Tuesday.
1511.08804
The stellar mass assembly of galaxies in the Illustris simulation: growth by mergers and the spatial distribution of accreted stars
Rodriguez-Gomez, et al
Use Illustris sim to study the relative contributions of in situ SF and stellar accretion to the buildup of galaxies over an unprecedentedly wide range of masses (M*=1e9-12 Msun), galaxies types, environments, and assembly histories. Find that the 'two-phase' picture of galaxy formation predicted by some models is a good approximation only for the most massive galaxies in the sim -- namely, the stellar mass growth of galaxies below a few times 1e11 Msun is dominated by in situ SF at all redshifts, while galaxies above this mass at z<1 grow primarily by accretion of stars via mergers. The fraction of the total stellar mass of galaxies at z=0 contributed by accreted stars shows a strong dependence on galaxy stellar mass, ranging from about 10% for MW-sized galaxies to over 80% for M*~1e12 Msun objects, yet with a large galaxy-to-galaxy variation. At a fixed stellar mass, elliptical galaxies and those formed at the centers of younger haloes exhibit larger fractions of ex situ stars than disc-like galaxies and those formed in older haloes. On average, ~50% of the ex situ stellar mass comes from major mergers (stellar mass ratio mu > 1/4), ~20% from minor mergers (1/10<mu<1/4), ~20% from very minor mergers (mu<1/10), and ~10% from stars that were stripped from surviving galaxies (e.g. flybys or ongoing mergers). These components are spatially segregated, with in situ stars dominated the innermost regions of galaxies, and ex situ stars being deposited at larger galactocentric distances in order of decreasing merger mass ratio. The 'transition' radius where ex situ stars begin to dominated over the in situ class decreases fro more massive galaxies and correlated strongly with the total ex situ fraction.
1511.08809
Isolated elliptical galaxies in the local Universe
Lacerna, et al
Study a sample of 89 very isolated elliptical galaxies at z<0.08 and compared their properties with elliptical galaxies located in a high-density environment such as the Coma supercluster. The aim is to probe the role of environment on the morphological transformation and quenching of elliptical galaxies as a function of mass. In addition, elucidate about the nature of a particular set of blue and SF isolated ellipticals identified here. Study physical properties of ellipticals scubas color, sSFR, galaxy size and stellar age as a function of stellar mass and environment based on SDSS data. Analyze in more detail the blue SF isolated ellipticals through photometric characterization using GALFIT and infer their SFH using STARLIGHT. Among the isolated ellipticals ~20% are blue, 8% are star-forming and ~10% are recently quenched, while among the Coma ellipticals, ~8% are blue and just <=1% are star-forming or recently quenched. There are four isolated galaxies (~4.5%) that are blue and SF at the same time. These galaxies, with masses between 7e9 and 2e10 Msun/h^2, are also the youngest galaxies with light-weighted stellar ages <= 1Gyr and exhibit bluer colors toward the galaxy center. Around 30-60% of their present-day luminosity, but only <5% of their present-day mass, is due to SF in the last 1 Gyr. The processes of morphological transformation and quenching seem to be in general independent of environment since most of elliptical galaxies are "red and dead", although the transition to the red sequence should be faster for isolated ellipticals [why?]. In some cases, the isolated environment seems to propitiate the rejuvenation of ellipticals by recent (<1 Gyr) cold gas accretion.
1511.09008
Cosmic troublemakers: the Cold Spot, the Eridanus Supervoid, and the Great Walls
Kovács, García-Bellido
The alignment of the CMB Cold Spot and the Eridanus Supervoid suggests a physical connection between these two relatively rare objects. Use galaxy catalogues with photometric (2MPZ) and spectroscopic (6dF) redshift measurements, supplemented by low-redshift compilations of cosmic voids, in order to improve the 3D mapping of the matter density in the Eridanus constellation. Find evidence for a super void with an important elongation in the LoS, effectively spanning the total redshift range z<0.3. The tomographic imaging reveals significant substructure in the Eridanus Supervoid, with a potential interpretation of a long, fully connected system of voids. Improve the analysis by extending the LoS measurements into the antipodal direction, that interestingly crosses the Northern Local Supervoid at the lowest redshifts, and intersects very rich superclusters like Hercules and Corona Borealis, in the region of the Coma and Sloan Great Walls, as a possible compensation for the large-scale matter deficit of Eridanus. Model the matter density profiles with ellipsoidal super voids, and find that large-scale structure measurements are consistent with a central matter under density delta0~-0.25, with transverse radius r0\perp~55 Mpc/h and LoS radius r0\parallel~440 Mpc/h. Based on these findings, propose a potential explanation for the Cold Spot in the CMB, and for the hot ring feature around it, as a combination of a positive primordial fluctuation and an extremely cold ISW imprint.
1511.09132
Clustering properties and halo masses for central galaxies in the local Universe
Wang, Li, Jing
Investigate the clustering and DM halo mass for a sample of ~16k central galaxies selected from SDSS/DR7 group catalog. Select subsamples of central galaxies on three 2-D planes, each formed by stellar mass (M*) and one of the other properties including optical color (g-r), surface stellar mass density (mu*), and central stellar velocity dispersion (sigma*). For each subsample, measure both the projected cross-correlation function (wp(rp)) relative to a reference galaxy sample, and an average mass of the host DM haloes (Mhalo). For comparison also estimate the wp(rp) for the full galaxy population and the subset of satellite galaxies. Find that, for central galaxies, both wp(rp) and Mhalo show strongest dependence on M*, and there is no clear dependence on other properties when stellar mass is fixed. This result provides strong support to the previously-adopted assumption that, for central galaxies, stellar mass is the galaxy property that is best indicative of the host halo mass. The full galaxy population and the subset of satellites show similar clustering properties in all cases. However, they are similar to the centrals only at high masses (M*>1e11 Msun). At low-mass (M*<1e11 Msun), the results are different: the wp(rp) increases with both sigma and g-r when M* is fixed, and depends very weakly on M* when sigma* or g-r is fixed. At fixed Mstar, the mu* shows weak correlations with clustering amplitude (and halo mass for central galaxies). The results suggest that it is necessary to consider central and satellite galaxies separately when studying the link between galaxies and DM haloes.
Monday, November 30, 2015
Sunday, November 29, 2015
Day 1013
Monday after Thanksgiving.
