Friday.
1410.8141
Forty-seven Milky Way-sized, extremely diffuse galaxies in the Coma Cluster
van Dokkum, ... Geha, Conroy, et al
Discovery of 47 low surface brightness objects in deep images of 3x3 deg field centered on the Coma cluster, obtained with the Dragonfly Telephoto Array. The objects have central surface brightness mu(g,0) ranging from 24-26 mag/arcsec2 and effective radii r_e=3-10", as measured from CFHT images. From their spatial distribution, infer that most or all of the objects are galaxies in the Coma cluster. This relatively large distance is surprising as it implies that the galaxies are very large: with r_e=1.5-4.6 kpc their sizes are similar to those of L* galaxies even though their median stellar mass is only ~6e7 Msun. The galaxies are relatively red and round, with <g-i> =0.8 and <b/a>=0.74. One of the 47 galaxies is fortuitously covered by a HST ACS observation. The ACS imaging shows a large spheroidal object with a central surface brightness mu(g,0)=25.8 mag/as2, a Sersic index n=0.6, and an effective radius of 7", corresponding to a 3.4 kpc at the distance of Coma. The galaxy is unresolved, as expected for a Coma cluster object. As known, such "ultra-diffuse galaxies" have not been predicted in any modern galaxy formation model. Speculate that UDGs may have lost their gas supply at early times, possibly resulting in very high DM fractions.
1410.8161
Star formation quenching in simulated group and cluster galaxies: when, how, and why?
Bahe, McCarthy
SF is observed to be suppressed in group and cluster galaxies compared to the field. Analyze ~2k galaxies in cosmo hydro sims. Time of quenching varies from ~2Gyr before accretion (first crossing of r200,c) to >4 Gyr after, depending on satellite and host mass. Once begun, quenching is rapid (>~500 Myr) in low-mass galaxies (M*<1e10 Msun), but significantly more protracted for more massive satellites. The simulation predict a substantial role of outflows driven by ram pressure - but not tidal forces - in removing the SF ISM from satellite galaxies, especially dwarfs (M*~1e9 Msun) where they account for nearly 2/3 of ISM loss in both groups and clusters. Immediately before quenching is complete, this fraction rises to ~80% even for MW analogues (M*~1e10.5 Msun) in groups (M_host~1d13.5 Msun). Show that (i) ISM stripping was significantly more effective at early times than at z=0; (ii) approximately half the gas is stripped from `galactic fountains` and half directly from the SF disk; (iii) galaxies undergoing stripping experience ram pressure up to ~100 times the average at a given group/cluster-centric raids, because they are preferentially located in overdense ICM regions. Remarkably, stripping causes at most half the loss of the extended gas haloes surrounding the simulated satellites. These results contrast sharply with the current picture of strangulation - removal of the ISM through SF after stripping of the hot halo - being the dominant mechanism quenching group and cluster satellites.
1410.8452
Born-corrections to weak lensing of the cosmic microwave background temperature and polarisation anisotropies
Hagstotz, Schäfer, Merkel
Affects especially the polarization spectra, leading to relative changes of the order of 1% of the E-mode spectrum and up to 10% on all scales to the B-mode spectrum. In contrast, there is only little change of spectra involving the CMB temperature. The corrections excite one more degree of freedom resulting in a deflection component which can not be described as a gradient of the lensing potential as it is related to image rotation in lens-lens coupling. Estimate the magnitude of this effect on the CMB-spectra and find it to be negligible.
Thursday, October 30, 2014
Day 775
Thursday.
1410.7768
Effect of primordial non-Gaussianities on the far-UV luminosity function of high-redshift galaxies: implications for cosmic reionization
Chevallard, Silk, Nishimichi, Habouzit, Mamon, Peirani
IGM reionization at z>6 depend on FUV LF. Run 5 N-body sims with Gaussian and scale-dependent non-Gaussian IC, all consistent with Planck constraints. Compute the FUV galaxy luminosity function down to M_UV=-14 at 7<z<15. Find that models with strong primordial non-Gausisnities on <Mpc scales show a FUV LF significantly enhanced in low-mass galaxies. Adopt a reionization model calibrated from state-of-the-art hydrodynamical simulations and show that such non-Gaussianities leave a clear imprint on the Universe reionization history and electron Thomson scattering optical depth tau_E. Although current uncertainties in the physics of reionization and on the determination of tau_E still dominate the signatures of non-Gauassianities, results suggest that tau_E could ultimately be used to constrain the statistical properties of initial density fluctuations.
1410.7770
Measuring angular diameter distances of strong gravitational lenses
Jee, Komatsu, Suyu
Show that measurements of positions and time delays of strongly lensed images of a background galaxy, as well as those of the velocity dispersion and mass profile of a lens galaxy, can be combined to extract the angular diameter distance of the lens galaxy. Physically, as the velocity dispersion and the time delay give a gravitational potential (GM/r) and a mass (GM) of the lens, respectively, dividing them gives a physical size (r) of the lens. Comparing the physical size with the image positions of a lensed galaxy gives the angular diameter distance to the lens. A mismatch between the exact locations at which these measurements are made can be corrected by measuring a local slope of the mass profile. Expand on the original idea put forward by Paraficz and Hjorth, who analyzed singular isothermal lenses, by allowing for an arbitrary slope of a power-law spherical mass density profile, and external convergence, and an anisotropic velocity dispersion. Find that the effect of external convergence cancels out when dividing the time delays and velocity dispersion measurements. Derive a formula for the uncertainty in the angular diameter distance in terms of the uncertainties in the observables. As an application, use two existing SL systems to show that the uncertainty in the inferred angular diameter distances is dominated by that in the velocity dispersion, sigma^2, and its anisotropy. Find that the current data on these systems should yield about 16% uncertainty in DA per object. This improves to 13% when sigma^2 is measured at the so-called sweet-sopt radius. Achieving 7% is possible if sigma^2 is determined with 5% precision.
1410.7778
A new spin on disks of satellite galaxies
Cautun, Wang, Frenk, Sawala
The excess of satellites on opposite sides of their primaries having anti correlated radial velocities, found by Ibata+ in SDSS, is sensitive to small changes in the sample selection criteria, which can significantly reduce its significance. In addition, find no evidence for correspondingly correlated velocities for satellites observed on the same side of their primaries, which would be expected for rotating disks of satellites. Conclude that the detection of coherent rotation in satellite population in current observational samples is not robust. Compare data to the LCDM Millennium sims populated with galaxies according to the SAM of Guo+. Find excellent agreement with the spatial distribution of satellites in the SDSS data and the lack of strong signal from coherent rotation.
1410.7839
Weak lensing with sizes, magnitudes and shapes
Alsing, Kirk, Heavens, Jaffe
Galaxy shapes probe the shear field whilst size, magnitude and number density probe the convergence field. Both contain cosmo information. Use magnification of size and magnitude of individual galaxies as probe of cosmic convergence. Develop a Bayesian approach for inferring the convergence field from a measured size, magnitude and redshift and demonstrate that the inference on convergence requires detailed knowledge of the joint distribution of intrinsic sizes and magnitudes. Build a simple parameterized model for the size-magnitude distribution and estimate this distribution for CFHTLenS galaxies. In light of the measured distribution, show that the typical dispersion on convergence estimation is ~0.8, compared to ~0.38 for shear. Discuss the possibility of physical systematics for magnification (similar to IA for shear) and compute the expected gains in DE FoM from combining magnification with shear for different scenarios regarding systematics: when accounting for IA but no systematics on the magnification signal, including magnification could improve the FoM by unto a factor of ~2.5, whilst when accounting for physical systematics in both shear and magnification anticipate a gain between ~25% and 65%. In addition to the statistical gains, the fact that cosmic shear and magnification are subject to different systematics makes magnification an attractive complement to ay cosmic shear analysis.
1410.7946
Three Einstein rings: explicit solution and numerical simulation
Bannikova, Kotvytskiy
As the title says.
1410.7768
Effect of primordial non-Gaussianities on the far-UV luminosity function of high-redshift galaxies: implications for cosmic reionization
Chevallard, Silk, Nishimichi, Habouzit, Mamon, Peirani
IGM reionization at z>6 depend on FUV LF. Run 5 N-body sims with Gaussian and scale-dependent non-Gaussian IC, all consistent with Planck constraints. Compute the FUV galaxy luminosity function down to M_UV=-14 at 7<z<15. Find that models with strong primordial non-Gausisnities on <Mpc scales show a FUV LF significantly enhanced in low-mass galaxies. Adopt a reionization model calibrated from state-of-the-art hydrodynamical simulations and show that such non-Gaussianities leave a clear imprint on the Universe reionization history and electron Thomson scattering optical depth tau_E. Although current uncertainties in the physics of reionization and on the determination of tau_E still dominate the signatures of non-Gauassianities, results suggest that tau_E could ultimately be used to constrain the statistical properties of initial density fluctuations.
1410.7770
Measuring angular diameter distances of strong gravitational lenses
Jee, Komatsu, Suyu
Show that measurements of positions and time delays of strongly lensed images of a background galaxy, as well as those of the velocity dispersion and mass profile of a lens galaxy, can be combined to extract the angular diameter distance of the lens galaxy. Physically, as the velocity dispersion and the time delay give a gravitational potential (GM/r) and a mass (GM) of the lens, respectively, dividing them gives a physical size (r) of the lens. Comparing the physical size with the image positions of a lensed galaxy gives the angular diameter distance to the lens. A mismatch between the exact locations at which these measurements are made can be corrected by measuring a local slope of the mass profile. Expand on the original idea put forward by Paraficz and Hjorth, who analyzed singular isothermal lenses, by allowing for an arbitrary slope of a power-law spherical mass density profile, and external convergence, and an anisotropic velocity dispersion. Find that the effect of external convergence cancels out when dividing the time delays and velocity dispersion measurements. Derive a formula for the uncertainty in the angular diameter distance in terms of the uncertainties in the observables. As an application, use two existing SL systems to show that the uncertainty in the inferred angular diameter distances is dominated by that in the velocity dispersion, sigma^2, and its anisotropy. Find that the current data on these systems should yield about 16% uncertainty in DA per object. This improves to 13% when sigma^2 is measured at the so-called sweet-sopt radius. Achieving 7% is possible if sigma^2 is determined with 5% precision.
1410.7778
A new spin on disks of satellite galaxies
Cautun, Wang, Frenk, Sawala
The excess of satellites on opposite sides of their primaries having anti correlated radial velocities, found by Ibata+ in SDSS, is sensitive to small changes in the sample selection criteria, which can significantly reduce its significance. In addition, find no evidence for correspondingly correlated velocities for satellites observed on the same side of their primaries, which would be expected for rotating disks of satellites. Conclude that the detection of coherent rotation in satellite population in current observational samples is not robust. Compare data to the LCDM Millennium sims populated with galaxies according to the SAM of Guo+. Find excellent agreement with the spatial distribution of satellites in the SDSS data and the lack of strong signal from coherent rotation.
1410.7839
Weak lensing with sizes, magnitudes and shapes
Alsing, Kirk, Heavens, Jaffe
Galaxy shapes probe the shear field whilst size, magnitude and number density probe the convergence field. Both contain cosmo information. Use magnification of size and magnitude of individual galaxies as probe of cosmic convergence. Develop a Bayesian approach for inferring the convergence field from a measured size, magnitude and redshift and demonstrate that the inference on convergence requires detailed knowledge of the joint distribution of intrinsic sizes and magnitudes. Build a simple parameterized model for the size-magnitude distribution and estimate this distribution for CFHTLenS galaxies. In light of the measured distribution, show that the typical dispersion on convergence estimation is ~0.8, compared to ~0.38 for shear. Discuss the possibility of physical systematics for magnification (similar to IA for shear) and compute the expected gains in DE FoM from combining magnification with shear for different scenarios regarding systematics: when accounting for IA but no systematics on the magnification signal, including magnification could improve the FoM by unto a factor of ~2.5, whilst when accounting for physical systematics in both shear and magnification anticipate a gain between ~25% and 65%. In addition to the statistical gains, the fact that cosmic shear and magnification are subject to different systematics makes magnification an attractive complement to ay cosmic shear analysis.
1410.7946
Three Einstein rings: explicit solution and numerical simulation
Bannikova, Kotvytskiy
As the title says.
Tuesday, October 28, 2014
Day 774
Wednesday.
1410.7391
The metallicity of galactic winds
Creasey, Theuns, Bower
Find that winds from more massive galaxies are hotter and more highly enriched, in stark contrast to that which is often assumed in galaxy formation models. Use these findings in a simple model of galactic enrichment evolution, in which the metallicity of forming galaxies is the result of accretion of nearly pristine gas and outflow of enriched gas along an equilibrium sequence. Compare these predictions to the observed mass-metallicity relation, and demonstrate how the galaxy's gas fraction is a key controlling parameter. This explains the observed flattening of the mass-metallicity relation at higher stellar masses.
1410.7400
The colors of satellite galaxies in the Illustris Simulation
Sales, Vogelsberger, Genel, ... Springel, Hernquist
Observationally, the fraction of blue satellite galaxies decreases steeply with host halo mass, and their radial distribution around central galaxies is significantly shallower in massive (M*>1e11 Msun) than in MW-like systems. Theoretical models, based primarily on SAM techniques, have had a long-standing problem with reproducing these trends, instead predicting too few blue satellites in general but also estimating a radial distribution that is too shallow, regardless of primary mass. In this Letter, use the Illustrious cosmological simulation to study the properties of satellite galaxies around isolated primaries. For the first time, find good agreement between theory and observations. Identify the main source of this success relative to earlier work to be a consequence of the large gas contents of satellite at infall, a factor ~5-10 times larger than in SAMs. Because of their relatively large gas reservoirs, satellites can continue to form stars long after infall, which a typical timescale for SF to be quenched ~2Gyr in groups but more than ~5Gyr for satellites around MW-like primaries. The gas contents inferred are consistent with z=0 observations of HI gas in galaxies, although find large discrepancies among reported values in the literature. A testable prediction of the model is that the gas-to-stellar mass ratio of satellite progenitors should vary only weakly with cosmic time.
1410.7515
Core shapes and orientations of core-Sersic galaxies
Dullo, Graham
24 core-Sersic galaxies using HST images. Select galaxies with ellipticity and position angle measurements that are robust against HST seeing. For bulk of the galaxies, there is a good agreement between the ellipticities and position angles at the break radii and the average outer ellipticities and position angles determined over R_e < 2 < R_e, where R_e is the spheroids' effective HLR. However there are some interesting differences. Find a median "inner" ellipticity at R_b of e_med=0.13pm0.01, rounder than the median ellipticity of the "outer" regions e_med=0.20pm0.01, which is thought to reflect the influence of the central SMBH at small radii. In addition find a trend albeit weak (2 sigma), such that galaxies with larger (stellar deficit)-to-(SMBH) mass ratios - thought to be a measure of the number of major dry merger events - tend to have rounder inner and outer isophotes, suggesting a connection between the galaxy shapes and their mergers histories. Show that this finding is not simply reflecting the well known result that more luminous galaxies are rounder, but it is no doubt related.
