-predicted magnification factors. Estimat that the effective velocity dispersion and 2d total mass, projected within a cylinder with radius equal to the impact parameter, are included between 60-170 km/s and 2.1e9-1.8e10 Msun, respectively. Remark that analysis of this kind are crucial to exploring the relation between the luminous and DM components of galaxies in the high-z universe.
1401.5059
Establishing an analogue population for the most distant galaxies
Stanway, Davies
The LBGs at z~3 are more massive, luminous, redder, more extended and at higher metallicities than their z~5 counterparts. Thus extrapolations from the existing LBA (Lyman break analogue) samples (which match z=3 properties) have limited value for characterizing z>5 galaxies, or inferring properties unobservable at high z. Present a new pilot sample of 21 compact SF galaxies in the local 0.05<z<0.25 Universe, which are tuned to match the luminosities and SF volume densities observed in z>~5 LBGs. Analysis of optical emission line indices suggests that these sources have typical metallicities of a few tenths Solar. Present radio continuum observations of a subset of this sample (13 sources) and determine that their radio fluxes are consistent with those inferred form the UV, precluding the presence of a hazily obscured AGN or significant dusty SF.
1401.5063
The first hypervelocity star from the LAMOST survey
Zheng et al
B-type star with a heliocentric radial velocity about 620 km/s, which projects to a Galactocentric radial velocity component of ~477 km/s. With a heliocentric distance of ~13 kpc and an apparent magnitude of ~13 mag, it is the nearest and brightest HVS currently known. With a mass of ~9 Msun, similar to another massive HVS. The star is clustered on the sky with many other known HVSs, with the position suggesting a possible connection to Galactic center structures. With the currently poorly-determined proper motion, a Galactic enter origin of this HVS remains consistent with the data at the 2-3 sigma level. Discuss the potential of the LAMOST survey to discover a large statistical sample of HVSs of different types.
1401.5065
Photometric studies of Abell 1664: the subtle effect a minor merger has on cluster galaxies
Kleiner et al
A substructure ~800 kpc south of cluster core, identified as most likely the remnant core of a merging group which has passed pericenter and responsible for triggering a cold from in the cluster core. Find there are more asymmetric galaxies in the inner sample (~4 sigma) which is likely due to galaxy-galaxy interactions as the merging group passed through core passage. The color profiles of the galaxies are found to be consistent wit the morphology-density relation suggesting there is no unique environmental effect in A1664 that has enhanced galaxy transformations. This study favors the SF of cluster galaxies being quenched well before it is able to interact with the merging group, and demonstrates that a minor cluster merger has little effect on the observable parameters of cluster galaxies such as morphology and color.
1401.5067
Can AGN feedback break the self-similarity of galaxies, groups, and cluster?
Gaspari et al
Use high-res 3d hydrosims to isolate the impact of AGN feedback on the L_X-T_x relation, in the two archetypal and common regimes, self-regulated mechanical feedback and quasar thermal blast. Find that AGN feedback has severe difficulty in breaking the relation in a consistent way. The similarity breaking is directly linked to the gas evacuation within R_500, while the central cooling times are inversely proportional to the core density. Breaking self-similarity implies thus breaking the cool core, morphing all systems to non-cool-core objects, which is in clear contradiction with the observed data populated by several cool-core systems. Self-regulated feedback, which quenches cooling flows and preserves cool cores, prevents the dramatic evacuation and similarity breaking at any scale; the relation scatter is also limited. The impulsive thermal blast can weak the core-included LX-TX at T500<1 keV, but substantially empties and overheats the halo, generating a perennial non-cool-core group, as experienced by cosmo sims. Even with partial evacuation, massive systems remain overheated. Show the action of purely AGN feedback is to lower the luminosity and heating the gas, perpendicular to the fit.
1401.5073
First gravitational lensing mass estimate of a damped Lyman-alpha galaxy at z=2.2
Grillo, Fynbo
Galaxy at z=2.207 which is a damped Ly-a absorber and a deflector of a quasar at z=2.888. Impact parameter at 0.8pm0.1 kpc. QSO likely to be 2.2 mag brighter (or 8 times more luminous) than the median QSO at comparable redshifts. Describe the total mass distribution of the lens galaxy with a one-component singular isothermal sphere model and contrast the values of the observed and model-predicted magnification factors. Estimat that the effective velocity dispersion and 2d total mass, projected within a cylinder with radius equal to the impact parameter, are included between 60-170 km/s and 2.1e9-1.8e10 Msun, respectively. Remark that analysis of this kind are crucial to exploring the relation between the luminous and DM components of galaxies in the high-z universe.
Friday, April 18, 2014
Day 632
Saturday.