1511.08211
MultiDarkLens Simulations: weak lensing light-cones and data base presentation
Giocoli, Jullo, Metcalf, et al
Present a large database of WL light cones constructed using different snapshots of the Big MultiDark sim (BigMDPL). The ray-tracing through different multiple planes has been performed with the GLAMER code accounting both for single source redshifts and for sources distributed along the cosmic time. This first paper presents WL forecasts and results according to the geometry of the VIPERS-W1and W4 field of view. Additional fields will be available on the database and new ones can be run upon request. The database also contains some tools for lensing analysis. In this paper, present results for convergence power spectra, one point and high order WL statistics useful for forecasts and for cosmo studies. Covariance matrices have also been computed for the different realizations of the W1 and W4 fields. In addition compute also galaxy-shear and projected density contrasts for different halo masses at two lens redshifts according to the CFHTLS source redshift distribution both using stacking and cross-correlation techniques, finding very good agreement.
1511.08212
The lifecycle of clusters in galaxies
Adamo, Bastian
Review basic properties of star cluster systems, and how they relate to their host galaxy properties and ambient environment. Custer mass and LFs well approximated by power laws with alpha~-2 over most of the observable range. Both become steeper at high masses/luminosities, with the value of the downward turn dependent on environment. The host galaxy properties also appear to affect the cluster formation efficiency (Gamma - i.e., the fraction of stars that form in bound clusters), with higher star-formation rate density galaxies having higher Gamma values. Within individual galaxies, there is evidence for Gamma to vary by a factor of 3-4, likely following the molecular gas surface density, in agreement with recent predictions. Finally, discuss cluster disruption and its effect on the observed properties of a population, focussing on the age distribution of clusters. Briefly discuss the expectations of theoretical and numerical studies, and also the observed distributions in a number of galaxies. Most observational studies now find agreement with theoretical expectations, namely nearly a constant cluster age distribution for ages up to ~100 Myr (i.e., little disruption), and a drastic steepening above this value caused by a combination of cluster disruption and incompleteness. Rapid cluster disruption for clusters with ages <100 Myr is ruled out for most galaxies.
1511.08311
The Megamaser Cosmology project VIII. A geometric distance to NGC 5765b
Gao, et al
Present a new geometric distance measurement to the megamaser galaxy NGC 5765b. Confirmed the water masers trace a thin, sub parsec Keplerian disk around the nucleus, implying an enclosed mass of 4.55±0.40e7 Msun. Meanwhile, from observations over 2 years, measure the secular drifts of maser features near the systemic velocity of the galaxy with rates between 0.5 and 1.2 km/s/yr. Fitting a warped, thin disk model to these measurements, determine a Hubble constant H0 of 66.0±6.0 km/s/Mpc with the angular-diameter distance to 126.3±11.6 Mpc. Apart from the distance measurement, also investigate some physical properties related to the maser disk in the galaxy. The high-velocity features are spatially distributed into several clumps, which may indicate the existence of a spiral density wave associated with the accretion disk. For the red-shifted features, the envelope defined by the peak maser intensities increases with radius. The profile of the systemic masers in the galaxy is smooth and shows almost no structural changes over the 2 years of monitoring time, which differs form the more variable case of NGC 4258.
1511.08502
How big can a black hole grow?
King
Show that there is a physical limit to the mass of a BH, above which it cannot grow through luminous accretion of gas, and so cannot appear as a quasar or AGN. The limit is M_max~5e10 Msun for typically parameters, but can reach 2.7e11 Msun in extreme cases (maximal prograde spin). The largest BH masses so far found are close but below the limit. The Eddington luminosity ~ 6.5e48 erg/s corresponding to Mmax is remarkable close to the largest AGN bolometric luminosity so far observed. The mass and luminosity limits both rely on a reasonable but currently untestable hypothesis about AGN disk formation, so future observations of extreme SMBH masses can therefore probe fundamental disc physics. BHs can in principle glow their masses above Mmax by non-luminous means such as mergers with other holes, but cannot become luminous accretions again. They might nevertheless be detectable in other ways, for example through gravitational lensing. Show further that BHs with masses~Mmax can probably grow above the values specified by the BH -- host-galaxy scaling relations, in a agreement with observation.
1511.08211
MultiDarkLens Simulations: weak lensing light-cones and data base presentation
Giocoli, Jullo, Metcalf, et al
Present a large database of WL light cones constructed using different snapshots of the Big MultiDark sim (BigMDPL). The ray-tracing through different multiple planes has been performed with the GLAMER code accounting both for single source redshifts and for sources distributed along the cosmic time. This first paper presents WL forecasts and results according to the geometry of the VIPERS-W1and W4 field of view. Additional fields will be available on the database and new ones can be run upon request. The database also contains some tools for lensing analysis. In this paper, present results for convergence power spectra, one point and high order WL statistics useful for forecasts and for cosmo studies. Covariance matrices have also been computed for the different realizations of the W1 and W4 fields. In addition compute also galaxy-shear and projected density contrasts for different halo masses at two lens redshifts according to the CFHTLS source redshift distribution both using stacking and cross-correlation techniques, finding very good agreement.
1511.08212
The lifecycle of clusters in galaxies
Adamo, Bastian
Review basic properties of star cluster systems, and how they relate to their host galaxy properties and ambient environment. Custer mass and LFs well approximated by power laws with alpha~-2 over most of the observable range. Both become steeper at high masses/luminosities, with the value of the downward turn dependent on environment. The host galaxy properties also appear to affect the cluster formation efficiency (Gamma - i.e., the fraction of stars that form in bound clusters), with higher star-formation rate density galaxies having higher Gamma values. Within individual galaxies, there is evidence for Gamma to vary by a factor of 3-4, likely following the molecular gas surface density, in agreement with recent predictions. Finally, discuss cluster disruption and its effect on the observed properties of a population, focussing on the age distribution of clusters. Briefly discuss the expectations of theoretical and numerical studies, and also the observed distributions in a number of galaxies. Most observational studies now find agreement with theoretical expectations, namely nearly a constant cluster age distribution for ages up to ~100 Myr (i.e., little disruption), and a drastic steepening above this value caused by a combination of cluster disruption and incompleteness. Rapid cluster disruption for clusters with ages <100 Myr is ruled out for most galaxies.
1511.08311
The Megamaser Cosmology project VIII. A geometric distance to NGC 5765b
Gao, et al
Present a new geometric distance measurement to the megamaser galaxy NGC 5765b. Confirmed the water masers trace a thin, sub parsec Keplerian disk around the nucleus, implying an enclosed mass of 4.55±0.40e7 Msun. Meanwhile, from observations over 2 years, measure the secular drifts of maser features near the systemic velocity of the galaxy with rates between 0.5 and 1.2 km/s/yr. Fitting a warped, thin disk model to these measurements, determine a Hubble constant H0 of 66.0±6.0 km/s/Mpc with the angular-diameter distance to 126.3±11.6 Mpc. Apart from the distance measurement, also investigate some physical properties related to the maser disk in the galaxy. The high-velocity features are spatially distributed into several clumps, which may indicate the existence of a spiral density wave associated with the accretion disk. For the red-shifted features, the envelope defined by the peak maser intensities increases with radius. The profile of the systemic masers in the galaxy is smooth and shows almost no structural changes over the 2 years of monitoring time, which differs form the more variable case of NGC 4258.