1410.7391
The metallicity of galactic winds
Creasey, Theuns, Bower
Find that winds from more massive galaxies are hotter and more highly enriched, in stark contrast to that which is often assumed in galaxy formation models. Use these findings in a simple model of galactic enrichment evolution, in which the metallicity of forming galaxies is the result of accretion of nearly pristine gas and outflow of enriched gas along an equilibrium sequence. Compare these predictions to the observed mass-metallicity relation, and demonstrate how the galaxy's gas fraction is a key controlling parameter. This explains the observed flattening of the mass-metallicity relation at higher stellar masses.
1410.7400
The colors of satellite galaxies in the Illustris Simulation
Sales, Vogelsberger, Genel, ... Springel, Hernquist
Observationally, the fraction of blue satellite galaxies decreases steeply with host halo mass, and their radial distribution around central galaxies is significantly shallower in massive (M*>1e11 Msun) than in MW-like systems. Theoretical models, based primarily on SAM techniques, have had a long-standing problem with reproducing these trends, instead predicting too few blue satellites in general but also estimating a radial distribution that is too shallow, regardless of primary mass. In this Letter, use the Illustrious cosmological simulation to study the properties of satellite galaxies around isolated primaries. For the first time, find good agreement between theory and observations. Identify the main source of this success relative to earlier work to be a consequence of the large gas contents of satellite at infall, a factor ~5-10 times larger than in SAMs. Because of their relatively large gas reservoirs, satellites can continue to form stars long after infall, which a typical timescale for SF to be quenched ~2Gyr in groups but more than ~5Gyr for satellites around MW-like primaries. The gas contents inferred are consistent with z=0 observations of HI gas in galaxies, although find large discrepancies among reported values in the literature. A testable prediction of the model is that the gas-to-stellar mass ratio of satellite progenitors should vary only weakly with cosmic time.
1410.7515
Core shapes and orientations of core-Sersic galaxies
Dullo, Graham
24 core-Sersic galaxies using HST images. Select galaxies with ellipticity and position angle measurements that are robust against HST seeing. For bulk of the galaxies, there is a good agreement between the ellipticities and position angles at the break radii and the average outer ellipticities and position angles determined over R_e < 2 < R_e, where R_e is the spheroids' effective HLR. However there are some interesting differences. Find a median "inner" ellipticity at R_b of e_med=0.13pm0.01, rounder than the median ellipticity of the "outer" regions e_med=0.20pm0.01, which is thought to reflect the influence of the central SMBH at small radii. In addition find a trend albeit weak (2 sigma), such that galaxies with larger (stellar deficit)-to-(SMBH) mass ratios - thought to be a measure of the number of major dry merger events - tend to have rounder inner and outer isophotes, suggesting a connection between the galaxy shapes and their mergers histories. Show that this finding is not simply reflecting the well known result that more luminous galaxies are rounder, but it is no doubt related.
Monday, October 27, 2014
Day 773
Tuesday.
410.6818
At the Argo simulation: II. The early build-up of the Hubble sequence
Fiacconi, Feldmann, Mayer
22 high z>3 galaxies in Argo cosmo zoom-in sim of grog-sized halo in high resolution (1e4 Msun, 100 pc): Identify major mergers as the main trigger for the formation of bulges, and the steepening of the circular velocity curves. Minor mergers and non-axisymmetric perturbations (stellar bars) drive the bulge growth in some cases. The specific angular momenta of the simulated disc components fairly match the values inferred from nearby galaxies of similar M* once the expected redshift evolution of disc sizes is accounted for. Conclude that morphological transformations of high z galaxies of intermediate mass are likely triggered by processes similar to those at low z and result in an early build-up of the Hubble sequence.
1410.6826
Baryonic effects on weak-lensing two-point statistics and its cosmological implications
Mohammed, Martizzi, Teyssier, Amara
Develop an extension of the Halo model that describes analytically the corrections to the matter PS due to the physics of baryons. Extend these correction to the WL shear angular power spectrum. Within each halo, baryonic model accounts for : 1) a central galaxy, the major stellar component whose properties are derived from abundance matching techniques; 2) a hot plasma in hydrostatic equilibrium and 3) an adiabatically-contracted DM component. This analytic approach allows comparison of the model to the DM-only case. The basic assumptions are tested against the hydrodynamical simulations of Martizzi+ 2014, with which a remarkable agreement is found. The baryonic model has only one free parameter, M_crit, the critical halo mass that marks the transition between feedback-dominated haloes, mostly devoid of gas, and gas rich haloes, in which AGN feedback effects become weaker. Explore the entire cosmological parameter space, using the angular power spectrum in 3 z bins as the observable, assuming a Euclid-like survey. Derive the corresponding constraints on the cosmological parameters, as well as the possible bias introduced by neglecting the effects of baryonic physics. Find that, up to ell_max=4000, baryonic physics plays very little role in the cosmo parameter estimation. However, if one goes up to ell_max=8000, the marginalized errors on the cosmo parameters can be significantly reduced, but neglecting baryonic physics can lead to bias in the recovered cosmological parameters up to 10 sigma. These biases are removed if one takes into account the main baryonic parameter, M_crit, which can also be determined up to 1-2%, along with the other cosmological parameters.
1410.6955
A new model to predict weak lensing peak counts I. comparison with $N$-body simulations
Lin, Kilbinger
WL peak counts has been shown to be a powerful tool for cosmo. It provides non-Gaussian information of LSS, complementary to second order statistics. Propose a new flexible method to predict WL peak counts, which can be adapted to realistic scenarios, such as a real source distribution, intrinsic galaxy alignment, mass effects, photo-z errors from surveys, etc. The new model is also suitable for applying the tomography technique and NL filters. A probabilistic approach to model peak counts is pretend. First, sample halos from a MF. Second, assign them NFW profiles. Third, place haloes randomly on the field of view. The creation of these "fast sims" requires much less computing time compared to N-body runs. Then, perform ray-tracing through these fast simulation boxes and select peaks from WL maps to predict peak number counts. The computation is achieved by CAMELUS algorithm, which is made available at cosmostat.org. Compare results to N-body sims to validate the model. Find that the approach is in good agreement with full N-body runs. Show that the lensing signal dominates shape noise and Poisson noise for peaks with SNR between 4 and 6. Counts from the same SNR range are sensitive to Omega_m and sigma_8. Show how the model can discriminate between various combinations of these two parameters. Offer a powerful tool to study WL peaks. The potential of the forward model is its high flexibility, making the use of peak counts under realistic survey conditions feasible.
1410.7175
Dark matter inner slope and concentration in galaxies: from the Fornax dwarf to M87
Mamon et al
Apply 2 new methods that model the distribution of observed tracers in projected phase space to lift the mass/velocity anisotropy (VA) degeneracy and deduce constraints on the mass profiles of galaxies, as well as their VA. First show how a distribution function based method applied to the satellite kinematics of otherwise isolated SDSS galaxies shows convincing observational evidence of age matching: red galaxies have more concentrated DM haloes than blue galaxies of the same stellar or halo mass. Then, applying the MAMPOSSt technique to M87 (traced by its red and blue globular clusters) find that very cuspy DM is favored, unless priors are released on DM or stellar mass (leading to unconstrained slope). For the Fornax dSph (traced by its metal-rich and metal-poor stars), the inner DM slope is unconstrained, with weak evidence for a core if the stellar mass is fixed. This highlights how priors are crucial for DM modeling. Finally, find that blue GCs around M87 and metal-rich stars in Fornax have tangential outer VA.
410.6818
At the Argo simulation: II. The early build-up of the Hubble sequence
Fiacconi, Feldmann, Mayer
22 high z>3 galaxies in Argo cosmo zoom-in sim of grog-sized halo in high resolution (1e4 Msun, 100 pc): Identify major mergers as the main trigger for the formation of bulges, and the steepening of the circular velocity curves. Minor mergers and non-axisymmetric perturbations (stellar bars) drive the bulge growth in some cases. The specific angular momenta of the simulated disc components fairly match the values inferred from nearby galaxies of similar M* once the expected redshift evolution of disc sizes is accounted for. Conclude that morphological transformations of high z galaxies of intermediate mass are likely triggered by processes similar to those at low z and result in an early build-up of the Hubble sequence.
1410.6826
Baryonic effects on weak-lensing two-point statistics and its cosmological implications
Mohammed, Martizzi, Teyssier, Amara
Develop an extension of the Halo model that describes analytically the corrections to the matter PS due to the physics of baryons. Extend these correction to the WL shear angular power spectrum. Within each halo, baryonic model accounts for : 1) a central galaxy, the major stellar component whose properties are derived from abundance matching techniques; 2) a hot plasma in hydrostatic equilibrium and 3) an adiabatically-contracted DM component. This analytic approach allows comparison of the model to the DM-only case. The basic assumptions are tested against the hydrodynamical simulations of Martizzi+ 2014, with which a remarkable agreement is found. The baryonic model has only one free parameter, M_crit, the critical halo mass that marks the transition between feedback-dominated haloes, mostly devoid of gas, and gas rich haloes, in which AGN feedback effects become weaker. Explore the entire cosmological parameter space, using the angular power spectrum in 3 z bins as the observable, assuming a Euclid-like survey. Derive the corresponding constraints on the cosmological parameters, as well as the possible bias introduced by neglecting the effects of baryonic physics. Find that, up to ell_max=4000, baryonic physics plays very little role in the cosmo parameter estimation. However, if one goes up to ell_max=8000, the marginalized errors on the cosmo parameters can be significantly reduced, but neglecting baryonic physics can lead to bias in the recovered cosmological parameters up to 10 sigma. These biases are removed if one takes into account the main baryonic parameter, M_crit, which can also be determined up to 1-2%, along with the other cosmological parameters.
1410.6955
A new model to predict weak lensing peak counts I. comparison with $N$-body simulations
Lin, Kilbinger
WL peak counts has been shown to be a powerful tool for cosmo. It provides non-Gaussian information of LSS, complementary to second order statistics. Propose a new flexible method to predict WL peak counts, which can be adapted to realistic scenarios, such as a real source distribution, intrinsic galaxy alignment, mass effects, photo-z errors from surveys, etc. The new model is also suitable for applying the tomography technique and NL filters. A probabilistic approach to model peak counts is pretend. First, sample halos from a MF. Second, assign them NFW profiles. Third, place haloes randomly on the field of view. The creation of these "fast sims" requires much less computing time compared to N-body runs. Then, perform ray-tracing through these fast simulation boxes and select peaks from WL maps to predict peak number counts. The computation is achieved by CAMELUS algorithm, which is made available at cosmostat.org. Compare results to N-body sims to validate the model. Find that the approach is in good agreement with full N-body runs. Show that the lensing signal dominates shape noise and Poisson noise for peaks with SNR between 4 and 6. Counts from the same SNR range are sensitive to Omega_m and sigma_8. Show how the model can discriminate between various combinations of these two parameters. Offer a powerful tool to study WL peaks. The potential of the forward model is its high flexibility, making the use of peak counts under realistic survey conditions feasible.
1410.7175
Dark matter inner slope and concentration in galaxies: from the Fornax dwarf to M87
Mamon et al
Apply 2 new methods that model the distribution of observed tracers in projected phase space to lift the mass/velocity anisotropy (VA) degeneracy and deduce constraints on the mass profiles of galaxies, as well as their VA. First show how a distribution function based method applied to the satellite kinematics of otherwise isolated SDSS galaxies shows convincing observational evidence of age matching: red galaxies have more concentrated DM haloes than blue galaxies of the same stellar or halo mass. Then, applying the MAMPOSSt technique to M87 (traced by its red and blue globular clusters) find that very cuspy DM is favored, unless priors are released on DM or stellar mass (leading to unconstrained slope). For the Fornax dSph (traced by its metal-rich and metal-poor stars), the inner DM slope is unconstrained, with weak evidence for a core if the stellar mass is fixed. This highlights how priors are crucial for DM modeling. Finally, find that blue GCs around M87 and metal-rich stars in Fornax have tangential outer VA.
Sunday, October 26, 2014
Day 772
Monday.
1410.6481
From blue star-forming to red passive: galaxies in transition in different environments
Vulcani, et al
Exploit a mass complete (M*>1e10.25 Msun) sample at 0.03<z<0.11 from PM2GC, use (U_B)_rf color and morphologies to characterize galaxies, in particular those that show signs of an ongoing or recent transformation of their SF activity and/or morphology - green galaxies, red passive late types, and blue star-forming early types. Color fractions depend on mass and only for M*<1e10.7M_sun on environment. The incidence of red galaxies increases with increasing mass, and, for M*<1e10.7 Msun, decreases toward the group outskirts and in binary and single galaxies. The relative abundance of green and blue galaxies is independent of environment, and increases monotonically with galaxy mass. Also inspect galaxy structural parameters, SF properties, histories and ages and propose and evolutionary scenario for the different subpopulations. Color transformations are due to a reduction and suppression of SFR in both bulges and disks which does not noticeably affect galaxy structure. Morphological transitions are linked to an enhanced bulge-to-disk ratio due to the removal of the disk, not to an increase of the bulge. The model suggests that green colors might be due to SFHs declining with long timescales, as an alternative scenario to the classical "quenching" processes. Results suggest that galaxy transformations in SF activity and morphology depend neither on environment nor on being a satellite or the most massive galaxy of a halo. The only environmental dependence found is the higher fast quenching efficiency in groups giving origin to post-starburst signatures.
Rayleigh scattering: Primarily elastic scattering of light by particles much smaller than the wavelength of the light.
1410.6484
The effects of Rayleigh scattering on the CMB and cosmic structure
Alipour, Sigurdson, Hirata
During and after recombination, in addition to Thomson scattering with free electrons, photons also coupled to neutral hydrogen and helium atoms through Rayleigh scattering. This coupling influences both CMB anisotropies and the distribution of matter in the Universe. The frequency-dependence of the Rayleigh cross section breaks the thermal nature of CMB temperature and polarization anisotropy and effectively doubles the number of variables needed to describe CMB intensity and polarization statistics, while the additional atomic coupling changes the matter distribution and the lensing of the CMB. Introduce a new method to capture the effects of Rayleigh scattering on cosmological PS. Rayleigh scattering modifies CMB temperature and polarization anisotropies at the ~1% feel at 353 GHz (scaling ~ nu^4), and modifies matter correlations by as much as ~0.3%. Show the Rayleigh signal, especially the cross-spectra between the thermal (Rayleigh) E-polarization and Rayleigh (thermal) intensity signal, may be detectable with future CMB missions even in the presence of foregrounds, and how this new information might help to better constrain the cosmological parameters.
1410.6557
Radio monitoring campaigns of six strongly lensed quasars
Rumbaugh, Fassnacht, ... Koopmans, .... Suyu, et al
Observed 6 LS, radio-loud quasars. It was not possible to measure time delays from the data, but found evidence for variability in a majority of the light curves. Most of these systems should be targeted with followup monitoring campaigns.