1401.4459
An uncertainty principle for star formation. I. why galactic star formation relations break down below a certain spatial scale
Kruijssen, Longmore
Galactic scaling relations between the (surface densities of) the gas mass and the SFR are known to develop substantial scatter or even change form when considered below a certain spatial scale. Quantify how this behavior should be expected due to the incomplete statistical sampling of independent SF regions. Other included limiting factors are the incomplete sampling of SF tracers from the stellar IMF and the spatial drift between gas and stars. Present a simple uncertainty principle for SF, which can be used to predict and interpret the failure of galactic SF relations on small spatial scales. This uncertainty principle explains how the scatter of SF relations depends on the spatial scale and predicts a scale-dependent bias of the gas depletion time-scale when centering an aperture on gas or SF tracer peaks. Show how the scatter and bias are sensitive to the physical size and time-scales involved in the SF process (such as its duration or the molecular cloud lifetime), and illustrate how the formalism provides a powerful tool to constrain these largely unknown quantities. Thanks to its general form, the uncertainty principle can also be applied to other astrophysical systems, e.g. addressing the time-evolution of SF cores, protoplanetary discs, or galaxies and their nuclei.
1401.4503
Tracing the cosmic growth of super massive black holes to z~3 with Herschel
Delvecchio et al
Study a sample of Herschel-PACS selected galaxies within the GOODS-S and COSMOS fields in the framework of the PACS Evolutionary Probe (PEP) project. Starting from the rich multi-wavelength photometric data-sets available in both fields, perform a broad-band SED decomposition to disentangle the possible AGN contribution from that related to the host galaxy. Find that 37% of the sample shows signatures of nuclear activity at the 99% CL. The probability to reveal AGN activity increases for bright SF galaxies (>1e11 Lsun) at z0.3, becoming about 80% for the brightest (>1e12Lsun) IR galaxies at z>=1. Reconstruct the AGN bolometric LF and the SMBH growth rate across cosmic time up to z~3 from a FIR perspective. This work shows general agreement with most of the panchromatic estimates from the literature, with the global BH growth peaking at z~2 and reproducing the observed local BH mass density with consistent values of the radiative efficiency e_rad(~0.07).
1401.4459
An uncertainty principle for star formation. I. why galactic star formation relations break down below a certain spatial scale
Kruijssen, Longmore
Galactic scaling relations between the (surface densities of) the gas mass and the SFR are known to develop substantial scatter or even change form when considered below a certain spatial scale. Quantify how this behavior should be expected due to the incomplete statistical sampling of independent SF regions. Other included limiting factors are the incomplete sampling of SF tracers from the stellar IMF and the spatial drift between gas and stars. Present a simple uncertainty principle for SF, which can be used to predict and interpret the failure of galactic SF relations on small spatial scales. This uncertainty principle explains how the scatter of SF relations depends on the spatial scale and predicts a scale-dependent bias of the gas depletion time-scale when centering an aperture on gas or SF tracer peaks. Show how the scatter and bias are sensitive to the physical size and time-scales involved in the SF process (such as its duration or the molecular cloud lifetime), and illustrate how the formalism provides a powerful tool to constrain these largely unknown quantities. Thanks to its general form, the uncertainty principle can also be applied to other astrophysical systems, e.g. addressing the time-evolution of SF cores, protoplanetary discs, or galaxies and their nuclei.
1401.4503
Tracing the cosmic growth of super massive black holes to z~3 with Herschel
Delvecchio et al
Study a sample of Herschel-PACS selected galaxies within the GOODS-S and COSMOS fields in the framework of the PACS Evolutionary Probe (PEP) project. Starting from the rich multi-wavelength photometric data-sets available in both fields, perform a broad-band SED decomposition to disentangle the possible AGN contribution from that related to the host galaxy. Find that 37% of the sample shows signatures of nuclear activity at the 99% CL. The probability to reveal AGN activity increases for bright SF galaxies (>1e11 Lsun) at z0.3, becoming about 80% for the brightest (>1e12Lsun) IR galaxies at z>=1. Reconstruct the AGN bolometric LF and the SMBH growth rate across cosmic time up to z~3 from a FIR perspective. This work shows general agreement with most of the panchromatic estimates from the literature, with the global BH growth peaking at z~2 and reproducing the observed local BH mass density with consistent values of the radiative efficiency e_rad(~0.07).
Day 631
Friday.
1404.1899
Fingerprints of galactic loop I on the cosmic microwave background
Liu, Mertsch, Sarkar
Investigate possible imprints of galactic FG structures such as the 'radio loops' in the derived maps of the CMB. There is evidence for these not only at radio frequencies through their synchrotron radiation, but also at microwave frequencies where emission by dust dominates. This suggests the mechanism is magnetic dipole radiation from dust grains enriched by metallic iron, or ferrimagnetic molecules. This new FG identified is present at high galactic latitudes, and potentially dominates over the expected B-mode polarization signal due to primordial gravitational waves from inflation.