1511.08502
How big can a black hole grow?
King
Show that there is a physical limit to the mass of a BH, above which it cannot grow through luminous accretion of gas, and so cannot appear as a quasar or AGN. The limit is M_max~5e10 Msun for typically parameters, but can reach 2.7e11 Msun in extreme cases (maximal prograde spin). The largest BH masses so far found are close but below the limit. The Eddington luminosity ~ 6.5e48 erg/s corresponding to Mmax is remarkable close to the largest AGN bolometric luminosity so far observed. The mass and luminosity limits both rely on a reasonable but currently untestable hypothesis about AGN disk formation, so future observations of extreme SMBH masses can therefore probe fundamental disc physics. BHs can in principle glow their masses above Mmax by non-luminous means such as mergers with other holes, but cannot become luminous accretions again. They might nevertheless be detectable in other ways, for example through gravitational lensing. Show further that BHs with masses~Mmax can probably grow above the values specified by the BH -- host-galaxy scaling relations, in a agreement with observation.
Wednesday, November 25, 2015
Day 1012
Thursday.
1511.07872
Hydrostatic and Caustic mass profiles of galaxy clusters
Maughan, et al
Compare X-ray and caustic mass profiles for a sample of 16 massive galaxy clusters. Assume hydrostatic equilibrium in interpreting the X-ray data, and use large samples of cluster members with redshifts as a basis for applying the caustic technique. The hydrostatic and caustic masses agree to better than 20% on average across the radial range covered by both techniques (~[0.2-1.25]R_500), and to within 5% on average at R_500. The mass profiles were measured independently and do not assume a functional form for either technique. Pervious studies suggest that, at R_500, the hydrostatic and caustic masses are based low and high respectively. Find that the ratio of hydrostatic to caustic mass at R_500 is 1.05±0.06; thus it is larger than 0.9 at ~3 sigma and the combination of under- and over-estimation of the mass by these two techniques is ~10% at most. There is no indication of any dependence of the mass ratio on the X-ray morphology of the clusters, indicating that the hydrostatic masses are not strongly systematically affected by the dynamical state of the clusters. Overall, the results favor a small value of the so-called hydrostatic bias due to non-thermal pressure sources.
1511.07873
Evolution of stellar-to-halo mass ratio at z=0-7 identified by clustering analysis with the Hubble Legacy imaging and early sugary/Hyper Suprime-Cam survey data
Harikane, Ouchi, Ono, More, Saito, Lin, ... et al
Present clustering analysis results from 10,540 LBGs (lyman-break galaxies) at z~4-7 that are identified in a combination of the Hubble legacy deep imaging and the complimentary large-area Subaru/Hyper Suprime-Cam data taken very recently. Measure angular correlation functions of these LBGs at z~4,5,6, and 7, and fit these measurements using HOD models that provide the estimates of halo masses, M_h~(1-20)e11 Msun. The M_h estimates agree with those obtained by previous clustering studies in a UV-magnitude vs. M_h plane, and allow to calculate stellar-to-halo mass ratios (SHMRs) of the LBGs. By comparison with the z~0 SHMR given by SDSS, identify evolution of the SHMR from z~0 to z~4, and z~4 to 7 at the >98% CL. The SHMR decreases by a factor of ~3 from z~0 to 4, and increase by factor of ~5 from z~4 to 7. Obtain the baryon conversion efficiency (BCE) of the LBGs at z~4, and find that the BCE increases with increasing DM halo mass. Finally compare the clustering+HOD estimates with the abundance matching results, and conclude that the M_h estimates of the clustering+HOD analyses agree with those of the simple abundance matching within a factor of 3, and that the agreement is better with those of the sophisticated abundance matching techniques that include sub haloes, incompleteness, and/or star formation rate + stellar mass function evolution.
1511.08083
The Subary FMOS galaxy redshift survey (FastSound). IV. New constraint on gravity theory from redshift space distortions at $z\sim 1.4$
Okumura, HIkage, Totani, et al
Measure the z-space correlation function from a spectroscopic sample of 2830 emission line galaxies from FastSound. The survey, which uses Subaru and covers 1.19<z<1.55, is the first cosmo study at these high redshifts. Detect clear anisotropy due to RSD both in the correlation function as a function of separations parallel and perpendicular to the LoS and its quadrupole moment. RSD has been extensively used to test general relativity on cosmo scales at z<1. Adopting a LCDM cosmo, and using the RSD measurements on scales above 8Mpc/h, obtain the first constraint on the growth rate at the redshift, f(z)sigma8(z)=0.482±0.116 at z~1.4. This corresponds to 4.2 sigma detection of RSD, after marginalizing over the galaxy bias parameter b(z)sigma8(z). The constraint is consistent with the prediction of GR f sigma8~0.392 within the 1-sigma confidence level. Also demonstrate that by combining with the low-z constraints on f sigma8, high-z galaxy surveys like FastSound can be useful to distinguish modified gravity models without relying on CMB anisotropy experiments.
1511.07872
Hydrostatic and Caustic mass profiles of galaxy clusters
Maughan, et al
Compare X-ray and caustic mass profiles for a sample of 16 massive galaxy clusters. Assume hydrostatic equilibrium in interpreting the X-ray data, and use large samples of cluster members with redshifts as a basis for applying the caustic technique. The hydrostatic and caustic masses agree to better than 20% on average across the radial range covered by both techniques (~[0.2-1.25]R_500), and to within 5% on average at R_500. The mass profiles were measured independently and do not assume a functional form for either technique. Pervious studies suggest that, at R_500, the hydrostatic and caustic masses are based low and high respectively. Find that the ratio of hydrostatic to caustic mass at R_500 is 1.05±0.06; thus it is larger than 0.9 at ~3 sigma and the combination of under- and over-estimation of the mass by these two techniques is ~10% at most. There is no indication of any dependence of the mass ratio on the X-ray morphology of the clusters, indicating that the hydrostatic masses are not strongly systematically affected by the dynamical state of the clusters. Overall, the results favor a small value of the so-called hydrostatic bias due to non-thermal pressure sources.