1410.6597
The Void Galaxy Survey: galaxy evolution and gas accretion in voids
Kreckel et al
Select 59 galaxies in the deepest underdensities. Find deep UV, optical, Halvah, IR and HI imaging to study the morphology and kinematics of both the stellar and gaseous components. This sample allows not only examination of the global statistical properties of void galaxies, but also to explore the details of the dynamical properties. Present and overview of the VGS, and highlight key results on the HI content and individually interesting systems. In general, find that the void galaxies are gas rich, low luminosity, blue disk galaxies, with optical and HI properties that are not unusual for their luminosity and morphology. See evidence of both ongoing assembly, through the gas dynamics between interacting systems, and significant gas accretion, seen in extended gas disks and kinematic misalignments. The VGS establishes a local reference sample to be used in future HI surveys that will directly observe the HI evolution of void galaxies over cosmic time.
1410.6481
From blue star-forming to red passive: galaxies in transition in different environments
Vulcani, et al
Exploit a mass complete (M*>1e10.25 Msun) sample at 0.03<z<0.11 from PM2GC, use (U_B)_rf color and morphologies to characterize galaxies, in particular those that show signs of an ongoing or recent transformation of their SF activity and/or morphology - green galaxies, red passive late types, and blue star-forming early types. Color fractions depend on mass and only for M*<1e10.7M_sun on environment. The incidence of red galaxies increases with increasing mass, and, for M*<1e10.7 Msun, decreases toward the group outskirts and in binary and single galaxies. The relative abundance of green and blue galaxies is independent of environment, and increases monotonically with galaxy mass. Also inspect galaxy structural parameters, SF properties, histories and ages and propose and evolutionary scenario for the different subpopulations. Color transformations are due to a reduction and suppression of SFR in both bulges and disks which does not noticeably affect galaxy structure. Morphological transitions are linked to an enhanced bulge-to-disk ratio due to the removal of the disk, not to an increase of the bulge. The model suggests that green colors might be due to SFHs declining with long timescales, as an alternative scenario to the classical "quenching" processes. Results suggest that galaxy transformations in SF activity and morphology depend neither on environment nor on being a satellite or the most massive galaxy of a halo. The only environmental dependence found is the higher fast quenching efficiency in groups giving origin to post-starburst signatures.
Rayleigh scattering: Primarily elastic scattering of light by particles much smaller than the wavelength of the light.
1410.6484
The effects of Rayleigh scattering on the CMB and cosmic structure
Alipour, Sigurdson, Hirata
During and after recombination, in addition to Thomson scattering with free electrons, photons also coupled to neutral hydrogen and helium atoms through Rayleigh scattering. This coupling influences both CMB anisotropies and the distribution of matter in the Universe. The frequency-dependence of the Rayleigh cross section breaks the thermal nature of CMB temperature and polarization anisotropy and effectively doubles the number of variables needed to describe CMB intensity and polarization statistics, while the additional atomic coupling changes the matter distribution and the lensing of the CMB. Introduce a new method to capture the effects of Rayleigh scattering on cosmological PS. Rayleigh scattering modifies CMB temperature and polarization anisotropies at the ~1% feel at 353 GHz (scaling ~ nu^4), and modifies matter correlations by as much as ~0.3%. Show the Rayleigh signal, especially the cross-spectra between the thermal (Rayleigh) E-polarization and Rayleigh (thermal) intensity signal, may be detectable with future CMB missions even in the presence of foregrounds, and how this new information might help to better constrain the cosmological parameters.
1410.6557
Radio monitoring campaigns of six strongly lensed quasars
Rumbaugh, Fassnacht, ... Koopmans, .... Suyu, et al
Observed 6 LS, radio-loud quasars. It was not possible to measure time delays from the data, but found evidence for variability in a majority of the light curves. Most of these systems should be targeted with followup monitoring campaigns.
1410.6597
The Void Galaxy Survey: galaxy evolution and gas accretion in voids
Kreckel et al
Select 59 galaxies in the deepest underdensities. Find deep UV, optical, Halvah, IR and HI imaging to study the morphology and kinematics of both the stellar and gaseous components. This sample allows not only examination of the global statistical properties of void galaxies, but also to explore the details of the dynamical properties. Present and overview of the VGS, and highlight key results on the HI content and individually interesting systems. In general, find that the void galaxies are gas rich, low luminosity, blue disk galaxies, with optical and HI properties that are not unusual for their luminosity and morphology. See evidence of both ongoing assembly, through the gas dynamics between interacting systems, and significant gas accretion, seen in extended gas disks and kinematic misalignments. The VGS establishes a local reference sample to be used in future HI surveys that will directly observe the HI evolution of void galaxies over cosmic time.
Day 771
Sunday.
1410.6161
Galactic tides and the shape and orientation of dwarf galaxy satellites
Barber, Starkenburg, Navarro, McConnachie
Use cosmo N-body sims from Aquarius to study the tidal effects of a dark matter halo on the shape and orientation of its substructure. Although tides are often assumed to enhance sphericity and to stretch sub haloes tangentially, these effects are short lived: as in earlier work, find that sub haloes affected by tides become substantially more spherical and show a strong radial alignment toward the center of the host halo. These results, combined with SAM of galaxy formation, may be used to assess the effect of Galactic tides on the observed population of dSph satellites of the MW and Andromeda galaxies. If the relatively low DM content of luminous dSphs such as Fornax and Leo I is due to tidal stripping, then their gravitational potential must be substantially more spherical than that of more heavily DM dominated systems such as Draco or Carina. The model also predicts a tidally-induced statistical excess of satellites whose major axis aligns with the direction to the central galaxy. Find evidence of this in the M31 satellite population, which suggest that tides may have played an important role in its evolution.
1410.6169
Early flattening of dark matter cusps in dwarf spheroidal galaxies
Nipoti, BInney
Simulations of the clustering of CDM yield DM haloes that have central density cusps, but observations of totally DM dominated dSph imply that they do not have cusp central density profiles. Use analytic calculations and numerical modeling to argue that whenever stars form, central density cups are likely to be erased. Gas that accumulates in the potential well of an initially cuspy DM halo settles into a disc. Eventually the surface density of the gas exceeds the threshold for fragmentation into self-gravitating clouds. The clouds are massive enough to transfer energy to the DM particles via dynamical friction on a short time-scale. The halo's central cusp is heated to form a core with central logarithmic density slope gamma=0 before stellar feedback makes its impact. Since star formation is an inefficient process, the clouds are disrupted by feedback when only a small fraction of their mass has been converted to stars, and the DM dominates the final mass distribution.
1410.6161
Galactic tides and the shape and orientation of dwarf galaxy satellites
Barber, Starkenburg, Navarro, McConnachie
Use cosmo N-body sims from Aquarius to study the tidal effects of a dark matter halo on the shape and orientation of its substructure. Although tides are often assumed to enhance sphericity and to stretch sub haloes tangentially, these effects are short lived: as in earlier work, find that sub haloes affected by tides become substantially more spherical and show a strong radial alignment toward the center of the host halo. These results, combined with SAM of galaxy formation, may be used to assess the effect of Galactic tides on the observed population of dSph satellites of the MW and Andromeda galaxies. If the relatively low DM content of luminous dSphs such as Fornax and Leo I is due to tidal stripping, then their gravitational potential must be substantially more spherical than that of more heavily DM dominated systems such as Draco or Carina. The model also predicts a tidally-induced statistical excess of satellites whose major axis aligns with the direction to the central galaxy. Find evidence of this in the M31 satellite population, which suggest that tides may have played an important role in its evolution.
1410.6169
Early flattening of dark matter cusps in dwarf spheroidal galaxies
Nipoti, BInney
Simulations of the clustering of CDM yield DM haloes that have central density cusps, but observations of totally DM dominated dSph imply that they do not have cusp central density profiles. Use analytic calculations and numerical modeling to argue that whenever stars form, central density cups are likely to be erased. Gas that accumulates in the potential well of an initially cuspy DM halo settles into a disc. Eventually the surface density of the gas exceeds the threshold for fragmentation into self-gravitating clouds. The clouds are massive enough to transfer energy to the DM particles via dynamical friction on a short time-scale. The halo's central cusp is heated to form a core with central logarithmic density slope gamma=0 before stellar feedback makes its impact. Since star formation is an inefficient process, the clouds are disrupted by feedback when only a small fraction of their mass has been converted to stars, and the DM dominates the final mass distribution.
Thursday, October 23, 2014
Day 770
Thursday. Friday.
1410.5812
Gas around galaxy haloes: methodology comparisons using hydrodynamical simulations of the intergalactic medium
Meiskin, Bolton, Tittley
IGM cosmo hydro sim at z~3 (GADGET-3 and Enzo) to model the gaseous environments of galaxies. Identify haloes in the simulations using 3 different algorithms. Different rank orderings of the haloes by mass result, introducing a limiting factor in identifying haloes with observed galaxies. Also compare the physical properties of the gas between the two codes, focussing primarily on the gas outside the viral radius, motivated by recent HI absorption measurements of the gas around z~ 2-3 galaxies. The internal dispersion velocities of the gas in the haloes have converged for a box size of 30 comoving Mpc, but the CoM peculiar velocities of the haloes have not up to a box size of 60 comoving Mpc. The density and temperature of the gas within the instantaneous turn-around radii of the haloes are adequately captured for box sizes 30 Mpc on a side, but the results are highly sensitive to the treatment of unresolved, rapidly cooling gas, with the gas mass fraction within the viral radius severely depleted by SF in the GADGET-3 simulations Convergence of the gas peculiar velocity field on large scales requires a box size of a least 60 Mpc. Outside the turn-around radius, the physical state of the gas agrees to 30% or better both with box size and between simulation methods. Conclude that generic IGM simulations make accurate predictions for the intergalactic gas properties beyond the halo turn-around radii, but the gas properties on smaller scales are highly dependent on SF and feedback implementations.
1410.5814
Possible signature of distant foreground in the Planck data
Yershov, Orlov, Raikov
Checked and confirmed the existence of a correlation between SN redshifts, z_SN, and CMB temperature fluctuations at the SNe locations, T_SN, which was reported for WMAP, and now seen in Planck map. 5sigma significance. Correlation becomes even stronger for SNe Ia, but vanishes for other types. Excluded the possibility of this anomaly being caused by SZ effect. Remaining possibility is some, unaccounted for, contribution to the CMB from z>0.3 FG though either ISW or thermal emission from IGM.
1410.5817
The dark matter haloes of moderate luminosity X-ray AGN as determined from weak gravitational lensing and host stellar masses
Leauthaud, et al
Show that better constraints of AGN and DM halo relation can be achieved through a rigorous comparison of the clustering, lensing, and cross-correlation signals of AGN hosts to a fiducial stellar-to-halo mass relation (SMHR) derived for all galaxies. The technique exploits the fact that the global SHMR can be measured with much higher accuracy than any statistic derived from AGN samples alone. Using 382 moderate luminosity X-ray AGN at z<1 from the COSMOS field, report the first measurements of weak gravitational lensing from an X-ray selected sample. Comparing this signal to predictions from the global SHMR, find that contrary to previous results, most X-ray AGN do not live in medium size groups - nearly half reside in relatively low mass haloes with Mh~1e12.5 Msun. The AGN occupation function is well described by the same form derived for all galaxies but with a lower normalization - the fraction of haloes with AGN in the sample is a few percent. By highlighting the relatively "normal" way in which moderate luminosity X-ray AGN hosts occupy haloes, the results suggest that the environmental signature of distinct fueling modes for luminous QSOs compared to moderate luminosity X-ray AGN is less obvious than previously claimed.
1410.6050
Comparing gravitational redshifts of SDSS galaxy clusters with the magnification redshift enhancement of background BOSS galaxies
Jimeno, Broadhurst, Coupon, Umetsu, Lazkoz
A clean measurement of the evolution of the galaxy cluster MF can significantly improve the understanding of cosmology from the rapid growth of cluster masses below z<0.5. Examine the consistency of cluster catalogs selected from the SDSS by applying two independent gravity-based methods using all available spectroscopic z from the DR10 release. First, detect a gravitational z related signal for 20k and 13k clusters with spec z contained in the GMBCG and redMaPPer catalogues, at a level of ~-10 km/s. This is consistent with the magnitude expected using richness-mass relations provided by the literature and after applying recently clarified relativistic and flux bias corrections. This signal is also consistent with the richest clusters in the larger catalogue of Wen+2012, corresponding to M_200m>2e14 Msun/h, however find no significant detection of gravitational redshift signal for less rich clusters, which may be related to bulk motions from substructure and serious cluster detections. Second, find all three catalogues generate mass-dependent levels of lensing magnification bias, which enhances the mean redshift of flux-selected BG galaxies from the BOSS survey. The magnitude of this lensing effect is generally consistent with the corresponding richness-mass relations advocated for the surveys. Conclude that all catalogues comprise a high proportion of reliable clusters, and that the CMBCG and redMaPPer cluster finder algorithms favor more relaxed clusters with a meaningful gravitational redshift signal, as anticipated by the red-sequence color selection of the GMBCG and redMaPPer samples.
1410.5812
Gas around galaxy haloes: methodology comparisons using hydrodynamical simulations of the intergalactic medium
Meiskin, Bolton, Tittley
IGM cosmo hydro sim at z~3 (GADGET-3 and Enzo) to model the gaseous environments of galaxies. Identify haloes in the simulations using 3 different algorithms. Different rank orderings of the haloes by mass result, introducing a limiting factor in identifying haloes with observed galaxies. Also compare the physical properties of the gas between the two codes, focussing primarily on the gas outside the viral radius, motivated by recent HI absorption measurements of the gas around z~ 2-3 galaxies. The internal dispersion velocities of the gas in the haloes have converged for a box size of 30 comoving Mpc, but the CoM peculiar velocities of the haloes have not up to a box size of 60 comoving Mpc. The density and temperature of the gas within the instantaneous turn-around radii of the haloes are adequately captured for box sizes 30 Mpc on a side, but the results are highly sensitive to the treatment of unresolved, rapidly cooling gas, with the gas mass fraction within the viral radius severely depleted by SF in the GADGET-3 simulations Convergence of the gas peculiar velocity field on large scales requires a box size of a least 60 Mpc. Outside the turn-around radius, the physical state of the gas agrees to 30% or better both with box size and between simulation methods. Conclude that generic IGM simulations make accurate predictions for the intergalactic gas properties beyond the halo turn-around radii, but the gas properties on smaller scales are highly dependent on SF and feedback implementations.
1410.5814
Possible signature of distant foreground in the Planck data
Yershov, Orlov, Raikov
Checked and confirmed the existence of a correlation between SN redshifts, z_SN, and CMB temperature fluctuations at the SNe locations, T_SN, which was reported for WMAP, and now seen in Planck map. 5sigma significance. Correlation becomes even stronger for SNe Ia, but vanishes for other types. Excluded the possibility of this anomaly being caused by SZ effect. Remaining possibility is some, unaccounted for, contribution to the CMB from z>0.3 FG though either ISW or thermal emission from IGM.