Science, 18 Apr 2014
An Earth-sized planet in the habitable zone of a cool star
Quintana et al
Although planets that are Earth-sized and smaller have been detected, these planets reside in orbits that are too close to their host star to allow liquid water on their surfaces. Present the detection of Kepler-186f, a 1.11pm0.14 Earth-radius planet that is the outermost of five planets, all roughly Earth-sized, that transit a 0.47pm0.05 solar-radius star. The intensity and spectrum of the star's radiation place Kepler-186f in the stellar habitable zone, implying that if Kepler-186f has an Earth-like atmosphere and water at its surface, then some of this water is likely to be in liquid form.
1404.4365
Stars get dizzy after lunch
Zhang, Penev
The tidal distraction of hot jupiters: because the planet's orbital angular momenta are a significant fraction of their stars' rotational angular momenta, they spin up their stars significantly while spiral lying to their deaths. It may be possible to search for tidally-destroyed planets by looking for stars with extremely short rotational periods, then looking for remnant planet cores around those candidates, anomalies in the malt distribution, or other signatures of the recent accretion of the planet.
1404.4368
Formation, tidal evolution and habitability of the Kepler-186 system
Bolmont et al
The Kepler 186 system consists of 5 planets orbiting an early-M dwarf. These planets have physical radii of 1.0-1.5 R_Earth and orbital periods of 4 to 130 days. The 1.1 R_Earth Kepler-186f with a period of 130 days is of particular interest. Its insolation of roughly 0.32 S_sun places it within the liquid water habitable zone. Present a multi-faceted study of the system. First show that the distribution of planet masses can be roughly reproduced if the planets accreted from a high-surface density disk presumably sculpted by an earlier phase of migration. However, simulations predict the existence of 1-2 undetected planets between planets e and f. Present a dynamical analysis of the system including the effect of tides. The timescale for tidal evolution is short enough that the four inner planets must have small obliquities and near-synchronous rotation rates. Tidal evolution of Kepler-186f is slow enough that its current spin state depends on a combination of its dissipation rate and the stellar age. Finally, study the habitability of Kepler-186f with a 1-d clement mode. The planet's surface temperature can be raised above 273K with 0.5-5 bars of CO2, depending on the amount of N2 present. Kepler-186f represents a case study of an Earth-sized planet in the cooler regions of the habitable zone of a cool star.
1404.4379
KOI-3278: a self-lensing binary star system
Kruse, Agol
Over 40% of sun-like stars are bound in binary or multistar systems. Stellar remnants in edge-on binary systems can gravitationally magnify their companions, as predicted 40 years ago. From Kepler, report the detection of such a "self-lensing" system, in which a 5-hr pulse of 0.1% amplitude occurs every orbital period. The WD stellar remnant and its Sun-like companion orbit one other very 88.18 days, a long period for a WD-eclipsing binary. By modeling the pulse as gravitational magnification (microlensing) long with Kepler's laws and stellar models, constrain the mass of the WD to be ~63% of the mass of the Sun. Further study of this system, and any other discovered like it, will help to constrain the physics of WDs and binary star evolution.
1404.4521
Detection of galaxies with Gaia
de Souza, et al
Gaia mission will also observe a large number of galaxies. In this work, intend to evaluate the number and the characteristics of the galaxies that will effectively pass the onboard selection algorithm of Gaia. Detection of objects in Gaia will be performed in a section of the focal plane known as the Sky Mapper. Taking into account the Video Procession Algorithm criterion of detection and considering the known light profiles of discs and bulge galaxies assess the number and the type of extra-galactic objects that will be observed by Gaia. Show that the stellar disk population of galaxies will be very difficult to observe. On the contrary the spheroidal component of elliptical galaxies and bulges having higher central surface brightness and steeper brightness profile will be more easy to be detected. Estimate that most of the 20k elliptical population of nearby galaxies inside the local region up to 170 Mpc are in condition to be observed by Gaia. A similar number of bulges could also be observed although the low luminosity bulges should escape detection. About two thirds of the more distant objects up to 600 Mpc could also be detected increasing the total sample to half a million objects including ellipticals and bulges. The angular size of the detected objects will never exceed 4.72 arc sec which is the size of the largest transmitted windows. An heterogeneous population of elliptical galaxies and bulges will be observable by Gaia. This nearby Universe sample of galaxies should constitute a very rich and ingesting sample to study their structural properties and their distribution.
1404.1899
Fingerprints of galactic loop I on the cosmic microwave background
Liu, Mertsch, Sarkar
Investigate possible imprints of galactic FG structures such as the 'radio loops' in the derived maps of the CMB. There is evidence for these not only at radio frequencies through their synchrotron radiation, but also at microwave frequencies where emission by dust dominates. This suggests the mechanism is magnetic dipole radiation from dust grains enriched by metallic iron, or ferrimagnetic molecules. This new FG identified is present at high galactic latitudes, and potentially dominates over the expected B-mode polarization signal due to primordial gravitational waves from inflation.