1511.07873
Evolution of stellar-to-halo mass ratio at z=0-7 identified by clustering analysis with the Hubble Legacy imaging and early sugary/Hyper Suprime-Cam survey data
Harikane, Ouchi, Ono, More, Saito, Lin, ... et al
Present clustering analysis results from 10,540 LBGs (lyman-break galaxies) at z~4-7 that are identified in a combination of the Hubble legacy deep imaging and the complimentary large-area Subaru/Hyper Suprime-Cam data taken very recently. Measure angular correlation functions of these LBGs at z~4,5,6, and 7, and fit these measurements using HOD models that provide the estimates of halo masses, M_h~(1-20)e11 Msun. The M_h estimates agree with those obtained by previous clustering studies in a UV-magnitude vs. M_h plane, and allow to calculate stellar-to-halo mass ratios (SHMRs) of the LBGs. By comparison with the z~0 SHMR given by SDSS, identify evolution of the SHMR from z~0 to z~4, and z~4 to 7 at the >98% CL. The SHMR decreases by a factor of ~3 from z~0 to 4, and increase by factor of ~5 from z~4 to 7. Obtain the baryon conversion efficiency (BCE) of the LBGs at z~4, and find that the BCE increases with increasing DM halo mass. Finally compare the clustering+HOD estimates with the abundance matching results, and conclude that the M_h estimates of the clustering+HOD analyses agree with those of the simple abundance matching within a factor of 3, and that the agreement is better with those of the sophisticated abundance matching techniques that include sub haloes, incompleteness, and/or star formation rate + stellar mass function evolution.
1511.08083
The Subary FMOS galaxy redshift survey (FastSound). IV. New constraint on gravity theory from redshift space distortions at $z\sim 1.4$
Okumura, HIkage, Totani, et al
Measure the z-space correlation function from a spectroscopic sample of 2830 emission line galaxies from FastSound. The survey, which uses Subaru and covers 1.19<z<1.55, is the first cosmo study at these high redshifts. Detect clear anisotropy due to RSD both in the correlation function as a function of separations parallel and perpendicular to the LoS and its quadrupole moment. RSD has been extensively used to test general relativity on cosmo scales at z<1. Adopting a LCDM cosmo, and using the RSD measurements on scales above 8Mpc/h, obtain the first constraint on the growth rate at the redshift, f(z)sigma8(z)=0.482±0.116 at z~1.4. This corresponds to 4.2 sigma detection of RSD, after marginalizing over the galaxy bias parameter b(z)sigma8(z). The constraint is consistent with the prediction of GR f sigma8~0.392 within the 1-sigma confidence level. Also demonstrate that by combining with the low-z constraints on f sigma8, high-z galaxy surveys like FastSound can be useful to distinguish modified gravity models without relying on CMB anisotropy experiments.
Tuesday, November 24, 2015
Day 1011
Wednesday.
1511.07377
Combining galaxy and 21cm surveys
Cohn, White, Chang, Holder, Padmanabhan, Doré
Acoustic waves traveling through the early Universe imprint a characteristic scale in the clustering of galaxies, QSOs and inter-galactic gas. This scale can be used as a standard ruler to map the expansion history of the Universe, a technique known as BAO. BAO offer a high-precision, low-systematics means of constraining the cosmo model. The statistical power of BAO measurements can be improved if the 'smearing' of the acoustic feature by non-linear structure formation is undone in a process known as reconstruction. In this paper, use low-order Lagrangian perturbation theory to study the ability of 21 cm experiments to perform reconstruction and how augmenting these surveys with galaxy redshift surveys at relatively low number densities can improve performance. Find that the critical number density which must be achieved in order to benefit 21 cm surveys is set by the linear theory power spectrum near its peak, and corresponds to densities achievable by upcoming surveys of emission line galaxies such as eBOSS and DESI. As part of this work, analyze reconstruction within the framework of Lagrangian perturbation theory with local Lagrangian bias, redshift-space distortions, k-dependent noise and anisotropic filtering schemes.
1511.07377
Combining galaxy and 21cm surveys
Cohn, White, Chang, Holder, Padmanabhan, Doré
Acoustic waves traveling through the early Universe imprint a characteristic scale in the clustering of galaxies, QSOs and inter-galactic gas. This scale can be used as a standard ruler to map the expansion history of the Universe, a technique known as BAO. BAO offer a high-precision, low-systematics means of constraining the cosmo model. The statistical power of BAO measurements can be improved if the 'smearing' of the acoustic feature by non-linear structure formation is undone in a process known as reconstruction. In this paper, use low-order Lagrangian perturbation theory to study the ability of 21 cm experiments to perform reconstruction and how augmenting these surveys with galaxy redshift surveys at relatively low number densities can improve performance. Find that the critical number density which must be achieved in order to benefit 21 cm surveys is set by the linear theory power spectrum near its peak, and corresponds to densities achievable by upcoming surveys of emission line galaxies such as eBOSS and DESI. As part of this work, analyze reconstruction within the framework of Lagrangian perturbation theory with local Lagrangian bias, redshift-space distortions, k-dependent noise and anisotropic filtering schemes.
Monday, November 23, 2015
Day 1010
Tuesday.
1511.06762
Direct imaging of the water snow line at the time of planet formation using two ALMA continuum bands
Banzatti et al
Molecular snow lines in protoplanetary disks have been studied theoretically for decades because of their importance in shaping planetary architectures and compositions. The water snow line lies in the planet formation region at <10 AU, and so far its location has been estimated only indirectly from spatially-unresolved spectroscopy. This work presents a proof-of-concept method to directly image the water snow line in protoplanetary disks through its physical and chemical imprint in the local dust properties. Adopt a physical disk model that includes dust coagulation, fragmentation, direct and a change in fragmentation velocities of a factor 10 between dry silicates and icy grains as found by lab work. Find that the presence of a water snow line leads to a sharp discontinuity in the radial profile of the dust emission spectral index \alpha_mm, due to replenishment of small grains through fragmentation. Use the ALMA simulator to demonstrate that this effect can be observed in protoplanetary disks using spatially-resolved ALMA images in two continuum bands. Explore the model dependence on the disk viscosity and find that the spectral index reveals the water snow line for a wide range of conditions, with opposite trends when the emission is optically thin rather than thick. If the disk viscosity is low (alpha_vic<1e-3) the snow line produces a ring-like structure with a minimum at alpha_mm~2 in the optically thick regime, possibly similar to what has been measured with ALMA in the innermost region of the HL Tau disk.