1410.5817
The dark matter haloes of moderate luminosity X-ray AGN as determined from weak gravitational lensing and host stellar masses
Leauthaud, et al
Show that better constraints of AGN and DM halo relation can be achieved through a rigorous comparison of the clustering, lensing, and cross-correlation signals of AGN hosts to a fiducial stellar-to-halo mass relation (SMHR) derived for all galaxies. The technique exploits the fact that the global SHMR can be measured with much higher accuracy than any statistic derived from AGN samples alone. Using 382 moderate luminosity X-ray AGN at z<1 from the COSMOS field, report the first measurements of weak gravitational lensing from an X-ray selected sample. Comparing this signal to predictions from the global SHMR, find that contrary to previous results, most X-ray AGN do not live in medium size groups - nearly half reside in relatively low mass haloes with Mh~1e12.5 Msun. The AGN occupation function is well described by the same form derived for all galaxies but with a lower normalization - the fraction of haloes with AGN in the sample is a few percent. By highlighting the relatively "normal" way in which moderate luminosity X-ray AGN hosts occupy haloes, the results suggest that the environmental signature of distinct fueling modes for luminous QSOs compared to moderate luminosity X-ray AGN is less obvious than previously claimed.
1410.6050
Comparing gravitational redshifts of SDSS galaxy clusters with the magnification redshift enhancement of background BOSS galaxies
Jimeno, Broadhurst, Coupon, Umetsu, Lazkoz
A clean measurement of the evolution of the galaxy cluster MF can significantly improve the understanding of cosmology from the rapid growth of cluster masses below z<0.5. Examine the consistency of cluster catalogs selected from the SDSS by applying two independent gravity-based methods using all available spectroscopic z from the DR10 release. First, detect a gravitational z related signal for 20k and 13k clusters with spec z contained in the GMBCG and redMaPPer catalogues, at a level of ~-10 km/s. This is consistent with the magnitude expected using richness-mass relations provided by the literature and after applying recently clarified relativistic and flux bias corrections. This signal is also consistent with the richest clusters in the larger catalogue of Wen+2012, corresponding to M_200m>2e14 Msun/h, however find no significant detection of gravitational redshift signal for less rich clusters, which may be related to bulk motions from substructure and serious cluster detections. Second, find all three catalogues generate mass-dependent levels of lensing magnification bias, which enhances the mean redshift of flux-selected BG galaxies from the BOSS survey. The magnitude of this lensing effect is generally consistent with the corresponding richness-mass relations advocated for the surveys. Conclude that all catalogues comprise a high proportion of reliable clusters, and that the CMBCG and redMaPPer cluster finder algorithms favor more relaxed clusters with a meaningful gravitational redshift signal, as anticipated by the red-sequence color selection of the GMBCG and redMaPPer samples.
Wednesday, October 22, 2014
Day 769
Wednesday.
1410.5425
The impact of feedback on cosmological gas accretion
Nelson, Genel, Vogelsberger, Springel, Sijacki, Torrey, Hernquist
Compare cosmo hydro sims with and without feedback, both with the moving mesh code AREPO. The feedback runs implement the full physics model of the Illustrious simulation project, including SF driven galactic winds and energetic feedback from SMBH. Explore (a) the accretion rate of material contributing to the net growth of galaxies and originating directly from the IGM, finding that feedback strongly suppresses the raw, as well as the net, inflow of this "smooth mode" gas at all z, regardless of the temperature history of newly acquired gas. (b) At the viral radius the temperature and radial flux of inflowing gas is largely unaffected at z=2. However, the spherical covering fraction of inflowing gas at 0.25 rvir decreases substantially, from more than 80% to less than 50%, while the rates of both inflow and outflow increase, indicative of recycling across this boundary. (c) The fractional contribution of smooth accretion to the total accretion rate is lower in the simulation with feedback, by roughly a factor of two across all redshifts. Moreover, the smooth component of gas with a cold temperature history, is entirely suppressed in the feedback run at z<1. (d) The amount of time taken by gas to cross from the viral radius to the galaxy - the "halo transit time" - increases in the presence of feedback by a factor of ~2-3, and is notably independent of halo mass. Discuss the possible implications of this invariance for theoretical models of hot halo gas cooling.
1410.5428
Extending the $L_{\mathrm{X}}-T$ relation from clusters to groups-Impact of cool core nature, AGN feedback, and selection effects
Bharadwaj, Reiprich, Lovisari, Eckmiller
Aim to investigate the bolometric L_X-T relation for galaxy groups, and study the impact of gas cooling, feedback from SMBHs, and selection effects on it. With a sample of 26 galaxy groups, obtain the best-fit L_X-T relation for 5 different cases depending on the ICM core properties and central AGN radio emission, and determined the slopes, normalizations, intrinsic and statistical scatters for both temperature and luminosity. Simulations were undertaken to correct for selection effects (e.g. Malmquist bias) and the bias corrected relations for groups and clusters were compared. The slope of the bias corrected L_X-T relation is marginally steeper but consistent with clusters (~3). Groups with a central cooling time less than 1Gyr (SCC groups) show indications of having the steepest slope and the highest normalization. For the groups, the bias corrected intrinsic scatter in L_X is larger than the observed scatter for most cases, which is reported here for the first time. Lastly, see indications that the groups with an extended central radio sources have a much steeper slope than those groups which have a CRS with only core emission. Additionally, also see indications that the more powerful radio AGN are preferentially located in NSCC groups rather than SCC groups.
1410.5429
First space-based microlens parallax measurement of an isolated star: Spitzer Observations of OGLE-2014-BLG-0939
Yee, ... Gould, et al
From the striking differences in the light curve as seen from Earth and from Spitzer (~1AU to the West), infer a projected velocity v_helio,pro ~240 km/s, which strongly favors a lens in the Galactic Disk with mass M=0.23pm0.07 Msun and distance D_L=3.1pm0.4 kpc. An ensemble of such measurements drawn from the ongoing program could be used to measure the single-lens mass function including dark objects, and also is necessary for measuring the Galactic distribution of planets since the ensemble reflects the underlying Galactic distribution of micro lenses. Study the application of the many ideas to break the four-fold degeneracy first predicted by Refsdal 50 years ago. Find that this degeneracy is clearly broken, but by two unanticipated mechanisms.
1410.5438
New constraints on $\sigma_8$ from a joint analysis of stacked gravitational lensing and clustering of galaxy clusters
Sereno, et al
Joint analysis of clustering and stacked gravitational lensing of galaxy clusters in large surveys can constrain the formation and evolution of structures and the cosmological parameters. On scales outside a few viral radii, the halo bias b is linear and the lensing signal is dominated by the correlated distribution of matter around galaxy clusters. Discuss a method to measure the PS amplitude sigma_8 and b based on a minimal modeling. Considered a sample of ~120k clusters photometrically selected from SDSS in 0.1<z<0.6. The auto-correlation was studied through the 2-pt function of a subsample of ~70k clusters; the matter-halo correlation was derived from the WL signal of the subsample of ~1200 clusters from CFHTLS. Obtained a direct measurement of b, which increases with mass in agreement with prediction of the LCDM paradigm. Assuming Omega_M=0.3, found sigma_8=0.78pm0.17. Used the same clusters for measuring both lensing and clustering, and the estimate of Sigma_8 did require neither the mass-richness relation, nor the knowledge of the selection function, nor the modeling of b. With an additional theoretical prior on the bias, obtain sigma_8=0.80pm0.10.
1410.5446
Masked areas in shear peak statistics: a forward modeling approach
Bard, Kratochvil, Dawson
The statistics of shear peaks have been shown to provide valuable cosmological info beyond the PS, and will be an important constant of models of cosmology with the large survey areas provided by forthcoming astronomical surveys. Surveys include masked areas due to bright stars, bad pixels etc, which must be accounted for in producing constraints on cosmology from shear maps. Advocate a forward-modeling approach, where the impact of masking (and other survey artifacts) are accounted for in the theoretical prediction of cosmo params, rather than removed from survey data. Use masks based on the DLS, and explore the impact of up to 37% of the survey area being masked on LSST and DES-scale surveys. By reconstructing maps of aperture mass, the masking effect is smoothed out, resulting in up to 14% smaller statistical uncertainties compared to simply reducing the survey area by the masked area. Show that, even in the presence of large survey masks, the bias in cosmo parameter estimation produced in the forward-modeling process is ~1%, dominated by bias caused by limited simulation volume. Also explore how this potential bias scales with survey area and find that small survey areas are more significantly impacted by the differences in cosmological structure in the data and simulated volumes, due to cosmic variance.
1410.5470
The formation of low-mass helium white dwarfs orbiting pulsars: evolution of low-mass X-ray binaries below the bifurcation period
Istrate, Tauris, Langer
Millisecond pulsars (MSPs) are generally believed to be old neutron stars (NSs) which have been spun up to high rotation rates via accretion of matter from a companion star in a LMXB. This scenario has been strongly supported by various pieces of observational evidence. However, many details of this recycling scenario remain to be understood. Investigate binary evolution in close LMXBs to sturdy the formation of radio MSPs with low-mass He WD companions in tight binaries with orbital periods P_orb=2-9 hr. In particular, examine i) if such observed systems can be reproduced from theoretical modeling using standard prescriptions of orbital angular momentum losses (i.e. with respect to the nature and the strength of magnetic breaking), ii) if the computations of the Roche-lobe detachments can match the observed orbital periods, and iii) if the correlation between WD mass and orbital period (M_WD, P_orb) is valid for systems with P_orb<2days. Numercial calculations with a detailed stellar evolution code were used to trace the mass-transfer phase in ~400 close LMXB systems with different initial values of donor star mass, NS mass, orbital period and the so-called gamma-index of magnetic breaking. Subsequently, follow the orbital and the interior evolution of the detached low-mass (proto) HE WDs, including stages with residual shell H burning. Find that a severe fine-tuning is necessary to reproduce the observed MSPs in tight binaries with He WD companions of mass <0.20 Msun, which suggests that something needs to be modified or is missing in the standard input physics of LMXB modeling. Results from previous independent studies support this conclusion. Demonstrate that the theoretically calculated (M_WD, P_orb)-relation is in general also valid for systems with P_orb<2days, although with a large scatter in He WD masses between 0.15-0.20 Msun. The results of the thermal evolution of the (proto) He WDs are reported in a follow-up paper (Paper II).
1410.5471
The timescale of low-mass proto-helium white dwarf evolution
Istrate, Tauris, Langer, Antoniadis
A large number of low-mass (<0.20 Msun) He WDs have recently been discovered. The majority of these are orbiting another WD or a millisecond pulsar (MSP) in a close binary system; a few examples are found to show pulsations or to have a main sequence star companion. There appears to be discrepancies between current theoretical modeling of such low-mass He WDs and a number of key observed cases, indicating that their formation scenario remains to be fully understood. Investigate the formation of detached proto-He WDs in close-orbit low-mass X-ray binaries (LMXBs). The prime focus is to examine the thermal evolution and the contraction phase towards the WD cooling track and investigate how this evolution depends on the WD mass. Calculations are then compared to the most recent observational data. Numerical calculations with a detailed stellar evolution code were used to trace the mass-transfer phase in a large number of close-orbit LMXBs with different initial values of donor star mass, neutron star mass, orbital period and strength of magnetic braking. Subsequently, follow the evolution of the detached low-mass proto-He WDs, including stages with residual shell hydrogen burning and vigorous flashes caused by unstable CNO burning. Find that the time between Roche-lobe detachment until the low-mass proto-He WD reaches the WD cooling track is typically Delta t_proto = 0.5-2 Gyr, depending systematically on the WD mass and therefore on its luminosity. The minimum WD mass for developing shell flashes is ~0.21 Msun for progenitor stars of mass M_2<1.5 Msun (and ~0.18 Msun for M_2=1.6 Msun) [why is shell flash important?]. The long timescale of low-mass proto-He WD evolution can explain a number of recent observations, including some MSP systems hosting He WD companions with very small surface gravities and high effective temperatures. Find no evidence for Delta t_proto to depend on the occurrence of flashes and thus question the suggested dichotomy in thermal evolution of proto-WDs.
1410.5425
The impact of feedback on cosmological gas accretion
Nelson, Genel, Vogelsberger, Springel, Sijacki, Torrey, Hernquist
Compare cosmo hydro sims with and without feedback, both with the moving mesh code AREPO. The feedback runs implement the full physics model of the Illustrious simulation project, including SF driven galactic winds and energetic feedback from SMBH. Explore (a) the accretion rate of material contributing to the net growth of galaxies and originating directly from the IGM, finding that feedback strongly suppresses the raw, as well as the net, inflow of this "smooth mode" gas at all z, regardless of the temperature history of newly acquired gas. (b) At the viral radius the temperature and radial flux of inflowing gas is largely unaffected at z=2. However, the spherical covering fraction of inflowing gas at 0.25 rvir decreases substantially, from more than 80% to less than 50%, while the rates of both inflow and outflow increase, indicative of recycling across this boundary. (c) The fractional contribution of smooth accretion to the total accretion rate is lower in the simulation with feedback, by roughly a factor of two across all redshifts. Moreover, the smooth component of gas with a cold temperature history, is entirely suppressed in the feedback run at z<1. (d) The amount of time taken by gas to cross from the viral radius to the galaxy - the "halo transit time" - increases in the presence of feedback by a factor of ~2-3, and is notably independent of halo mass. Discuss the possible implications of this invariance for theoretical models of hot halo gas cooling.
1410.5428
Extending the $L_{\mathrm{X}}-T$ relation from clusters to groups-Impact of cool core nature, AGN feedback, and selection effects
Bharadwaj, Reiprich, Lovisari, Eckmiller
Aim to investigate the bolometric L_X-T relation for galaxy groups, and study the impact of gas cooling, feedback from SMBHs, and selection effects on it. With a sample of 26 galaxy groups, obtain the best-fit L_X-T relation for 5 different cases depending on the ICM core properties and central AGN radio emission, and determined the slopes, normalizations, intrinsic and statistical scatters for both temperature and luminosity. Simulations were undertaken to correct for selection effects (e.g. Malmquist bias) and the bias corrected relations for groups and clusters were compared. The slope of the bias corrected L_X-T relation is marginally steeper but consistent with clusters (~3). Groups with a central cooling time less than 1Gyr (SCC groups) show indications of having the steepest slope and the highest normalization. For the groups, the bias corrected intrinsic scatter in L_X is larger than the observed scatter for most cases, which is reported here for the first time. Lastly, see indications that the groups with an extended central radio sources have a much steeper slope than those groups which have a CRS with only core emission. Additionally, also see indications that the more powerful radio AGN are preferentially located in NSCC groups rather than SCC groups.