Science, 18 Apr 2014
An Earth-sized planet in the habitable zone of a cool star
Quintana et al
Although planets that are Earth-sized and smaller have been detected, these planets reside in orbits that are too close to their host star to allow liquid water on their surfaces. Present the detection of Kepler-186f, a 1.11pm0.14 Earth-radius planet that is the outermost of five planets, all roughly Earth-sized, that transit a 0.47pm0.05 solar-radius star. The intensity and spectrum of the star's radiation place Kepler-186f in the stellar habitable zone, implying that if Kepler-186f has an Earth-like atmosphere and water at its surface, then some of this water is likely to be in liquid form.
1404.4365
Stars get dizzy after lunch
Zhang, Penev
The tidal distraction of hot jupiters: because the planet's orbital angular momenta are a significant fraction of their stars' rotational angular momenta, they spin up their stars significantly while spiral lying to their deaths. It may be possible to search for tidally-destroyed planets by looking for stars with extremely short rotational periods, then looking for remnant planet cores around those candidates, anomalies in the malt distribution, or other signatures of the recent accretion of the planet.
1404.4368
Formation, tidal evolution and habitability of the Kepler-186 system
Bolmont et al
The Kepler 186 system consists of 5 planets orbiting an early-M dwarf. These planets have physical radii of 1.0-1.5 R_Earth and orbital periods of 4 to 130 days. The 1.1 R_Earth Kepler-186f with a period of 130 days is of particular interest. Its insolation of roughly 0.32 S_sun places it within the liquid water habitable zone. Present a multi-faceted study of the system. First show that the distribution of planet masses can be roughly reproduced if the planets accreted from a high-surface density disk presumably sculpted by an earlier phase of migration. However, simulations predict the existence of 1-2 undetected planets between planets e and f. Present a dynamical analysis of the system including the effect of tides. The timescale for tidal evolution is short enough that the four inner planets must have small obliquities and near-synchronous rotation rates. Tidal evolution of Kepler-186f is slow enough that its current spin state depends on a combination of its dissipation rate and the stellar age. Finally, study the habitability of Kepler-186f with a 1-d clement mode. The planet's surface temperature can be raised above 273K with 0.5-5 bars of CO2, depending on the amount of N2 present. Kepler-186f represents a case study of an Earth-sized planet in the cooler regions of the habitable zone of a cool star.
1404.4379
KOI-3278: a self-lensing binary star system
Kruse, Agol
Over 40% of sun-like stars are bound in binary or multistar systems. Stellar remnants in edge-on binary systems can gravitationally magnify their companions, as predicted 40 years ago. From Kepler, report the detection of such a "self-lensing" system, in which a 5-hr pulse of 0.1% amplitude occurs every orbital period. The WD stellar remnant and its Sun-like companion orbit one other very 88.18 days, a long period for a WD-eclipsing binary. By modeling the pulse as gravitational magnification (microlensing) long with Kepler's laws and stellar models, constrain the mass of the WD to be ~63% of the mass of the Sun. Further study of this system, and any other discovered like it, will help to constrain the physics of WDs and binary star evolution.
1404.4521
Detection of galaxies with Gaia
de Souza, et al
Gaia mission will also observe a large number of galaxies. In this work, intend to evaluate the number and the characteristics of the galaxies that will effectively pass the onboard selection algorithm of Gaia. Detection of objects in Gaia will be performed in a section of the focal plane known as the Sky Mapper. Taking into account the Video Procession Algorithm criterion of detection and considering the known light profiles of discs and bulge galaxies assess the number and the type of extra-galactic objects that will be observed by Gaia. Show that the stellar disk population of galaxies will be very difficult to observe. On the contrary the spheroidal component of elliptical galaxies and bulges having higher central surface brightness and steeper brightness profile will be more easy to be detected. Estimate that most of the 20k elliptical population of nearby galaxies inside the local region up to 170 Mpc are in condition to be observed by Gaia. A similar number of bulges could also be observed although the low luminosity bulges should escape detection. About two thirds of the more distant objects up to 600 Mpc could also be detected increasing the total sample to half a million objects including ellipticals and bulges. The angular size of the detected objects will never exceed 4.72 arc sec which is the size of the largest transmitted windows. An heterogeneous population of elliptical galaxies and bulges will be observable by Gaia. This nearby Universe sample of galaxies should constitute a very rich and ingesting sample to study their structural properties and their distribution.
Thursday, April 17, 2014
Day 630
Thursday.