1511.06762
Direct imaging of the water snow line at the time of planet formation using two ALMA continuum bands
Banzatti et al
Molecular snow lines in protoplanetary disks have been studied theoretically for decades because of their importance in shaping planetary architectures and compositions. The water snow line lies in the planet formation region at <10 AU, and so far its location has been estimated only indirectly from spatially-unresolved spectroscopy. This work presents a proof-of-concept method to directly image the water snow line in protoplanetary disks through its physical and chemical imprint in the local dust properties. Adopt a physical disk model that includes dust coagulation, fragmentation, direct and a change in fragmentation velocities of a factor 10 between dry silicates and icy grains as found by lab work. Find that the presence of a water snow line leads to a sharp discontinuity in the radial profile of the dust emission spectral index \alpha_mm, due to replenishment of small grains through fragmentation. Use the ALMA simulator to demonstrate that this effect can be observed in protoplanetary disks using spatially-resolved ALMA images in two continuum bands. Explore the model dependence on the disk viscosity and find that the spectral index reveals the water snow line for a wide range of conditions, with opposite trends when the emission is optically thin rather than thick. If the disk viscosity is low (alpha_vic<1e-3) the snow line produces a ring-like structure with a minimum at alpha_mm~2 in the optically thick regime, possibly similar to what has been measured with ALMA in the innermost region of the HL Tau disk.
Day 1009
Wednesday. Thursday. Friday. Monday.
1511.05969
Parameter inference with estimated covariance matrices
Sellentin, Heavens
When inferring parameters from a Gaussian-distributed data set by computing a likelihood, a covariance matrix is needed that describes the data errors and their correlations. If the covariance matrix is not known a priori, it may be estimated and thereby becomes a random object with some intrinsic uncertainty itself. Show how to infer parameters in the presence of such an estimated covariance matrix, by marginalizing over the true covariance matrix, conditioned on its estimated value. This leads to a likelihood function that is no longer Gaussian, but rather an adapted version of a multivariate t-distribution, which has the same numerical complexity as the multivariate Gaussian. As expected, marginalization over the true covariance matrix improves inference when compared with Hartlap+'s method, which uses an unbiased estimate of the inverse covariance matrix but still assumes that the likelihood is Gaussian.
1511.05983
Neutrino mass limits: robust information from the power spectrum of galaxy surveys
Cuesta, Niro, Verde
Present cosmo upper limits on the sum of active neutrino masses using large-scale power spectrum data from the WiggleZ DarkEnergy Survey and from SDSS-DR7 sample of LRGs. Combining measurements on the CMB temperature and polarization anisotropies by the Planck satellite together with WiggleZ power spectrum results in a neutrino mass bound of 0.43 eV at 95% C.L., while replacing WiggleZ by the SDSS-DR7 LRG PS, the 95% C.L. bound on the sum of neutrino masses improves to 0.17 eV. Adding BAO distance scale measurements, the neutrino mass upper limits greatly improve, since BAO data break degeneracies in parameter space. Within a LCDM model, find an upper limit of 0.11 eV (0.15 eV) at 95% C.L., when using SDSS-DR7 LRG (WiggleZ) together with BAO and Planck. The addition of BAO data makes the neutrino mass upper limit robust, showing only a weak dependence on the PS used. Also quantify the dependence of neutrino mass limit reported here on the CMB lensing information. The tighter upper limit (0.11 eV) obtained with SDSS-DR7 LRG is very close to that recently obtained using Lyman-alpha clustering data, yet uses a completely different probe and redshift range, further supporting the robustness of the constraint. This constraint puts under some pressure the inverted mass hierarchy and favors the normal hierarchy.
1511.05994
Gravitational-wave cosmology across 29 decades in frequency
Lanky et al
Quantum fluctuations of the gravitational field in the early Universe, amplified by inflation, produce a primordial gravitational-wave background across a broad frequency band. Derive constraints on the spectrum of this gravitational radiation, and hence on theories of the early Universe, by combining experiments that cover 29 orders of magnitude in frequency. These include Planck observations of cosmic microwave background temperature and polarization power spectra and lensing, together with BAO and BBN measurements, as well as new pulsar timing array and ground-based interferometer limits. While individual experiment constrain the gravitational-wave energy density in specific frequency bands, the combination of experiments allows to constrain cosmological parameters, including the inflationary spectral index, n_t, and the tensor-to-scalar ratio, r. Results from individual experiments include the most stringent nanohertz limit of the primordial background to date from the Parkes Pulsar Timing Array, Omega_gw(f) < 2.3e-10. Observations of the CMB alone limit the gravitational-wave spectral index at 95% confidence to n_t<~5 for a r=0.11. However, the combination of all the above experiments limits n_t<0.36. Further Advanced LIGO observations are expected to further constraint n_t<0.34 by 2020. When CMB experiments detect a non-zero r, the results will imply even more stringent constraints on n_t and hence theories of the early Universe.
1511.06741
The sparkling Universe: a scenario for cosmic void motions
Ceccarelli, et al
Perform a statistical study of the global motion of cosmic voids using both a numerical sim and observational data. Analyze their relation to LS mass flows and the physical effects that drive those motions. Analyze the bulk motions of voids, defined by the mean velocity of haloes in the surrounding shells in the numerical simulation, and by galaxies in SDSS DR7. Find void mean bulk velocities close to 400 km/s, comparable to those of haloes (~500-600 km/s), depending on void size and the LS environment. Statistically, small voids move faster than large ones, and voids in relatively higher density environments have higher bulk velocities than those placed in large underdense regions. Analyze the mean mass density around voids finding LS over densities (under densities) along (opposite to) the void motion direction, suggesting that void motions respond to a pull-push mechanism. This contrasts with massive cluster motions who are mainly governed by the pull of the LS overdense regions. The analysis of void pairwise velocities shows how their relative motions are generated by LS density fluctuations. In agreement with linear theory, voids embedded in low (high) density regions mutually recede (attract) each other, providing the general mechanism to understand the bimodal behavior of void motions. In order to compare the theoretical results and the observations, infer void motions in the SDSS using near theory, finding that the estimated observational void motions are in statistical agreement with the results of the simulation. Regarding LS flows, results suggest a scenario of galaxies and galaxy systems flowing away from void centers with the additional, and more relevant, contribution of the void bulk motion to the total velocity.
1511.05969
Parameter inference with estimated covariance matrices
Sellentin, Heavens
When inferring parameters from a Gaussian-distributed data set by computing a likelihood, a covariance matrix is needed that describes the data errors and their correlations. If the covariance matrix is not known a priori, it may be estimated and thereby becomes a random object with some intrinsic uncertainty itself. Show how to infer parameters in the presence of such an estimated covariance matrix, by marginalizing over the true covariance matrix, conditioned on its estimated value. This leads to a likelihood function that is no longer Gaussian, but rather an adapted version of a multivariate t-distribution, which has the same numerical complexity as the multivariate Gaussian. As expected, marginalization over the true covariance matrix improves inference when compared with Hartlap+'s method, which uses an unbiased estimate of the inverse covariance matrix but still assumes that the likelihood is Gaussian.