1410.5429
First space-based microlens parallax measurement of an isolated star: Spitzer Observations of OGLE-2014-BLG-0939
Yee, ... Gould, et al
From the striking differences in the light curve as seen from Earth and from Spitzer (~1AU to the West), infer a projected velocity v_helio,pro ~240 km/s, which strongly favors a lens in the Galactic Disk with mass M=0.23pm0.07 Msun and distance D_L=3.1pm0.4 kpc. An ensemble of such measurements drawn from the ongoing program could be used to measure the single-lens mass function including dark objects, and also is necessary for measuring the Galactic distribution of planets since the ensemble reflects the underlying Galactic distribution of micro lenses. Study the application of the many ideas to break the four-fold degeneracy first predicted by Refsdal 50 years ago. Find that this degeneracy is clearly broken, but by two unanticipated mechanisms.
1410.5438
New constraints on $\sigma_8$ from a joint analysis of stacked gravitational lensing and clustering of galaxy clusters
Sereno, et al
Joint analysis of clustering and stacked gravitational lensing of galaxy clusters in large surveys can constrain the formation and evolution of structures and the cosmological parameters. On scales outside a few viral radii, the halo bias b is linear and the lensing signal is dominated by the correlated distribution of matter around galaxy clusters. Discuss a method to measure the PS amplitude sigma_8 and b based on a minimal modeling. Considered a sample of ~120k clusters photometrically selected from SDSS in 0.1<z<0.6. The auto-correlation was studied through the 2-pt function of a subsample of ~70k clusters; the matter-halo correlation was derived from the WL signal of the subsample of ~1200 clusters from CFHTLS. Obtained a direct measurement of b, which increases with mass in agreement with prediction of the LCDM paradigm. Assuming Omega_M=0.3, found sigma_8=0.78pm0.17. Used the same clusters for measuring both lensing and clustering, and the estimate of Sigma_8 did require neither the mass-richness relation, nor the knowledge of the selection function, nor the modeling of b. With an additional theoretical prior on the bias, obtain sigma_8=0.80pm0.10.
1410.5446
Masked areas in shear peak statistics: a forward modeling approach
Bard, Kratochvil, Dawson
The statistics of shear peaks have been shown to provide valuable cosmological info beyond the PS, and will be an important constant of models of cosmology with the large survey areas provided by forthcoming astronomical surveys. Surveys include masked areas due to bright stars, bad pixels etc, which must be accounted for in producing constraints on cosmology from shear maps. Advocate a forward-modeling approach, where the impact of masking (and other survey artifacts) are accounted for in the theoretical prediction of cosmo params, rather than removed from survey data. Use masks based on the DLS, and explore the impact of up to 37% of the survey area being masked on LSST and DES-scale surveys. By reconstructing maps of aperture mass, the masking effect is smoothed out, resulting in up to 14% smaller statistical uncertainties compared to simply reducing the survey area by the masked area. Show that, even in the presence of large survey masks, the bias in cosmo parameter estimation produced in the forward-modeling process is ~1%, dominated by bias caused by limited simulation volume. Also explore how this potential bias scales with survey area and find that small survey areas are more significantly impacted by the differences in cosmological structure in the data and simulated volumes, due to cosmic variance.
1410.5470
The formation of low-mass helium white dwarfs orbiting pulsars: evolution of low-mass X-ray binaries below the bifurcation period
Istrate, Tauris, Langer
Millisecond pulsars (MSPs) are generally believed to be old neutron stars (NSs) which have been spun up to high rotation rates via accretion of matter from a companion star in a LMXB. This scenario has been strongly supported by various pieces of observational evidence. However, many details of this recycling scenario remain to be understood. Investigate binary evolution in close LMXBs to sturdy the formation of radio MSPs with low-mass He WD companions in tight binaries with orbital periods P_orb=2-9 hr. In particular, examine i) if such observed systems can be reproduced from theoretical modeling using standard prescriptions of orbital angular momentum losses (i.e. with respect to the nature and the strength of magnetic breaking), ii) if the computations of the Roche-lobe detachments can match the observed orbital periods, and iii) if the correlation between WD mass and orbital period (M_WD, P_orb) is valid for systems with P_orb<2days. Numercial calculations with a detailed stellar evolution code were used to trace the mass-transfer phase in ~400 close LMXB systems with different initial values of donor star mass, NS mass, orbital period and the so-called gamma-index of magnetic breaking. Subsequently, follow the orbital and the interior evolution of the detached low-mass (proto) HE WDs, including stages with residual shell H burning. Find that a severe fine-tuning is necessary to reproduce the observed MSPs in tight binaries with He WD companions of mass <0.20 Msun, which suggests that something needs to be modified or is missing in the standard input physics of LMXB modeling. Results from previous independent studies support this conclusion. Demonstrate that the theoretically calculated (M_WD, P_orb)-relation is in general also valid for systems with P_orb<2days, although with a large scatter in He WD masses between 0.15-0.20 Msun. The results of the thermal evolution of the (proto) He WDs are reported in a follow-up paper (Paper II).
1410.5471
The timescale of low-mass proto-helium white dwarf evolution
Istrate, Tauris, Langer, Antoniadis
A large number of low-mass (<0.20 Msun) He WDs have recently been discovered. The majority of these are orbiting another WD or a millisecond pulsar (MSP) in a close binary system; a few examples are found to show pulsations or to have a main sequence star companion. There appears to be discrepancies between current theoretical modeling of such low-mass He WDs and a number of key observed cases, indicating that their formation scenario remains to be fully understood. Investigate the formation of detached proto-He WDs in close-orbit low-mass X-ray binaries (LMXBs). The prime focus is to examine the thermal evolution and the contraction phase towards the WD cooling track and investigate how this evolution depends on the WD mass. Calculations are then compared to the most recent observational data. Numerical calculations with a detailed stellar evolution code were used to trace the mass-transfer phase in a large number of close-orbit LMXBs with different initial values of donor star mass, neutron star mass, orbital period and strength of magnetic braking. Subsequently, follow the evolution of the detached low-mass proto-He WDs, including stages with residual shell hydrogen burning and vigorous flashes caused by unstable CNO burning. Find that the time between Roche-lobe detachment until the low-mass proto-He WD reaches the WD cooling track is typically Delta t_proto = 0.5-2 Gyr, depending systematically on the WD mass and therefore on its luminosity. The minimum WD mass for developing shell flashes is ~0.21 Msun for progenitor stars of mass M_2<1.5 Msun (and ~0.18 Msun for M_2=1.6 Msun) [why is shell flash important?]. The long timescale of low-mass proto-He WD evolution can explain a number of recent observations, including some MSP systems hosting He WD companions with very small surface gravities and high effective temperatures. Find no evidence for Delta t_proto to depend on the occurrence of flashes and thus question the suggested dichotomy in thermal evolution of proto-WDs.
Monday, October 20, 2014
Day 768
Tuesday.
1410.4937
Galaxy stellar mass assembly: the difficulty to match observations and semi-analytical predictions
Cousin, et al
SAMs are currently the best way to understand the formation of galaxies within the cosmic DM structures. While they fairly well reproduce the local stellar MFs, correlation functions and LFs, they fail to match observations at high z (>3) in most cases, particularly in the low-mass range. The inconsistency between models and observations indicates that the history of gas accretion in galaxies, within their host DM halo, and the transformation of gas into stars, are not well followed. Briefly present a new version of the GalICS SAM. Explore the impacts of classical mechanisms, such as SNe feedback or photoionization, on the evolution of the stellar mass assembly. Even with a strong efficiency, these two processes cannot explain the observed stellar MF and SFR distribution and some other relations. Thus introduce an ad-hoc modification of the standard paradigm, based on the presence of a no-SF gas component, and a concentration of the SF gas in galaxy disks. The main idea behind the existence of the no-SF gas reservoir is that only a fraction of the total gas mass in a galaxy is available to form stars. The reservoir generates a delay between the accretion of the gas and the SF process. This new model is in much better agreement with the observations of the stellar MF in the low-mass range than the previous models, and agrees quite well with a large set of observations, including the z evolution of the sSFR. However, it predicts a large fraction of no-SF baryonic gas, potentially larger than observed, even if its nature has still to be examined in the context of the missing baryon problem.
1410.4997
Evidence of cross-correlation between the CMB lensing and the gamma-ray sky
Fornengo et al
3.2 sigma, in correlation with Planck CMB lensing map.
1410.4937
Galaxy stellar mass assembly: the difficulty to match observations and semi-analytical predictions
Cousin, et al
SAMs are currently the best way to understand the formation of galaxies within the cosmic DM structures. While they fairly well reproduce the local stellar MFs, correlation functions and LFs, they fail to match observations at high z (>3) in most cases, particularly in the low-mass range. The inconsistency between models and observations indicates that the history of gas accretion in galaxies, within their host DM halo, and the transformation of gas into stars, are not well followed. Briefly present a new version of the GalICS SAM. Explore the impacts of classical mechanisms, such as SNe feedback or photoionization, on the evolution of the stellar mass assembly. Even with a strong efficiency, these two processes cannot explain the observed stellar MF and SFR distribution and some other relations. Thus introduce an ad-hoc modification of the standard paradigm, based on the presence of a no-SF gas component, and a concentration of the SF gas in galaxy disks. The main idea behind the existence of the no-SF gas reservoir is that only a fraction of the total gas mass in a galaxy is available to form stars. The reservoir generates a delay between the accretion of the gas and the SF process. This new model is in much better agreement with the observations of the stellar MF in the low-mass range than the previous models, and agrees quite well with a large set of observations, including the z evolution of the sSFR. However, it predicts a large fraction of no-SF baryonic gas, potentially larger than observed, even if its nature has still to be examined in the context of the missing baryon problem.
1410.4997
Evidence of cross-correlation between the CMB lensing and the gamma-ray sky
Fornengo et al
3.2 sigma, in correlation with Planck CMB lensing map.
Sunday, October 19, 2014
Day 767
Monday.
1410.4559
Tow new methods to detect cosmic voids without density measurements
Elyiv, ... Branchini, etal
Two new void finders based on dynamical and clustering criteria to select voids in Lagrangian coordinates and minimize the impact of sparse sampling. The first approach exploits the Zeldovich approximation to trace back in time the orbits of galaxies located in the voids and their surroundings, whereas the second uses the observed gg correlation function to relax the objects' spatial distribution to homogeneity and isotropy. In both cases voids are defined as regions of the negative velocity divergence in Lagrangian coordinates, that can be regarded as sinks of the back-in-time streamlines of the mass tracers. To assess the performance of the methods, use a DM halo catalogue extracted from an N-body simulation at z=0, and compared the results with those obtained with ZOBOV void finder. Find that the void divergence profiles are less scattered than the density ones, so their stacking constitutes a more accurate cosmological probe. The significance of the divergence signal in the central part of voids obtained from both finders is 60% higher than for overdensity profiles in the ZOBOV case. Individual voids selected by both finders have similar tri-axial ellipsoidal shapes. The ellipticity of the stacked void measured in the divergence field is significantly closer to unity, as expected, than what is found when using halo positions. These results show that the new void finders are complementary to the existing methods, that should contribute to improve the accuracy of void-based cosmological tests.
1410.4565
Data mining for gravitationally lensed quasars
Agnello, Kelly, Treu, Marshall
A systematic exploration of machine learning techniques and demonstrate that a two step strategy can be highly effective. In the first step, use catalog-level information (griz+WISE magnitudes, second moments) to preselect targets, using artificial neural networks. The accepted targets are them inspected with pixel-by-pixel pattern recognition algorithms (Gradien-Boosted Trees), to form a final set of candidates. The results from this procedure can be used to further refine the simpler SQLS algorithms, with a 2x (or 3x) gain in purity and the same (or 80%) completeness at target-selection stage, or a purity of 70% and a completeness of 60% after the candidate-selection step. Simpler photometric searches in griz+WISE based on color cuts would provide samples with 7 purity or less. The technique is extremely fast, as a list of candidates can be obtained from a stage III experiment (e.g. DES catalog/database) in a few CPU hours. The techniques are easily extendable to Stage IV experiments like LSST with the addition of time domain information.
1410.4568
The mass-concentration relation in lensing clusters: the role of statistical biases and selection effects
Sereno, Giocoli, Ettori, Moscardini
The relation between mass and concentration of galaxy clusters traces their formation and evolution. Massive lensing clusters were observed to be over-concentrated and following a steeper scaling in tension with predictions from standard LCDM. Critically revise the relation in the CLASH, SGAS, LOCUSS and a high-z sample of WL clusters. Measurements of mass and concentration are anti-correlated, which can bias the observed relation towards steeper values. Corrected for this bias and compared the measured relation to theoretical predictions accounting for halo triaxiality, adiabatic contraction of the halo, presence of a dominant BCG and, mostly, select effects in the observed sample. The normalization, the slope and the scatter of the expected relation are strongly sample-dependent. For the considered samples, the predicted slope is much steeper than that of the underlying relation characterizing DM only cluster. Find that correction of the statistical and selection biases mostly solve the tension with the LCDM model.
1410.4696
Feature importance for machine learning redshifts applied to SDSS galaxies
Hoyle, et al
Present an analysis of importance feature selection applied to photometric redshift estimation using the machine learning architecture Random Decision Forests (RDF) with the ensemble learning routing Adaboost. Select a list of 85 easily measured (or derived) photometric quantities (or 'features') and spectroscopic redshifts for almost 2e6 galaxies from SDSS DR10. After identifying which features have the most predictive power, use standard artificial Neural Networks (aNN) to show that the addition of these features, in combination with the standard magnitudes and colors, improves the machine learning redshift estimate by 18% and decrease the catastrophic outlier rate by 32%. Further compare the redshift estimate from RDF using the ensemble learning routine Adaboost with those from two different aNNs, and with photometric redshifts available from the SDSS. Find that the RDF requires orders of magnitude less computation time than the aNNs to obtain a machine learning redshift while reducing both the catastrophic outlier rate by put to 43%, and the redshift error by up to 25%. When compared to the SDSS photo-z, the RDF machine learning redshifts both decreases the standard deviation of residuals scaled by 1/(1+z) by 36% from 0.066 to 0.041, and decreases the fraction of catastrophic outliers by 57% from 2.32% to 0.99%.
1410.4559
Tow new methods to detect cosmic voids without density measurements
Elyiv, ... Branchini, etal
Two new void finders based on dynamical and clustering criteria to select voids in Lagrangian coordinates and minimize the impact of sparse sampling. The first approach exploits the Zeldovich approximation to trace back in time the orbits of galaxies located in the voids and their surroundings, whereas the second uses the observed gg correlation function to relax the objects' spatial distribution to homogeneity and isotropy. In both cases voids are defined as regions of the negative velocity divergence in Lagrangian coordinates, that can be regarded as sinks of the back-in-time streamlines of the mass tracers. To assess the performance of the methods, use a DM halo catalogue extracted from an N-body simulation at z=0, and compared the results with those obtained with ZOBOV void finder. Find that the void divergence profiles are less scattered than the density ones, so their stacking constitutes a more accurate cosmological probe. The significance of the divergence signal in the central part of voids obtained from both finders is 60% higher than for overdensity profiles in the ZOBOV case. Individual voids selected by both finders have similar tri-axial ellipsoidal shapes. The ellipticity of the stacked void measured in the divergence field is significantly closer to unity, as expected, than what is found when using halo positions. These results show that the new void finders are complementary to the existing methods, that should contribute to improve the accuracy of void-based cosmological tests.