1404.4049
A census of the expected properties of classical Milky Way dwarfs in Milgomian dynamics
Lüghausen, Famaey, Kroupa
Revisit the classical MW dwarf spherical satellites Draco, Sculptor, Sextans, Carina, and Fornax in the framework of MOND, following the successful predictions of Andromeda's satellite galaxies. Use a Poisson solver with adaptive mesh refinement in order to account simultaneously for the gravitational influence of the MW and its satellites. This allows to rigorously model the important external field effect (EFE) of MOND, which can reduce the effective acceleration significantly. Make predictions on the M_dyn/L expected to be measured by an observer who assumes Newtonian dynamics to be valid. Show that MIlgromian dynamics predicts typical M_dyn/L~10…50 Msun/Lsun. The results for the most luminous ons, Fornax and Sculptor, agree well with available velocity dispersion data. The central power law slopes of the dynamical masses agrees exceedingly well with values inferred observationally from velocity dispersion measurements. The results for Sextans, Carina and Draco are low compared to usually quoted observational estimates, as already pointed out by Angus (2008). For MOND to survive further observational tests in these objects, one would need that either a) previous observational findings based on velocity dispersion measurements have overestimated the dynamical mass due to e.g., binaries and contaminant outliers, b) the satellites are not in virial equilibrium due to the MW tidal field, or c) the specific theory used here does not describe the EFE correctly (e.g., the EFE could be practically negligible in some other theories), or a combination of the three.
1404.4053
Where do galaxies end? a study of hydrodynamic-simulation galaxies and their integrated properties
Stevens, Martig, Croton, Feng
In Hydrosims, often a spherical aperture defines the boundary between the galaxy and the rest of its parent (sub)halo, sometimes coupled with, or alternatively involving, the use of a sub halo finder and gas properties restrictions. Using the suite of high-res zoom re-sims of individual haloes, and the large-scale simulation MassiveBlack-II, examine the differences in measured galaxy properties from techniques with various aperture definitions. Perform techniques popular in the literature and present a new technique, based on the baryonic mass profiles of simulated (sub) haloes. For the average MW-mass system, find the two most popular techniques in the literature return differences of order 30% for stellar mass, a factor of 3 for gas mass, 40% for SFR, and factors of several for gas accretion and ejection rates. Individual cases can show variations greater than this, with the severity dependent on the concentration of a given system. The average difference in integrated properties for a more general galaxy population are not as striking, but are still significant for stellar and gas mass. The large differences that can occur are problematic for comparing results from various publications. Stress the importance of both defining and justifying a technique choice and discourage using popular apertures that use an exact fraction of the virial radius, due to the unignorable variation in galaxy-to-(sub)halo size. Finally, note that technique choice does not greatly affect simulated galaxies from lying within the scatter of observed scaling relations, but it can alter the derived best-fit slope for the Kennicutt-Schmidt relation.
1404.4069
Bending and breathing modes of the galactic disk
Widrow et al
Explore the hypothesis that a passing satellite or DM sub halo has excited coherent oscillations of the MW's stellar disk in the direction perpendicular to the Galactic mid plane. This work is motivated by recent observations of spatially dependent bulk vertical motions within ~kpc of the Sun. A satellite can transfer a fraction of its orbital energy to the disk stars as it plunges through the Galactic mid plane thereby heating and thickening the disk. Bulk motions arise during the early stages of such an even when the disk is still in an unrelaxed state. Present simple toy-model calculations and simulations of disk-satellite interactions, which show that the response of the disk depends on the relative velocity of the satellite. When the component of the satellite's velocity perpendicular to the disk is small compared with that of the stars, the perturbation is predominantly a bending mode. Conversely, breathing and higher order modes are excited when the vertical velocity of the satellite is larger than that of the stars. Argue that the compression and rarefaction motions in three different surveys are in fact breathing mode perturbations of the Galactic disk.
1404.4049
A census of the expected properties of classical Milky Way dwarfs in Milgomian dynamics
Lüghausen, Famaey, Kroupa
Revisit the classical MW dwarf spherical satellites Draco, Sculptor, Sextans, Carina, and Fornax in the framework of MOND, following the successful predictions of Andromeda's satellite galaxies. Use a Poisson solver with adaptive mesh refinement in order to account simultaneously for the gravitational influence of the MW and its satellites. This allows to rigorously model the important external field effect (EFE) of MOND, which can reduce the effective acceleration significantly. Make predictions on the M_dyn/L expected to be measured by an observer who assumes Newtonian dynamics to be valid. Show that MIlgromian dynamics predicts typical M_dyn/L~10…50 Msun/Lsun. The results for the most luminous ons, Fornax and Sculptor, agree well with available velocity dispersion data. The central power law slopes of the dynamical masses agrees exceedingly well with values inferred observationally from velocity dispersion measurements. The results for Sextans, Carina and Draco are low compared to usually quoted observational estimates, as already pointed out by Angus (2008). For MOND to survive further observational tests in these objects, one would need that either a) previous observational findings based on velocity dispersion measurements have overestimated the dynamical mass due to e.g., binaries and contaminant outliers, b) the satellites are not in virial equilibrium due to the MW tidal field, or c) the specific theory used here does not describe the EFE correctly (e.g., the EFE could be practically negligible in some other theories), or a combination of the three.