1511.05983
Neutrino mass limits: robust information from the power spectrum of galaxy surveys
Cuesta, Niro, Verde
Present cosmo upper limits on the sum of active neutrino masses using large-scale power spectrum data from the WiggleZ DarkEnergy Survey and from SDSS-DR7 sample of LRGs. Combining measurements on the CMB temperature and polarization anisotropies by the Planck satellite together with WiggleZ power spectrum results in a neutrino mass bound of 0.43 eV at 95% C.L., while replacing WiggleZ by the SDSS-DR7 LRG PS, the 95% C.L. bound on the sum of neutrino masses improves to 0.17 eV. Adding BAO distance scale measurements, the neutrino mass upper limits greatly improve, since BAO data break degeneracies in parameter space. Within a LCDM model, find an upper limit of 0.11 eV (0.15 eV) at 95% C.L., when using SDSS-DR7 LRG (WiggleZ) together with BAO and Planck. The addition of BAO data makes the neutrino mass upper limit robust, showing only a weak dependence on the PS used. Also quantify the dependence of neutrino mass limit reported here on the CMB lensing information. The tighter upper limit (0.11 eV) obtained with SDSS-DR7 LRG is very close to that recently obtained using Lyman-alpha clustering data, yet uses a completely different probe and redshift range, further supporting the robustness of the constraint. This constraint puts under some pressure the inverted mass hierarchy and favors the normal hierarchy.
1511.05994
Gravitational-wave cosmology across 29 decades in frequency
Lanky et al
Quantum fluctuations of the gravitational field in the early Universe, amplified by inflation, produce a primordial gravitational-wave background across a broad frequency band. Derive constraints on the spectrum of this gravitational radiation, and hence on theories of the early Universe, by combining experiments that cover 29 orders of magnitude in frequency. These include Planck observations of cosmic microwave background temperature and polarization power spectra and lensing, together with BAO and BBN measurements, as well as new pulsar timing array and ground-based interferometer limits. While individual experiment constrain the gravitational-wave energy density in specific frequency bands, the combination of experiments allows to constrain cosmological parameters, including the inflationary spectral index, n_t, and the tensor-to-scalar ratio, r. Results from individual experiments include the most stringent nanohertz limit of the primordial background to date from the Parkes Pulsar Timing Array, Omega_gw(f) < 2.3e-10. Observations of the CMB alone limit the gravitational-wave spectral index at 95% confidence to n_t<~5 for a r=0.11. However, the combination of all the above experiments limits n_t<0.36. Further Advanced LIGO observations are expected to further constraint n_t<0.34 by 2020. When CMB experiments detect a non-zero r, the results will imply even more stringent constraints on n_t and hence theories of the early Universe.
1511.06741
The sparkling Universe: a scenario for cosmic void motions
Ceccarelli, et al
Perform a statistical study of the global motion of cosmic voids using both a numerical sim and observational data. Analyze their relation to LS mass flows and the physical effects that drive those motions. Analyze the bulk motions of voids, defined by the mean velocity of haloes in the surrounding shells in the numerical simulation, and by galaxies in SDSS DR7. Find void mean bulk velocities close to 400 km/s, comparable to those of haloes (~500-600 km/s), depending on void size and the LS environment. Statistically, small voids move faster than large ones, and voids in relatively higher density environments have higher bulk velocities than those placed in large underdense regions. Analyze the mean mass density around voids finding LS over densities (under densities) along (opposite to) the void motion direction, suggesting that void motions respond to a pull-push mechanism. This contrasts with massive cluster motions who are mainly governed by the pull of the LS overdense regions. The analysis of void pairwise velocities shows how their relative motions are generated by LS density fluctuations. In agreement with linear theory, voids embedded in low (high) density regions mutually recede (attract) each other, providing the general mechanism to understand the bimodal behavior of void motions. In order to compare the theoretical results and the observations, infer void motions in the SDSS using near theory, finding that the estimated observational void motions are in statistical agreement with the results of the simulation. Regarding LS flows, results suggest a scenario of galaxies and galaxy systems flowing away from void centers with the additional, and more relevant, contribution of the void bulk motion to the total velocity.
Tuesday, November 17, 2015
Day 1008
Monday. Tuesday.
1511.04075
Cluster-void degeneracy breaking: dark energy, Planck and the largest cluster & Void
Sahlin, Zubeldía, Silk
Combining galaxy cluster and void abundances breaks the degeneracy between mean matter density Omega_m and power spectrum normalization sigma8. In a first for voids, constrain Omega_m=0.21±0.10 and sigma_8=0.95±0.21 for a flat LCDM universe, using extreme-value statistics on the claimed largest cluster and void. The Planck-consistent results detect DE with two objects, independently of other DE probes. Cluster void studies also offer complementarity in scale, density, and non-linearity - of particular interest for testing modified-gravity models.
1511.04086
Ubiquitous time variability of integrated stellar populations
Conroy, van Dokkum, Choi
Long period variable stars arise in the final stages of the asymptotic giant branch phase of stellar evolution. They have periods of up to ~1000d and amplitudes that can exceed a factor of three in the I-band flux. These stars pulsate predominantly in their fundamental mode, which is a function of mass and radius, and so the pulsation periods are sensitive to the age of the underlying stellar population. The overall number of long period variables in a population is directly related to their lifetime, which is difficult to predict from first principles because of uncertainties associated with stellar mass-loss and convective mixing. The time variability of these stars has not been previously taken into account when molding the spectral energy distributions of galaxies. Construct time-dependent stellar population models that include the effects of long period variable stars, and report the ubiquitous detection of this expected 'pixel shimmer' in the massive metal-rich galaxy M87. The pixel light curves display a variety of behaviors, including linearly rising and falling curves, semi-periodic curves, and sudden increases or decreases in the flux level. The observed variation of 0.1-1% is very well matched to the predictions of the models. The data provide a strong and novel constraint on the properties of variable stars in an old and metal-rich stellar population, and infer that the lifetime of long period variables in M87 is shorted by approximately 30% compared to predictions from the latest stellar evolution models.
1511.04090
Inverted initial conditions: exploring the growth of cosmic structure and voids
Pontzen, Slosar, Roth, Peiris
Introduce and explore "paired" cosmo sims. A pair consists of an A and B simulation with initial conditions related by the inversion delta_A(x,t_i)=-delta_B(x,t_i) (under densities substituted for over densities and vice versa). Argue that the technique is valuable for improving the understanding of cosmic structure formation. The A and B fields are by definition equally likely draws from LCDM ICs, and in the linear regime evolve identically up to the overall sign. As NL evolution takes hold, a region that collapses to form a halo in simulation A will tend to expand to create a void in simulation B. Applications include (i) contrasting the growth of A-haloes and B-voids to test excursion-set theories of structure formation; (ii) cross-correlating the density field of the A and B universes as a novel test for perturbation theory,; and (iii) canceling error terms by averaging PS between the two boxes. Generalizations of the method to more elaborate field transformations are suggested.