1410.4565
Data mining for gravitationally lensed quasars
Agnello, Kelly, Treu, Marshall
A systematic exploration of machine learning techniques and demonstrate that a two step strategy can be highly effective. In the first step, use catalog-level information (griz+WISE magnitudes, second moments) to preselect targets, using artificial neural networks. The accepted targets are them inspected with pixel-by-pixel pattern recognition algorithms (Gradien-Boosted Trees), to form a final set of candidates. The results from this procedure can be used to further refine the simpler SQLS algorithms, with a 2x (or 3x) gain in purity and the same (or 80%) completeness at target-selection stage, or a purity of 70% and a completeness of 60% after the candidate-selection step. Simpler photometric searches in griz+WISE based on color cuts would provide samples with 7 purity or less. The technique is extremely fast, as a list of candidates can be obtained from a stage III experiment (e.g. DES catalog/database) in a few CPU hours. The techniques are easily extendable to Stage IV experiments like LSST with the addition of time domain information.
1410.4568
The mass-concentration relation in lensing clusters: the role of statistical biases and selection effects
Sereno, Giocoli, Ettori, Moscardini
The relation between mass and concentration of galaxy clusters traces their formation and evolution. Massive lensing clusters were observed to be over-concentrated and following a steeper scaling in tension with predictions from standard LCDM. Critically revise the relation in the CLASH, SGAS, LOCUSS and a high-z sample of WL clusters. Measurements of mass and concentration are anti-correlated, which can bias the observed relation towards steeper values. Corrected for this bias and compared the measured relation to theoretical predictions accounting for halo triaxiality, adiabatic contraction of the halo, presence of a dominant BCG and, mostly, select effects in the observed sample. The normalization, the slope and the scatter of the expected relation are strongly sample-dependent. For the considered samples, the predicted slope is much steeper than that of the underlying relation characterizing DM only cluster. Find that correction of the statistical and selection biases mostly solve the tension with the LCDM model.
1410.4696
Feature importance for machine learning redshifts applied to SDSS galaxies
Hoyle, et al
Present an analysis of importance feature selection applied to photometric redshift estimation using the machine learning architecture Random Decision Forests (RDF) with the ensemble learning routing Adaboost. Select a list of 85 easily measured (or derived) photometric quantities (or 'features') and spectroscopic redshifts for almost 2e6 galaxies from SDSS DR10. After identifying which features have the most predictive power, use standard artificial Neural Networks (aNN) to show that the addition of these features, in combination with the standard magnitudes and colors, improves the machine learning redshift estimate by 18% and decrease the catastrophic outlier rate by 32%. Further compare the redshift estimate from RDF using the ensemble learning routine Adaboost with those from two different aNNs, and with photometric redshifts available from the SDSS. Find that the RDF requires orders of magnitude less computation time than the aNNs to obtain a machine learning redshift while reducing both the catastrophic outlier rate by put to 43%, and the redshift error by up to 25%. When compared to the SDSS photo-z, the RDF machine learning redshifts both decreases the standard deviation of residuals scaled by 1/(1+z) by 36% from 0.066 to 0.041, and decreases the fraction of catastrophic outliers by 57% from 2.32% to 0.99%.
Thursday, October 16, 2014
Day 766
Friday.
1410.4270
Galaxy alignment on large and small scales
Kang, et al
On small scales satellite galaxies have a tendency to distribute along the major axis of the central galaxy, with dependence on galaxy properties that both red satellites and centrals have stronger alignment than their blue counterparts. On large scales, it is found that the major axes of LRGs have correlation up to 30 Mpc/h. Using hydro-dynamical sim with SF, investigate the origin of galaxy alignment on different scales. Found that most red satellite galaxies stay in the inner region of DM halo inside which the shape of the central galaxy is well aligned with the DM distribution. Red centrals have stronger alignment than blue ones as they live in massive haloes and the central galaxy-halo alignment increases with halo mass. On large scales, the alignment of LRGs is also from the galaxy-halo shape correlation, but with some extent of mis-alignment. The massive haloes have stronger alignment than haloes in filament which connect massive haloes. This is contrary to the naive expectation that cosmic filament is the cause of halo alignment.
1410.4502
Cross-correlation between the CMB lensing potential measured by Planck and high-z sub-mm galaxies detected by the Herschel-ATLAS survey
Bianchini, et al
Correlation between CMB lensing from Planck and z>1.5 galaxies from Herschel-ATLAS covering 600 sq deg. 20sigma correlation found, substantially stronger than expected. The result was checked by performing a number of null tests. The galaxy bias parameter, b, derived from a joint analysis of the cross-power spectrum and of the auto-power spectrum of the galaxy density contrast is found to be b=2.8, consistent with earlier estimates of H-ATLAS galaxies at similar redshifts. On the other hand, the amplitude of the cross-correlation is found to be a factor 1.6 higher than expected from the standard model and also found by cross-correlation analysis with other tracers of the LSS. The enhancement due to lensing magnification can account for only a fraction of the excess X-correlation signal. Suggest that most of it may be due to an incomplete removal of the contamination of the CIB, that includes the H-ATLAS sources that are being X-correlated with. In any case, the highly significant detection reported here using a catalog covering only 1.5% of the sky demonstrates the potential of CMB lensing correlations with sub-mm surveys.
1410.4270
Galaxy alignment on large and small scales
Kang, et al
On small scales satellite galaxies have a tendency to distribute along the major axis of the central galaxy, with dependence on galaxy properties that both red satellites and centrals have stronger alignment than their blue counterparts. On large scales, it is found that the major axes of LRGs have correlation up to 30 Mpc/h. Using hydro-dynamical sim with SF, investigate the origin of galaxy alignment on different scales. Found that most red satellite galaxies stay in the inner region of DM halo inside which the shape of the central galaxy is well aligned with the DM distribution. Red centrals have stronger alignment than blue ones as they live in massive haloes and the central galaxy-halo alignment increases with halo mass. On large scales, the alignment of LRGs is also from the galaxy-halo shape correlation, but with some extent of mis-alignment. The massive haloes have stronger alignment than haloes in filament which connect massive haloes. This is contrary to the naive expectation that cosmic filament is the cause of halo alignment.
1410.4502
Cross-correlation between the CMB lensing potential measured by Planck and high-z sub-mm galaxies detected by the Herschel-ATLAS survey
Bianchini, et al
Correlation between CMB lensing from Planck and z>1.5 galaxies from Herschel-ATLAS covering 600 sq deg. 20sigma correlation found, substantially stronger than expected. The result was checked by performing a number of null tests. The galaxy bias parameter, b, derived from a joint analysis of the cross-power spectrum and of the auto-power spectrum of the galaxy density contrast is found to be b=2.8, consistent with earlier estimates of H-ATLAS galaxies at similar redshifts. On the other hand, the amplitude of the cross-correlation is found to be a factor 1.6 higher than expected from the standard model and also found by cross-correlation analysis with other tracers of the LSS. The enhancement due to lensing magnification can account for only a fraction of the excess X-correlation signal. Suggest that most of it may be due to an incomplete removal of the contamination of the CIB, that includes the H-ATLAS sources that are being X-correlated with. In any case, the highly significant detection reported here using a catalog covering only 1.5% of the sky demonstrates the potential of CMB lensing correlations with sub-mm surveys.
Wednesday, October 15, 2014
Day 765
Thursday.
1410.3883
Comparing dense galaxy cluster redshift surveys with weak lensing maps
Hwang, Geller, et al
9 galaxy clusters at z~0.2; cover with spectroscopic samples within region of WL maps of high (70-89%) and uniform completeness. With these dense redshift surveys, construct galaxy number density maps using several galaxy subsamples. The shape of the main cluster concentration in the WL maps is similar to the global morphology of the number density maps based on cluster members alone, mainly dominated by red members. Cross correlate the galaxy number density maps with the WL maps. The cross correlation signal when FG and BG galaxies at 0.5 z_cl < z <2 z_cl is included is 10-23% larger than for cluster members alone at the cluster virial radius. The excess can be as high as 30% depending on the cluster. Cross correlating the galaxy number density and WL maps suggests that superimposed structures close to the cluster in z space contribute more significantly to the excess cross correlation signal than unrelated LSS along the LoS. The WL mass profiles are not well constrained for clusters with the largest cross correlation signal excesses (>20%). The fractional excess in the cross correlation signal including FG and BG structures could be a useful proxy for assessing the reliability of WL cluster mass estimates.
1410.4061
The origin of spin in galaxies: clues from simulations of atomic cooling halos
Prieto, Jiminez, Haiman, González
From Hydro sims from cosmological IC: The main conclusion is that the spin orientation and magnitude is initially well described by tidal torque linear theory, but later on is determined by the merging and accretion history of each halo. Provide evidence that the topology of the merging region, i.e., the number of colliding filaments, gives an accurate prediction for the spin of DM and gas: halos at the center of knots will have low spin while those in the center of filaments will have high spin.
1410.3883
Comparing dense galaxy cluster redshift surveys with weak lensing maps
Hwang, Geller, et al
9 galaxy clusters at z~0.2; cover with spectroscopic samples within region of WL maps of high (70-89%) and uniform completeness. With these dense redshift surveys, construct galaxy number density maps using several galaxy subsamples. The shape of the main cluster concentration in the WL maps is similar to the global morphology of the number density maps based on cluster members alone, mainly dominated by red members. Cross correlate the galaxy number density maps with the WL maps. The cross correlation signal when FG and BG galaxies at 0.5 z_cl < z <2 z_cl is included is 10-23% larger than for cluster members alone at the cluster virial radius. The excess can be as high as 30% depending on the cluster. Cross correlating the galaxy number density and WL maps suggests that superimposed structures close to the cluster in z space contribute more significantly to the excess cross correlation signal than unrelated LSS along the LoS. The WL mass profiles are not well constrained for clusters with the largest cross correlation signal excesses (>20%). The fractional excess in the cross correlation signal including FG and BG structures could be a useful proxy for assessing the reliability of WL cluster mass estimates.
1410.4061
The origin of spin in galaxies: clues from simulations of atomic cooling halos
Prieto, Jiminez, Haiman, González
From Hydro sims from cosmological IC: The main conclusion is that the spin orientation and magnitude is initially well described by tidal torque linear theory, but later on is determined by the merging and accretion history of each halo. Provide evidence that the topology of the merging region, i.e., the number of colliding filaments, gives an accurate prediction for the spin of DM and gas: halos at the center of knots will have low spin while those in the center of filaments will have high spin.
Tuesday, October 14, 2014
Day 764
Wednesday.
1410.3468
An exploration of galaxy-galaxy lensing and galaxy clustering in the Millennium-XL simulation
Marian, Smith, Angulo
The combination of gg lensing and galaxy clustering data has the potential to simultaneously constrain both the cosmological galaxy formation models. However, to fully exploit this potential one needs to understand the signals as well as their joint covariance matrix. In this paper, perform a comprehensive exploration of these ingredients, through a combination of analytic and numerical approaches. First, derive analytic expressions for the projected galaxy correlation function and stacked tangential shear profile and their respective covariances. Second, measure these quantitates from mock galaxy catalogues derived from the Millennium-XXL simulation and SAM of galaxy formation. Find that on large scales (R>10 Mpc), the galaxy bias is roughly linear and deterministic. On smaller scales (R<5Mpc) the bias is a complicated function of scale and luminosity, determined by the different spatial distribution and abundance of satellite galaxies present when different magnitude cuts are applied, as well as by the dependence of the mass of haloes hosting the central galaxies on magnitude. The theoretical model for the covariances provides a reasonably good description of the measured ones on small and large scales. However, on intermediate scales (1<R<10 Mpc), the predicted errors are ~2-3x smaller, suggesting that the inclusion of higher-order, non-Gaussian terms in the covariance will be required for further improvements. Importantly, both the theoretical and numerical methods show that the gg lensing and clustering signals are not independent from each other, but have a non-hero cross-covariance matrix with significant bin-to-bin correlation. Future surveys aiming to combine these probes must take this into account in order to obtain unbiased and realistic constraints.
1410.3489
The clustering of halo masses of star forming galaxies at z<1
Dolley, ... Kochanek, et al
Clustering measurements and halo masses of SF galaxies at 0.2<z<1.0. After excluding AGN, construct a sample of 22k 24um sources selected from 8.42 sq deg of Spityer MIPS AGN and Galaxy Evolution Survey of Boötes. MIR imaging allows observation of galaxies with the highest SFRs, less biased by dust obscuration afflicting the optical bands. Find that the galaxies with the highest SFRs have optical colors which are redder than typical blue cloud galaxies, with many residing within the green valley. At z>0.4, the sample is dominated by LIRGs, >1e11 Lsun) and is comprised entirely of LIRGs and ULRIGS (>1e12 Lsun) at z>0.6. Observe weak clustering of r_0=3-6 Mpc/h for almost all of the SF samples. Find that the clustering and halo mass depend on L at all redshifts, where galaxies with higher L (hence higher SFRs) have stronger clustering. Galaxies with the highest SFRs at each z typically reside within DM haloes of M~1e12.9 Msun/h. This is consistent with a transitional halo mass, above which SF is largely truncated, although cannot exclude that ULIRGs reside within higher mass haloes. By modeling the clustering evolution of haloes, connect the SF galaxy samples to their local descendants. Most SF galaxies at z<1.0 are the progenitors of L<2.5 L* blue galaxies in the local universe, but SF galaxies with the highest SFRs (>1e11.7 Lsun) at 0.6<z<1.0 are the progenitors of early-type galaxies in denser group environments.
1410.3468
An exploration of galaxy-galaxy lensing and galaxy clustering in the Millennium-XL simulation
Marian, Smith, Angulo
The combination of gg lensing and galaxy clustering data has the potential to simultaneously constrain both the cosmological galaxy formation models. However, to fully exploit this potential one needs to understand the signals as well as their joint covariance matrix. In this paper, perform a comprehensive exploration of these ingredients, through a combination of analytic and numerical approaches. First, derive analytic expressions for the projected galaxy correlation function and stacked tangential shear profile and their respective covariances. Second, measure these quantitates from mock galaxy catalogues derived from the Millennium-XXL simulation and SAM of galaxy formation. Find that on large scales (R>10 Mpc), the galaxy bias is roughly linear and deterministic. On smaller scales (R<5Mpc) the bias is a complicated function of scale and luminosity, determined by the different spatial distribution and abundance of satellite galaxies present when different magnitude cuts are applied, as well as by the dependence of the mass of haloes hosting the central galaxies on magnitude. The theoretical model for the covariances provides a reasonably good description of the measured ones on small and large scales. However, on intermediate scales (1<R<10 Mpc), the predicted errors are ~2-3x smaller, suggesting that the inclusion of higher-order, non-Gaussian terms in the covariance will be required for further improvements. Importantly, both the theoretical and numerical methods show that the gg lensing and clustering signals are not independent from each other, but have a non-hero cross-covariance matrix with significant bin-to-bin correlation. Future surveys aiming to combine these probes must take this into account in order to obtain unbiased and realistic constraints.