1404.4053
Where do galaxies end? a study of hydrodynamic-simulation galaxies and their integrated properties
Stevens, Martig, Croton, Feng
In Hydrosims, often a spherical aperture defines the boundary between the galaxy and the rest of its parent (sub)halo, sometimes coupled with, or alternatively involving, the use of a sub halo finder and gas properties restrictions. Using the suite of high-res zoom re-sims of individual haloes, and the large-scale simulation MassiveBlack-II, examine the differences in measured galaxy properties from techniques with various aperture definitions. Perform techniques popular in the literature and present a new technique, based on the baryonic mass profiles of simulated (sub) haloes. For the average MW-mass system, find the two most popular techniques in the literature return differences of order 30% for stellar mass, a factor of 3 for gas mass, 40% for SFR, and factors of several for gas accretion and ejection rates. Individual cases can show variations greater than this, with the severity dependent on the concentration of a given system. The average difference in integrated properties for a more general galaxy population are not as striking, but are still significant for stellar and gas mass. The large differences that can occur are problematic for comparing results from various publications. Stress the importance of both defining and justifying a technique choice and discourage using popular apertures that use an exact fraction of the virial radius, due to the unignorable variation in galaxy-to-(sub)halo size. Finally, note that technique choice does not greatly affect simulated galaxies from lying within the scatter of observed scaling relations, but it can alter the derived best-fit slope for the Kennicutt-Schmidt relation.
1404.4069
Bending and breathing modes of the galactic disk
Widrow et al
Explore the hypothesis that a passing satellite or DM sub halo has excited coherent oscillations of the MW's stellar disk in the direction perpendicular to the Galactic mid plane. This work is motivated by recent observations of spatially dependent bulk vertical motions within ~kpc of the Sun. A satellite can transfer a fraction of its orbital energy to the disk stars as it plunges through the Galactic mid plane thereby heating and thickening the disk. Bulk motions arise during the early stages of such an even when the disk is still in an unrelaxed state. Present simple toy-model calculations and simulations of disk-satellite interactions, which show that the response of the disk depends on the relative velocity of the satellite. When the component of the satellite's velocity perpendicular to the disk is small compared with that of the stars, the perturbation is predominantly a bending mode. Conversely, breathing and higher order modes are excited when the vertical velocity of the satellite is larger than that of the stars. Argue that the compression and rarefaction motions in three different surveys are in fact breathing mode perturbations of the Galactic disk.
Tuesday, April 15, 2014
Day 629
Wednesday.
1404.3724
Bent by baryons: the low mass galaxy-halo relation
Sawala, Frenk, … Navarro, Bower, et al
The relation between galaxies and DM haloes is important for evaluating theoretical predictions of structure formation and galaxy formation physics. Show that the widely used method of abundance matching based on DM only simulations fails at the low mass end because two of its underlying assumptions are broken: only a small fraction of low mass (below 1e9.5 Msun) haloes host a visible galaxy, and haloes grow at a lower rate due to the effect of baryons. In this regime, reliance on DM only simulations for abundance matching is neither accurate nor self-consistent. Find that the reported discrepancy between observational estimates of the halo masses of dwarf galaxies and the values predicted by abundance matching does not point to a failure of LCDM, but simply to a failure to account for baryonic effects. Results also imply that the Local Group contains only a few hundred observable galaxies in contrast with the thousands of faint dwarfs that abundance matching would suggest. Show how relations derived from abundance matching can be corrected, so that they can be used self-consistently to calibrate models of galaxy formation.
1404.3725
Constraining primordial non-gaussianity with moments of the large scale density field
Mao, … Scoccimarro, et al
Use N-body sims to investigate whether measurements of large-scale structure can yield constraints on primordial non-Gaussianity. Measure the variance, skewness, and kurtosis of the evolved density field from simulations with Gaussian and 3 different non-Gaussian ICs: a local model with f_NL=100, an equilateral model with f_NL=-400, and an orthogonal model with f_NL=-400. Show that the moments of the DM density field differ significantly between Gaussian and non-Gaussian models. Also make the measurements on mock galaxy catalogs that contain galaxies with clustering properties similar to those of LRGs. Find that, in the case of skewness and kurtosis, galaxy bias reduces the detectability of non-Gaussianity, though still able to clearly discriminate between different models in the simulation volume. In the case of the variance, galaxy bias greatly amplifies the detectability of non-Gaussianity. In all cases, find that z distortions do not significantly affect the detectability. When restricted to measurements of volumes equivalent to SDSS-II or BOSS samples, the probability of detecting a departure from the Gaussian model is high by using measurements of the variance, but very low by using only skewness and kurtosis measurements. Find that skewness and kurtosis measurements are never likely to yield useful constraints on primordial non-Gaussianity, but future surveys should be large enough to place meaningful constraints using measurements of the galaxy variance.