1511.04093
The story of supernova 'Refsdal' told by MUSE
Grillo, .. Suyu, ... Treu, et al
SN at z=1.489; DDT program at VLT gives 117 secure redshifts, 68 galaxy cluster members, and 18 multiple images belonging to 7 BG, lensed sources between 1.230 and 3.703. Select a sample of 300 (164 spec and 136 photo-z) cluster members, within ~500 kpc from BCG, and a set of 88 reliable multiple images associated to 10 different background source galaxies and 18 distinct knots in the spiral galaxy hosting SN 'Refsdal'. Exploit this information to build 6 detailed SL models, the best of which reproduces the observed positions of the multiple images with a rms offset of only 0.26". Use these models to quantify the statistical and systematic errors on the predicted values of magnification and time delay of the next emerging image of SN 'Refsdal'. Find that its peak luminosity should be approximately 20% fainter that the dimmest (S4) of the previously detected images but above the detection limit of the planned HST/WFC3 follow-up and should occur between March and June 2016. Present the 2d reconstruction of the cluster mass density distribution and of the SN 'Refsdal' host galaxy surface brightness distribution. Outline the roadmap towards even better strong lensing models with a synergetic MUSE and HST effort.
1511.04095
Bulge formation via mergers in cosmological simulations
Brooks, Christensen
[Review article for "Galactic Bulges"] Galaxy mergers have long been assumed to produce classical bulges in disk galaxies. Under this bulge-formation model, though, the high rates of mergers in CDM galaxy formation theory predict many more classical bulges than are observed. Furthermore, simulations of galaxy formation continue to generally produce too massive of bulges. Feedback offers a promising avenue for reducing merger-driven bulge growth by maintaining high gas fractions in galaxies and ejecting low-angular momentum gas driven to the centers of galaxies. After reviewing the results of relevant research that has been published to date, use cosmo sims to explore the ability of feedback to reduce or even prevent bulge growth during mergers. In dwarf galaxies, mergers actually reduce the central concentration of galaxies as the induced burst of SF drives out low angular momentum material. This results shows the potential for feedback to reduce central mass growth. However, also demonstrate that it is very difficult for current stellar feedback models to reproduce the small bulges observed in more massive disk galaxies like the MW. Argue that feedback models need to be improved, or an additional source of feedback such as AGN is necessary to generate the required outflows.
1511.04391
Measuring Baryon Acoustic Oscillations from the clustering of voids
Liang, ... Kitaura, et al
Investigate the necessary methodology to optimally measure the BAO signal ,from voids based on galaxy redshift catalogues. To this end, study the dependence of the BAO signal on the population of voids classified by their sizes. Find for the first time the characteristic features of the correlation function of voids including the first robust detection of BAOs in mock galaxy catalogues. These show an anti-correlation around the scale corresponding to the smallest size of voids in the sample (the void exclusion effect), and dips at both sides of the BAO peak, which can be used to determine the significance of the BAO signal without any prior model. Furthermore, the analysis demonstrates that there is a scale dependent bias for different populations of voids depending on the radius, with the peculiar property that the void population with the largest BAO significance corresponds to tracers with approximately zero bias on the largest scales. Further investigate the methodology on an additional set of1000 realistic mock galaxy catalogues reproducing BOSS CMASS DR11 data, to control the impact of sky mask and radial selection function. The solution is based on generating voids from randoms including the same survey geometry and completeness, and a post-rpcoessing cleaning procedure in the holes and at the boundaries of the survey. The methodology and optimal selection of void populations validated in this work have been used to perform the first BAO detection from voids in observations, presented in a companion paper.
1511.04405
Signatures of the primordial universe from its emptiness
Kit aura, et al
Propose to measure BAOs from the minima of the density field. based on two sets of accurate mock halo catalogues with and without BAOs in the seed ICs, demonstrate that the BAO signal cannot be obtained from the clustering of classical disjoint voids, but is clearly detected from overlapping voids. The latter represent an estimate of all throughs of the density field. Compute them from the empty circumsphere centers constrained by tetrahedra of galaxies using Delaunay triangulation. The theoretical models based on an unprecedented large set of detained simulated void catalogues are remarkably well confirmed by observational data. Use the largest recently publicly available sample of LRGs from BOSS DR11 to unveil for the first time a >3sigma BAO detection from voids in observations. Since voids are nearly isotropically expanding regions, their center represent the most quiets places in the Universe, keeping in memory the cosmos origin, and providing a new promising window in the analysis of the cosmo LSS from galaxy survey.
1511.04075
Cluster-void degeneracy breaking: dark energy, Planck and the largest cluster & Void
Sahlin, Zubeldía, Silk
Combining galaxy cluster and void abundances breaks the degeneracy between mean matter density Omega_m and power spectrum normalization sigma8. In a first for voids, constrain Omega_m=0.21±0.10 and sigma_8=0.95±0.21 for a flat LCDM universe, using extreme-value statistics on the claimed largest cluster and void. The Planck-consistent results detect DE with two objects, independently of other DE probes. Cluster void studies also offer complementarity in scale, density, and non-linearity - of particular interest for testing modified-gravity models.
1511.04086
Ubiquitous time variability of integrated stellar populations
Conroy, van Dokkum, Choi
Long period variable stars arise in the final stages of the asymptotic giant branch phase of stellar evolution. They have periods of up to ~1000d and amplitudes that can exceed a factor of three in the I-band flux. These stars pulsate predominantly in their fundamental mode, which is a function of mass and radius, and so the pulsation periods are sensitive to the age of the underlying stellar population. The overall number of long period variables in a population is directly related to their lifetime, which is difficult to predict from first principles because of uncertainties associated with stellar mass-loss and convective mixing. The time variability of these stars has not been previously taken into account when molding the spectral energy distributions of galaxies. Construct time-dependent stellar population models that include the effects of long period variable stars, and report the ubiquitous detection of this expected 'pixel shimmer' in the massive metal-rich galaxy M87. The pixel light curves display a variety of behaviors, including linearly rising and falling curves, semi-periodic curves, and sudden increases or decreases in the flux level. The observed variation of 0.1-1% is very well matched to the predictions of the models. The data provide a strong and novel constraint on the properties of variable stars in an old and metal-rich stellar population, and infer that the lifetime of long period variables in M87 is shorted by approximately 30% compared to predictions from the latest stellar evolution models.