1410.3489
The clustering of halo masses of star forming galaxies at z<1
Dolley, ... Kochanek, et al
Clustering measurements and halo masses of SF galaxies at 0.2<z<1.0. After excluding AGN, construct a sample of 22k 24um sources selected from 8.42 sq deg of Spityer MIPS AGN and Galaxy Evolution Survey of Boötes. MIR imaging allows observation of galaxies with the highest SFRs, less biased by dust obscuration afflicting the optical bands. Find that the galaxies with the highest SFRs have optical colors which are redder than typical blue cloud galaxies, with many residing within the green valley. At z>0.4, the sample is dominated by LIRGs, >1e11 Lsun) and is comprised entirely of LIRGs and ULRIGS (>1e12 Lsun) at z>0.6. Observe weak clustering of r_0=3-6 Mpc/h for almost all of the SF samples. Find that the clustering and halo mass depend on L at all redshifts, where galaxies with higher L (hence higher SFRs) have stronger clustering. Galaxies with the highest SFRs at each z typically reside within DM haloes of M~1e12.9 Msun/h. This is consistent with a transitional halo mass, above which SF is largely truncated, although cannot exclude that ULIRGs reside within higher mass haloes. By modeling the clustering evolution of haloes, connect the SF galaxy samples to their local descendants. Most SF galaxies at z<1.0 are the progenitors of L<2.5 L* blue galaxies in the local universe, but SF galaxies with the highest SFRs (>1e11.7 Lsun) at 0.6<z<1.0 are the progenitors of early-type galaxies in denser group environments.
Monday, October 13, 2014
Day 763
Tuesday.
1410.2768
Origins of massive field stars in the galactic center: a spectroscopic study
Dong et al
A large number of evolved massive stars have been detected in the Galactic Center, outside the known star clusters; but their origins remain uncertain. Present a spectroscopic study of eight such stars, based on new Gemini GNIRS and NIFS NIR observations. This work has led to the discovery of a new O If+ star. Compare the reddening-corrected J-K vs K diagram for the stars with the massive ones in the Arches cluster and use stellar evolutionary tracks to constrain their ages and masses. The radial velocities of both the stars and their nearby H II regions are also reported. All of the stars are blue shifted relative to the Arches cluster by > 50 km/s. Find that the source P35 has a velocity consistent with that of the surrounding molecular gas. The velocity gradient of nearby ionized gas along the Gemini GNIRS long slit, relative to P35 and the adjacent -30-0 km/s molecular cloud, can best be explained by a pressure-driven flow model. Thus, P35 most likely formed in situ. 3 more of the stars have radial velocities different from their adjacent molecular gas, indicating that they are interlopers. The 4 stars closest to the Arches cluster have similar spectra, ages and masses to known cluster members, suggesting that they were likely ejected from the cluster via 3-body interactions. Therefore, find that the relatively isolated stars partly formed in situ and partly were ejected from the known star clusters in the Galactic Center.
1410.2898
MC^2: Constraining the dark matter distribution of the violent merging galaxy cluster CIZA J2242.8+5301 by piercing through the Milky Way
Jee, ... Wittman, Hoekstra, ... et al
A merging system with a prominent (~2 Mpc long) radio relic, which together with the morphology of the X-ray emission provides strong evidence for a violent collision along the N-S axis. Present constraints on the DM distribution of this unusual system using Subaru and CFHT imaging data. Measuring a high S/N lensing signal from this cluster is potentially a challenging task because of its proximity to the MW plane (|b|~5 deg). Overcome this challenge with careful observation planning and systematics control, which enables mapping the DM distribution of the cluster with high fidelity. The resulting mass map shows that the mass distribution is highly elongated along the N-S merger axis inferred from the orientation of the radio relics. Based on the mass reconstruction, identify 2 sub-clusters, which coincide with the cluster galaxy distributions. Determine their masses using MCMC analysis by fitting 2 NFW haloes without fixing their centroids. M200=11e14 Msun and 9.8e14 Msun, respectively, indicating a post-collision of 2 giant systems of nearly equal mass. When the mass and galaxy centroids are compared in detail, detect ~1' (~190 kpc) offsets in both N and S sub-clusters. Find that the galaxy luminosity-mass offset for the N clump is statistically signifiant at the 2 sigma level, whereas the detection is only marginal for the S sub-cluster in part because of a relatively large mass centroid error. Conclude that it is yet premature to uniquely attribute the galaxy-mass misalignment to SIDM and discuss caveats.
1410.3266
Prospect for UV observations from the Moon
Safonova et al
Indian entry to the Google Lunar X PRIZE competition, "Team Indus" mission, expected to deliver ~30 kg of payloads to the Moon, with a rover as its primary payload. Propose to mount a wide-field FUV (130-180 nm) imaging telescope as a payload on the Team Indus lander. Fixed zenith pointing but with the option of a mechanism to allow observations of different attitudes. Pointing towards intermediate ecliptic latitude (50 deg or above) ensures that the Sun is at least 40 deg off the line of sight at all times. In this position, the telescope can cover higher galactic latitudes as well as parts of Galactic plane.
1410.3282
How well can cold-dark-matter substructures account for the observed radio flux-ratio anomalies?
Xu, Sluse, Gao, Wang, Frenk, Mao, Schneider, Springel
Construct samples of generalized and specific lens potentials, to which add (rescaled) sub halo populations from the galaxy-scale Aquarius and the cluster-scale Phoenix simulation suites. Further investigate the lensing effects from sub haloes of masses several orders of magnitude below the simulation resolution limit. The resulting flux ratio distributions are compared to the currently best available sample of radio lenses. The observed anomalies in 3 specific samples are more likely to be caused by propagation effects or oversimplified lens modeling, singes of which are already seen in the data. Among the quadruple systems that have closely located image triplets/pairs, the anomalous flux ratios of MG0414+0534 can be reproduced by adding CDM sub haloes to its macroscopic lens potential, with a probability of 5-20%, for the 4 systems, these probabilities are only a few percent. Hence find that CDM substructures are unlikely to be the whole reason for radio flux anomalies. Discuss other possible effects that might also be at work.
1410.2768
Origins of massive field stars in the galactic center: a spectroscopic study
Dong et al
A large number of evolved massive stars have been detected in the Galactic Center, outside the known star clusters; but their origins remain uncertain. Present a spectroscopic study of eight such stars, based on new Gemini GNIRS and NIFS NIR observations. This work has led to the discovery of a new O If+ star. Compare the reddening-corrected J-K vs K diagram for the stars with the massive ones in the Arches cluster and use stellar evolutionary tracks to constrain their ages and masses. The radial velocities of both the stars and their nearby H II regions are also reported. All of the stars are blue shifted relative to the Arches cluster by > 50 km/s. Find that the source P35 has a velocity consistent with that of the surrounding molecular gas. The velocity gradient of nearby ionized gas along the Gemini GNIRS long slit, relative to P35 and the adjacent -30-0 km/s molecular cloud, can best be explained by a pressure-driven flow model. Thus, P35 most likely formed in situ. 3 more of the stars have radial velocities different from their adjacent molecular gas, indicating that they are interlopers. The 4 stars closest to the Arches cluster have similar spectra, ages and masses to known cluster members, suggesting that they were likely ejected from the cluster via 3-body interactions. Therefore, find that the relatively isolated stars partly formed in situ and partly were ejected from the known star clusters in the Galactic Center.
1410.2898
MC^2: Constraining the dark matter distribution of the violent merging galaxy cluster CIZA J2242.8+5301 by piercing through the Milky Way
Jee, ... Wittman, Hoekstra, ... et al
A merging system with a prominent (~2 Mpc long) radio relic, which together with the morphology of the X-ray emission provides strong evidence for a violent collision along the N-S axis. Present constraints on the DM distribution of this unusual system using Subaru and CFHT imaging data. Measuring a high S/N lensing signal from this cluster is potentially a challenging task because of its proximity to the MW plane (|b|~5 deg). Overcome this challenge with careful observation planning and systematics control, which enables mapping the DM distribution of the cluster with high fidelity. The resulting mass map shows that the mass distribution is highly elongated along the N-S merger axis inferred from the orientation of the radio relics. Based on the mass reconstruction, identify 2 sub-clusters, which coincide with the cluster galaxy distributions. Determine their masses using MCMC analysis by fitting 2 NFW haloes without fixing their centroids. M200=11e14 Msun and 9.8e14 Msun, respectively, indicating a post-collision of 2 giant systems of nearly equal mass. When the mass and galaxy centroids are compared in detail, detect ~1' (~190 kpc) offsets in both N and S sub-clusters. Find that the galaxy luminosity-mass offset for the N clump is statistically signifiant at the 2 sigma level, whereas the detection is only marginal for the S sub-cluster in part because of a relatively large mass centroid error. Conclude that it is yet premature to uniquely attribute the galaxy-mass misalignment to SIDM and discuss caveats.
1410.3266
Prospect for UV observations from the Moon
Safonova et al
Indian entry to the Google Lunar X PRIZE competition, "Team Indus" mission, expected to deliver ~30 kg of payloads to the Moon, with a rover as its primary payload. Propose to mount a wide-field FUV (130-180 nm) imaging telescope as a payload on the Team Indus lander. Fixed zenith pointing but with the option of a mechanism to allow observations of different attitudes. Pointing towards intermediate ecliptic latitude (50 deg or above) ensures that the Sun is at least 40 deg off the line of sight at all times. In this position, the telescope can cover higher galactic latitudes as well as parts of Galactic plane.
1410.3282
How well can cold-dark-matter substructures account for the observed radio flux-ratio anomalies?
Xu, Sluse, Gao, Wang, Frenk, Mao, Schneider, Springel
Construct samples of generalized and specific lens potentials, to which add (rescaled) sub halo populations from the galaxy-scale Aquarius and the cluster-scale Phoenix simulation suites. Further investigate the lensing effects from sub haloes of masses several orders of magnitude below the simulation resolution limit. The resulting flux ratio distributions are compared to the currently best available sample of radio lenses. The observed anomalies in 3 specific samples are more likely to be caused by propagation effects or oversimplified lens modeling, singes of which are already seen in the data. Among the quadruple systems that have closely located image triplets/pairs, the anomalous flux ratios of MG0414+0534 can be reproduced by adding CDM sub haloes to its macroscopic lens potential, with a probability of 5-20%, for the 4 systems, these probabilities are only a few percent. Hence find that CDM substructures are unlikely to be the whole reason for radio flux anomalies. Discuss other possible effects that might also be at work.
Day 762
Monday.
1410.2238
Radial migration of the Sun in the Milky Way: A Statistical study
MartÃnez-Barbosa, Brown, Portegies-Zwart
Find that in general it is unlikely that the Sun has migrated significantly from the inner regions of the Galactic disk to R_\odot.
1410.2244
The stellar accretion origin of stellar population gradients in massive galaxies at large radii
Hirschmann et al
Use 10 cosmological zoom sims of haloes with 6e12 Msun < Mhalo < 2e13 Msun. The simulations follow metal cooling and enrichment from SNII, SNIa and AGB winds. Explore the differential impact of an empirical model for galactic winds that reproduces the mass-metallicity relation and its evolution with redshift. At larger radii the galaxies, for both models, become more dominated by stars accreted from satellite galaxies in major and minor mergers. In the wind model, fewer stars are accreted, but they are significantly more metal poor resulting in steep global metallicity and color. In contrast, color and metallicity gradients of the models without winds are inconsistent with observations. Age gradients are in general mildly positive at z=0 with significant differences between the models at higher redshift. Demonstrate that for the wind model, stellar accretion is steepening existing in-situ metallicity gradients by about 0.2 dex by the present day and helps to match observed gradients of massive early-type galaxies at large radii. Color and metallicity gradients are significantly steeper for systems which have accreted stars in minor mergers, while galaxies with major mergers have relatively flat gradients, confirming previous results. This study highlights the importance of stellar accretion for stellar population properties of massive galaxies at large radii, which can provide important constraints for formation models.
1410.2250
A new probe of magnetic fields in the pre-reinization epoch: I. formalism
Venumadhav, ... Hirata, etal
Propose a method of measuring extremely weak B-fields in the inter galactic medium prior to and during the epoch of cosmic reionization. The method utilizes the Larmor precession of spin-polarized neutral hydrogen in the triplet state of the hyperfine transition. The resulting change in the brightness temperature fluctuations encodes information about the B-field the atoms are immersed in. The method is most suited to probing fields that are coherent on large scales. Due to the long lifetime of the triplet state of the 21-cm transition, this technique is naturally sensitive to extremely weak field strengths, of order 1e-19 G (or 1e-21 G if scaled to the present day). Therefore, this might open up the possibility of probing primordial B-fields just prior to reionization. Moreover, such measurements are unaffected by later B-fields since 21-cm observations preserve redshift information. If the B-fields are much stronger, it is still possible to recover information about their orientation. In this paper, perform detailed calculations of the microphysics behind this effect, and take into account all the processes that affect the hyperfine transition, including radiative decays, collisions, and optical pumping by Lyman-alpha photons. Conclude with an analytic formula for the brightness temperature of linear-regime fluctuations in the presence of a B-feld, and discuss its limiting behavior for weak and strong fields.
1410.2276
The next generation Virgo cluster survey. XV. The photometric redshift estimation for background sources
Raichoor, Mei, Erben, Hildebrandt, ... Ilbert, et al
The NGVCS is an optical imaging survey covering 104 sq deg centered on the Virgo cluster. The complete survey area has been observed in the u*giz-bands and one third in the r-band. Present the photometric z estimation fro the NGVS background sources. After a dedicated data reduction, perform accurate photometry, with special attention to precise color measurements through PSF homogenization. Then estimate the photometric z with the LePhare and BPZ codes. Add a new prior which extends to iAB=12.5 mag. Using the u*giz-bands, photometric redshifts for 15.5 <= i <~ 23 mag or zphot <~1 galaxies have bias |Delta z|<0.02, less than 5% outliers, and a scatter sigma_outl.reg. and an individual error on zphot that increase with magnitude (from 0.02 to 0.05 and from 0.03 to 0.10, respectively). When using the u*giz-bands over the same magnitude and redshift range, the lack of the r-band increases the uncertainties in the 0.3 ~ zphot <~0.8 range. Also present a joint analysis of the photo-z accuracy as a function of z and magnitude. Assess the quality of the photometric z by comparison to spectroscopic sample across z bins is in agreement with the expectations.