1404.3730
Tensor-induced B modes with no temperature fluctuations
Kamionkowski, Dai, Jeong
The recent indications for r~=0.2 from BICEP2 measurements of CMB B-mode polarization present some tension with upper limits r<~0.1 from CMB temperature fluctuations. Point out that tensor perturbations can induce B modes in the CMB polarization without inducing any temperature fluctuations nor E-mode polarization whatsoever, but only, at the expense of violating the Copernican principle. Present this mathematical possibility as a new ingredient for the model-builder's toolkit in case the tension between B modes and temperature fluctuations cannot be resolved with more conventional ideas.
1404.3742
A 2.5% measurement of the growth rate from small-scale redshift space clustering of SDSS-III CMASS galaxies
Reid, Seo, Leauthaud, Tinker, White
Perform the fit to the anisotropic clustering of SDSS-III CMASS DR10 galaxies on scales of ~0.8 - 32 Mpc/h. A standard halo occupation distribution model evaluated near the best fit Planck LCDM cosmology provides a good fit to the observed anisotropic clustering, and implies a normalization for the peculiar velocity field of M~2e13 Msun/h haloes of f*sigma8(z=0.57)=0.450 pm 0.011. Since this constraint includes both quasi-linear and NL scales, it should severely constrain modified gravity models that enhance pairwise infall velocities on these scales. Though model dependent, measurement represents a factor of 2.5 improvement in precision over the analysis of DR11 on large scales, f*sigma8(z=0.57)=0.446pm0.028, and is the tightest single constraint on the growth rate of cosmic structure to date. Measurement is consistent with the Planck LCDM prediction of 0.48pm0.010 at the ~1.9 sigma level. Assuming a halo mass function evaluated at the best fit Planck cosmology, also find that 10% of CMASS galaxies are satellites in haloes of mass M~6e13 Msun/h. While none of the tests and model generalization indicate systematic errors due to an insufficiently detailed model of the galaxy-halo connection, the precision of these first results warrant further investigation into the modeling uncertainties and degeneracies with cosmological parameters.
1404.3799
The 6dF galaxy velocity survey: cosmological constraints from the velocity power spectrum
Johnson, Blake, et al
The scale-dependent measurements of the normalized growth rate of structure f*sigma_8(k,z=0) using only the peculiar motions of galaxies. Use data from the 6dFGSv together with a newly-compiled sample of z<0.07 type Ia SNe. Constrain the growth rate in a series of Delta k ~ 0.03 h/Mpc bins to ~35 precision, including a measurement on scales >300Mpc/h, which represents the largest-scale growth rate measurement to date. Find no evidence for a scale dependence in the growth rate, or any statistically significant variation from the growth rate as predicted by the Planck cosmology. Bringing all the scales together, determine the normalized growth rate at z=0 to ~15 in a matter independent of galaxy bias and in excellent agreement with the constraint from the measurements of z-space distortions from 6dFGS. Pay attention to systematic errors. Point out that the intrinsic scatter present in Fundamental-Plane and Tully-Fisher relations is only Gaussian in logarithmic distance units; wrongly assuming it is Gaussian in linear (velocity) units can bias cosmological constraints. Also analytically marginalize over zero-point errors in distance indicators, validate the accuracy of all the constraints using numerical simulations, and demonstrate how to combine different (correlated) velocity surveys using a matrix 'hyper-parmeter' analysis. Current and forthcoming peculiar velocity surveys will allow to understand in detail the growth of structure in the low-z universe, providing strong constraints on the nature of DE.
1404.3724
Bent by baryons: the low mass galaxy-halo relation
Sawala, Frenk, … Navarro, Bower, et al
The relation between galaxies and DM haloes is important for evaluating theoretical predictions of structure formation and galaxy formation physics. Show that the widely used method of abundance matching based on DM only simulations fails at the low mass end because two of its underlying assumptions are broken: only a small fraction of low mass (below 1e9.5 Msun) haloes host a visible galaxy, and haloes grow at a lower rate due to the effect of baryons. In this regime, reliance on DM only simulations for abundance matching is neither accurate nor self-consistent. Find that the reported discrepancy between observational estimates of the halo masses of dwarf galaxies and the values predicted by abundance matching does not point to a failure of LCDM, but simply to a failure to account for baryonic effects. Results also imply that the Local Group contains only a few hundred observable galaxies in contrast with the thousands of faint dwarfs that abundance matching would suggest. Show how relations derived from abundance matching can be corrected, so that they can be used self-consistently to calibrate models of galaxy formation.