1410.2341
The size evolution of elliptical galaxies
Zie, Guo, Cooper, Frenk, Li, Gao
Possibility of the amplitude of the size mass relation of massive early type galaxies evolves with z. Use SAM to study the size evolution of massive ETGs; find this model is able to reproduce the amplitude of present day amplitude and slope of the relation between size and stellar mass for these galaxies, as well as its evolution. The amplitude of this relation reflects the typical compactness of dark halos at the time when most of the stars are formed. This link between size and SF epoch is propagated in galaxy mergers. Mergers of high or moderate mass ratio (<1:3) become increasingly important with increasing present day stellar mass for galaxies more massive than 1e11.4 Msun. At lower masses, low mass ratio mergers play a more important role. In situ SF contribute more to the size growth than it does to stellar mass growth. Also find that, for ETGs identified at z=2, minor mergers dominate subsequent growth both for stellar mass and in size, consistent with earlier theoretical results.
1410.2533
Gravitational lensing of cosmological 21cm emission
Pourtsidou, Metcalf
Investigate the feasibility of measuring WL using 21cm intensity mapping with emphasis on the performance of the planned SKA. Find that the current design for SKA-Mid should be able to measure the evolution of the lensing PS at z~2-3 using this technique. This will be a probe of the expansion history of the universe and gravity at a unique range in redshift. The S/N is found to be highly dependent on evolution of the neutral H fraction in the universe with a higher HI density resulting in stronger signal. With realistic models for this , SKA Phase 1 should be capable of measuring the lensing PS and its evolution. The S/N dependence on the area and diameter of the telescope array is quantified. Further demonstrate the applications of this technique by applying it to two specific coupled DE models that would be difficult to observationally distinguish without information from this range of z. Also investigate measuring the lensing signal with 21cm emission from the EoR using SKA-Low and find that it is unlikely to constrain cosmo parameters because of the small survey size, but could provide a map of the DM within a small region of the sky.
1410.2238
Radial migration of the Sun in the Milky Way: A Statistical study
MartÃnez-Barbosa, Brown, Portegies-Zwart
Find that in general it is unlikely that the Sun has migrated significantly from the inner regions of the Galactic disk to R_\odot.
1410.2244
The stellar accretion origin of stellar population gradients in massive galaxies at large radii
Hirschmann et al
Use 10 cosmological zoom sims of haloes with 6e12 Msun < Mhalo < 2e13 Msun. The simulations follow metal cooling and enrichment from SNII, SNIa and AGB winds. Explore the differential impact of an empirical model for galactic winds that reproduces the mass-metallicity relation and its evolution with redshift. At larger radii the galaxies, for both models, become more dominated by stars accreted from satellite galaxies in major and minor mergers. In the wind model, fewer stars are accreted, but they are significantly more metal poor resulting in steep global metallicity and color. In contrast, color and metallicity gradients of the models without winds are inconsistent with observations. Age gradients are in general mildly positive at z=0 with significant differences between the models at higher redshift. Demonstrate that for the wind model, stellar accretion is steepening existing in-situ metallicity gradients by about 0.2 dex by the present day and helps to match observed gradients of massive early-type galaxies at large radii. Color and metallicity gradients are significantly steeper for systems which have accreted stars in minor mergers, while galaxies with major mergers have relatively flat gradients, confirming previous results. This study highlights the importance of stellar accretion for stellar population properties of massive galaxies at large radii, which can provide important constraints for formation models.
1410.2250
A new probe of magnetic fields in the pre-reinization epoch: I. formalism
Venumadhav, ... Hirata, etal
Propose a method of measuring extremely weak B-fields in the inter galactic medium prior to and during the epoch of cosmic reionization. The method utilizes the Larmor precession of spin-polarized neutral hydrogen in the triplet state of the hyperfine transition. The resulting change in the brightness temperature fluctuations encodes information about the B-field the atoms are immersed in. The method is most suited to probing fields that are coherent on large scales. Due to the long lifetime of the triplet state of the 21-cm transition, this technique is naturally sensitive to extremely weak field strengths, of order 1e-19 G (or 1e-21 G if scaled to the present day). Therefore, this might open up the possibility of probing primordial B-fields just prior to reionization. Moreover, such measurements are unaffected by later B-fields since 21-cm observations preserve redshift information. If the B-fields are much stronger, it is still possible to recover information about their orientation. In this paper, perform detailed calculations of the microphysics behind this effect, and take into account all the processes that affect the hyperfine transition, including radiative decays, collisions, and optical pumping by Lyman-alpha photons. Conclude with an analytic formula for the brightness temperature of linear-regime fluctuations in the presence of a B-feld, and discuss its limiting behavior for weak and strong fields.
1410.2276
The next generation Virgo cluster survey. XV. The photometric redshift estimation for background sources
Raichoor, Mei, Erben, Hildebrandt, ... Ilbert, et al
The NGVCS is an optical imaging survey covering 104 sq deg centered on the Virgo cluster. The complete survey area has been observed in the u*giz-bands and one third in the r-band. Present the photometric z estimation fro the NGVS background sources. After a dedicated data reduction, perform accurate photometry, with special attention to precise color measurements through PSF homogenization. Then estimate the photometric z with the LePhare and BPZ codes. Add a new prior which extends to iAB=12.5 mag. Using the u*giz-bands, photometric redshifts for 15.5 <= i <~ 23 mag or zphot <~1 galaxies have bias |Delta z|<0.02, less than 5% outliers, and a scatter sigma_outl.reg. and an individual error on zphot that increase with magnitude (from 0.02 to 0.05 and from 0.03 to 0.10, respectively). When using the u*giz-bands over the same magnitude and redshift range, the lack of the r-band increases the uncertainties in the 0.3 ~ zphot <~0.8 range. Also present a joint analysis of the photo-z accuracy as a function of z and magnitude. Assess the quality of the photometric z by comparison to spectroscopic sample across z bins is in agreement with the expectations.
1410.2341
The size evolution of elliptical galaxies
Zie, Guo, Cooper, Frenk, Li, Gao
Possibility of the amplitude of the size mass relation of massive early type galaxies evolves with z. Use SAM to study the size evolution of massive ETGs; find this model is able to reproduce the amplitude of present day amplitude and slope of the relation between size and stellar mass for these galaxies, as well as its evolution. The amplitude of this relation reflects the typical compactness of dark halos at the time when most of the stars are formed. This link between size and SF epoch is propagated in galaxy mergers. Mergers of high or moderate mass ratio (<1:3) become increasingly important with increasing present day stellar mass for galaxies more massive than 1e11.4 Msun. At lower masses, low mass ratio mergers play a more important role. In situ SF contribute more to the size growth than it does to stellar mass growth. Also find that, for ETGs identified at z=2, minor mergers dominate subsequent growth both for stellar mass and in size, consistent with earlier theoretical results.
1410.2533
Gravitational lensing of cosmological 21cm emission
Pourtsidou, Metcalf
Investigate the feasibility of measuring WL using 21cm intensity mapping with emphasis on the performance of the planned SKA. Find that the current design for SKA-Mid should be able to measure the evolution of the lensing PS at z~2-3 using this technique. This will be a probe of the expansion history of the universe and gravity at a unique range in redshift. The S/N is found to be highly dependent on evolution of the neutral H fraction in the universe with a higher HI density resulting in stronger signal. With realistic models for this , SKA Phase 1 should be capable of measuring the lensing PS and its evolution. The S/N dependence on the area and diameter of the telescope array is quantified. Further demonstrate the applications of this technique by applying it to two specific coupled DE models that would be difficult to observationally distinguish without information from this range of z. Also investigate measuring the lensing signal with 21cm emission from the EoR using SKA-Low and find that it is unlikely to constrain cosmo parameters because of the small survey size, but could provide a map of the DM within a small region of the sky.
Sunday, October 12, 2014
Day 761
Thursday. Friday.
Nature
An ultraluminous X-ray source powered by an accreting neutron star
The majority of UL X-ray sources are point sources that are spatially offset from the nuclei of nearby galaxies and whose X-ray luminosities exceed the theoretical maximum for spherical infall (the Eddington limit) onto stellar-mass BHs. Their X-ray L in the 0.5-10 keV energy range from 1e39 to 41 ergs/s. Because higher masses imply less extreme ratios of the luminosity to the isotropic Eddington limit, theoretical models have focused on the BH rather than neutron star systems. The most challenging sources to explain are those at the luminous end of the range (more than 1e40 ergs/s), which require BH masses of 50-100 times the solar value or significant departures from the standard thin disk accretion that powers bright galactic X-ray binaries, or both. Here report broadband X-ray observations of the nuclear region of the galaxy M82 that reveal pulsations with an average period of 1.37 S and a 2.5 day sinusoidal modulation. The pulsations results from the rotation of a magnetized NS, and the modulation arises from its binary orbit. The pulsed flux alone corresponds to an X-ray luminosity in the 3-30 keV range of 4.9e39 ergs/s. The pulsating sources is spatially coincident with a variable source that can reach an X-ray luminosity in the 0.3-10 keV range of 1.8e40 ergs/s. This association implies a luminosity of about 100 x the Eddington limit for a 1.4 Msun object, or more than 10x brighter than any known accreting pulsar. This implies that NSs may not be rare in the UL X-ray population, and it challenges physical models for the accretion of matter onto magnetized compact objects.
1410.1874
Neutrino viscosity and drag: impact on the magnetorotational instability in proto-neutron stars
Guilet, Mueller, Janka
The magneto-rotational instability (MRI) is a promising mechanism to amplify the B-field in fast rotation proto-NSs (PNS). The diffusion of neutrinos trapped in the PNS induces a transport of momentum, which can be modeled as a viscosity on length scales longer than the neutrino mean free path. This neutrino-viscosity can slow down the growth of MRI modes to such an extent that a minimum initial B-field strength of >1e12 G is needed for the MRI to grow on a sufficiently short timescale to potentially affect the explosion. It is uncertain whether the B-field of fast rotating progenitor cores is strong enough to yield such an initial B-field in PNSs. At MRI wavelengths shorter than the neutrino mean free path, on the other hand, neutrino radiation does not act as a viscosity but rather induces a drag on the velocity with a damping rate independent of the wavelength. Perform a linear analysis of the MRI in this regime, and apply the analytical results to the proto-NS structure from a one-dimensional numerical simulation. Show that in the outer layers of the PNS, the MIR can grow from weak B-fields at wavelengths shorter than the neutrino mean free path, while deeper in the PNS MRI growth takes place in the viscous regime and requires a minimum B-field strength.
1410.1893
Origin of magnetic field in the intracluster medium: primordial or astrophysical?
Cho
The origin of B-fields in clusters of galaxies is still and unsolved problem, which is largely due to the poor understanding of initial seed B-fields. If the seed magnetic fields have primordial origins, it is likely that large-scale pervasive B-fields were present before the formation of the large-scale structure. On the other hand, if they were ejected from astrophysical bodies, they were highly localized in space at the time of injection. In this paper, using turbulence dynamo models for high magnetic Prandtl number fluids, find constraints on the seed B-fields. The hydrodynamic Reynolds number based on the Spitzer viscosity in the ICM is believed to be less than O(1e2), while the magnetic Reynolds number can be much larger than that. IN this case, if the seed magnetic fields have primordial origins, they should be stronger than O(1e-11) G, which is very close to the upper limit of O(1e-9)G set by the CMB observations. On the other hand, if the seed B-fields were ejected from astrophysical bodies, any seed B-fields stronger than O(1e-9) G can safely magnetize the ICM. Therefore, it is less likely that primordial B-fields are the direct origin of present-day B-fields in the ICM.
Nature
An ultraluminous X-ray source powered by an accreting neutron star
The majority of UL X-ray sources are point sources that are spatially offset from the nuclei of nearby galaxies and whose X-ray luminosities exceed the theoretical maximum for spherical infall (the Eddington limit) onto stellar-mass BHs. Their X-ray L in the 0.5-10 keV energy range from 1e39 to 41 ergs/s. Because higher masses imply less extreme ratios of the luminosity to the isotropic Eddington limit, theoretical models have focused on the BH rather than neutron star systems. The most challenging sources to explain are those at the luminous end of the range (more than 1e40 ergs/s), which require BH masses of 50-100 times the solar value or significant departures from the standard thin disk accretion that powers bright galactic X-ray binaries, or both. Here report broadband X-ray observations of the nuclear region of the galaxy M82 that reveal pulsations with an average period of 1.37 S and a 2.5 day sinusoidal modulation. The pulsations results from the rotation of a magnetized NS, and the modulation arises from its binary orbit. The pulsed flux alone corresponds to an X-ray luminosity in the 3-30 keV range of 4.9e39 ergs/s. The pulsating sources is spatially coincident with a variable source that can reach an X-ray luminosity in the 0.3-10 keV range of 1.8e40 ergs/s. This association implies a luminosity of about 100 x the Eddington limit for a 1.4 Msun object, or more than 10x brighter than any known accreting pulsar. This implies that NSs may not be rare in the UL X-ray population, and it challenges physical models for the accretion of matter onto magnetized compact objects.
1410.1874
Neutrino viscosity and drag: impact on the magnetorotational instability in proto-neutron stars
Guilet, Mueller, Janka
The magneto-rotational instability (MRI) is a promising mechanism to amplify the B-field in fast rotation proto-NSs (PNS). The diffusion of neutrinos trapped in the PNS induces a transport of momentum, which can be modeled as a viscosity on length scales longer than the neutrino mean free path. This neutrino-viscosity can slow down the growth of MRI modes to such an extent that a minimum initial B-field strength of >1e12 G is needed for the MRI to grow on a sufficiently short timescale to potentially affect the explosion. It is uncertain whether the B-field of fast rotating progenitor cores is strong enough to yield such an initial B-field in PNSs. At MRI wavelengths shorter than the neutrino mean free path, on the other hand, neutrino radiation does not act as a viscosity but rather induces a drag on the velocity with a damping rate independent of the wavelength. Perform a linear analysis of the MRI in this regime, and apply the analytical results to the proto-NS structure from a one-dimensional numerical simulation. Show that in the outer layers of the PNS, the MIR can grow from weak B-fields at wavelengths shorter than the neutrino mean free path, while deeper in the PNS MRI growth takes place in the viscous regime and requires a minimum B-field strength.
1410.1893
Origin of magnetic field in the intracluster medium: primordial or astrophysical?
Cho
The origin of B-fields in clusters of galaxies is still and unsolved problem, which is largely due to the poor understanding of initial seed B-fields. If the seed magnetic fields have primordial origins, it is likely that large-scale pervasive B-fields were present before the formation of the large-scale structure. On the other hand, if they were ejected from astrophysical bodies, they were highly localized in space at the time of injection. In this paper, using turbulence dynamo models for high magnetic Prandtl number fluids, find constraints on the seed B-fields. The hydrodynamic Reynolds number based on the Spitzer viscosity in the ICM is believed to be less than O(1e2), while the magnetic Reynolds number can be much larger than that. IN this case, if the seed magnetic fields have primordial origins, they should be stronger than O(1e-11) G, which is very close to the upper limit of O(1e-9)G set by the CMB observations. On the other hand, if the seed B-fields were ejected from astrophysical bodies, any seed B-fields stronger than O(1e-9) G can safely magnetize the ICM. Therefore, it is less likely that primordial B-fields are the direct origin of present-day B-fields in the ICM.
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