1404.3725
Constraining primordial non-gaussianity with moments of the large scale density field
Mao, … Scoccimarro, et al
Use N-body sims to investigate whether measurements of large-scale structure can yield constraints on primordial non-Gaussianity. Measure the variance, skewness, and kurtosis of the evolved density field from simulations with Gaussian and 3 different non-Gaussian ICs: a local model with f_NL=100, an equilateral model with f_NL=-400, and an orthogonal model with f_NL=-400. Show that the moments of the DM density field differ significantly between Gaussian and non-Gaussian models. Also make the measurements on mock galaxy catalogs that contain galaxies with clustering properties similar to those of LRGs. Find that, in the case of skewness and kurtosis, galaxy bias reduces the detectability of non-Gaussianity, though still able to clearly discriminate between different models in the simulation volume. In the case of the variance, galaxy bias greatly amplifies the detectability of non-Gaussianity. In all cases, find that z distortions do not significantly affect the detectability. When restricted to measurements of volumes equivalent to SDSS-II or BOSS samples, the probability of detecting a departure from the Gaussian model is high by using measurements of the variance, but very low by using only skewness and kurtosis measurements. Find that skewness and kurtosis measurements are never likely to yield useful constraints on primordial non-Gaussianity, but future surveys should be large enough to place meaningful constraints using measurements of the galaxy variance.
1404.3730
Tensor-induced B modes with no temperature fluctuations
Kamionkowski, Dai, Jeong
The recent indications for r~=0.2 from BICEP2 measurements of CMB B-mode polarization present some tension with upper limits r<~0.1 from CMB temperature fluctuations. Point out that tensor perturbations can induce B modes in the CMB polarization without inducing any temperature fluctuations nor E-mode polarization whatsoever, but only, at the expense of violating the Copernican principle. Present this mathematical possibility as a new ingredient for the model-builder's toolkit in case the tension between B modes and temperature fluctuations cannot be resolved with more conventional ideas.
1404.3742
A 2.5% measurement of the growth rate from small-scale redshift space clustering of SDSS-III CMASS galaxies
Reid, Seo, Leauthaud, Tinker, White
Perform the fit to the anisotropic clustering of SDSS-III CMASS DR10 galaxies on scales of ~0.8 - 32 Mpc/h. A standard halo occupation distribution model evaluated near the best fit Planck LCDM cosmology provides a good fit to the observed anisotropic clustering, and implies a normalization for the peculiar velocity field of M~2e13 Msun/h haloes of f*sigma8(z=0.57)=0.450 pm 0.011. Since this constraint includes both quasi-linear and NL scales, it should severely constrain modified gravity models that enhance pairwise infall velocities on these scales. Though model dependent, measurement represents a factor of 2.5 improvement in precision over the analysis of DR11 on large scales, f*sigma8(z=0.57)=0.446pm0.028, and is the tightest single constraint on the growth rate of cosmic structure to date. Measurement is consistent with the Planck LCDM prediction of 0.48pm0.010 at the ~1.9 sigma level. Assuming a halo mass function evaluated at the best fit Planck cosmology, also find that 10% of CMASS galaxies are satellites in haloes of mass M~6e13 Msun/h. While none of the tests and model generalization indicate systematic errors due to an insufficiently detailed model of the galaxy-halo connection, the precision of these first results warrant further investigation into the modeling uncertainties and degeneracies with cosmological parameters.
1404.3799
The 6dF galaxy velocity survey: cosmological constraints from the velocity power spectrum
Johnson, Blake, et al
The scale-dependent measurements of the normalized growth rate of structure f*sigma_8(k,z=0) using only the peculiar motions of galaxies. Use data from the 6dFGSv together with a newly-compiled sample of z<0.07 type Ia SNe. Constrain the growth rate in a series of Delta k ~ 0.03 h/Mpc bins to ~35 precision, including a measurement on scales >300Mpc/h, which represents the largest-scale growth rate measurement to date. Find no evidence for a scale dependence in the growth rate, or any statistically significant variation from the growth rate as predicted by the Planck cosmology. Bringing all the scales together, determine the normalized growth rate at z=0 to ~15 in a matter independent of galaxy bias and in excellent agreement with the constraint from the measurements of z-space distortions from 6dFGS. Pay attention to systematic errors. Point out that the intrinsic scatter present in Fundamental-Plane and Tully-Fisher relations is only Gaussian in logarithmic distance units; wrongly assuming it is Gaussian in linear (velocity) units can bias cosmological constraints. Also analytically marginalize over zero-point errors in distance indicators, validate the accuracy of all the constraints using numerical simulations, and demonstrate how to combine different (correlated) velocity surveys using a matrix 'hyper-parmeter' analysis. Current and forthcoming peculiar velocity surveys will allow to understand in detail the growth of structure in the low-z universe, providing strong constraints on the nature of DE.
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