1511.04090
Inverted initial conditions: exploring the growth of cosmic structure and voids
Pontzen, Slosar, Roth, Peiris
Introduce and explore "paired" cosmo sims. A pair consists of an A and B simulation with initial conditions related by the inversion delta_A(x,t_i)=-delta_B(x,t_i) (under densities substituted for over densities and vice versa). Argue that the technique is valuable for improving the understanding of cosmic structure formation. The A and B fields are by definition equally likely draws from LCDM ICs, and in the linear regime evolve identically up to the overall sign. As NL evolution takes hold, a region that collapses to form a halo in simulation A will tend to expand to create a void in simulation B. Applications include (i) contrasting the growth of A-haloes and B-voids to test excursion-set theories of structure formation; (ii) cross-correlating the density field of the A and B universes as a novel test for perturbation theory,; and (iii) canceling error terms by averaging PS between the two boxes. Generalizations of the method to more elaborate field transformations are suggested.
1511.04093
The story of supernova 'Refsdal' told by MUSE
Grillo, .. Suyu, ... Treu, et al
SN at z=1.489; DDT program at VLT gives 117 secure redshifts, 68 galaxy cluster members, and 18 multiple images belonging to 7 BG, lensed sources between 1.230 and 3.703. Select a sample of 300 (164 spec and 136 photo-z) cluster members, within ~500 kpc from BCG, and a set of 88 reliable multiple images associated to 10 different background source galaxies and 18 distinct knots in the spiral galaxy hosting SN 'Refsdal'. Exploit this information to build 6 detailed SL models, the best of which reproduces the observed positions of the multiple images with a rms offset of only 0.26". Use these models to quantify the statistical and systematic errors on the predicted values of magnification and time delay of the next emerging image of SN 'Refsdal'. Find that its peak luminosity should be approximately 20% fainter that the dimmest (S4) of the previously detected images but above the detection limit of the planned HST/WFC3 follow-up and should occur between March and June 2016. Present the 2d reconstruction of the cluster mass density distribution and of the SN 'Refsdal' host galaxy surface brightness distribution. Outline the roadmap towards even better strong lensing models with a synergetic MUSE and HST effort.
1511.04095
Bulge formation via mergers in cosmological simulations
Brooks, Christensen
[Review article for "Galactic Bulges"] Galaxy mergers have long been assumed to produce classical bulges in disk galaxies. Under this bulge-formation model, though, the high rates of mergers in CDM galaxy formation theory predict many more classical bulges than are observed. Furthermore, simulations of galaxy formation continue to generally produce too massive of bulges. Feedback offers a promising avenue for reducing merger-driven bulge growth by maintaining high gas fractions in galaxies and ejecting low-angular momentum gas driven to the centers of galaxies. After reviewing the results of relevant research that has been published to date, use cosmo sims to explore the ability of feedback to reduce or even prevent bulge growth during mergers. In dwarf galaxies, mergers actually reduce the central concentration of galaxies as the induced burst of SF drives out low angular momentum material. This results shows the potential for feedback to reduce central mass growth. However, also demonstrate that it is very difficult for current stellar feedback models to reproduce the small bulges observed in more massive disk galaxies like the MW. Argue that feedback models need to be improved, or an additional source of feedback such as AGN is necessary to generate the required outflows.
1511.04391
Measuring Baryon Acoustic Oscillations from the clustering of voids
Liang, ... Kitaura, et al
Investigate the necessary methodology to optimally measure the BAO signal ,from voids based on galaxy redshift catalogues. To this end, study the dependence of the BAO signal on the population of voids classified by their sizes. Find for the first time the characteristic features of the correlation function of voids including the first robust detection of BAOs in mock galaxy catalogues. These show an anti-correlation around the scale corresponding to the smallest size of voids in the sample (the void exclusion effect), and dips at both sides of the BAO peak, which can be used to determine the significance of the BAO signal without any prior model. Furthermore, the analysis demonstrates that there is a scale dependent bias for different populations of voids depending on the radius, with the peculiar property that the void population with the largest BAO significance corresponds to tracers with approximately zero bias on the largest scales. Further investigate the methodology on an additional set of1000 realistic mock galaxy catalogues reproducing BOSS CMASS DR11 data, to control the impact of sky mask and radial selection function. The solution is based on generating voids from randoms including the same survey geometry and completeness, and a post-rpcoessing cleaning procedure in the holes and at the boundaries of the survey. The methodology and optimal selection of void populations validated in this work have been used to perform the first BAO detection from voids in observations, presented in a companion paper.
1511.04405
Signatures of the primordial universe from its emptiness
Kit aura, et al
Propose to measure BAOs from the minima of the density field. based on two sets of accurate mock halo catalogues with and without BAOs in the seed ICs, demonstrate that the BAO signal cannot be obtained from the clustering of classical disjoint voids, but is clearly detected from overlapping voids. The latter represent an estimate of all throughs of the density field. Compute them from the empty circumsphere centers constrained by tetrahedra of galaxies using Delaunay triangulation. The theoretical models based on an unprecedented large set of detained simulated void catalogues are remarkably well confirmed by observational data. Use the largest recently publicly available sample of LRGs from BOSS DR11 to unveil for the first time a >3sigma BAO detection from voids in observations. Since voids are nearly isotropically expanding regions, their center represent the most quiets places in the Universe, keeping in memory the cosmos origin, and providing a new promising window in the analysis of the cosmo LSS from galaxy survey.
Friday, November 13, 2015
Day 1007
Friday.
1511.03659
He II Proximity effect and the lifetime of quasars
Khrykin, Hennawi, McQuinn, Worseck
The lifetime of quasars is fundamental for understanding the growth of SMBHs, and is an important ingredient in models of the reionization of the IGM. However, despite various attempts to determine quasar lifetimes, current estimates from a variety of methods are uncertain by orders of magnitude. This work combines cosmo hydro sims and 1d radiative transfer to investigate the structure and evolution of the He II Lyalpha proximity zones around quasars at z~3-4. Show that the time evolution in the proximity zone can be described by a simple analytical model for the approach of the He II fraction x_HeII(t) to ionization equilibrium, and use this picture to illustrate how the transmission profile depends on the quasar lifetime, quasar UV luminosity, and the ionization state of he in the ambient IGM (i.e. the average He II fraction, or equivalently the metagalactic He II ionizing background). A significant degeneracy exists between the lifetime and the average He II fraction, however the latter can be determined from measurements of the He II Lya optical depth far from quasars, allowing the lifetime to be measured. Advocate stacking existing He II quasar spectra at z~3, and show that the shape of this average proximity zone profile is sensitive to lifetimes as long as ~30 Myr. At higher redshift z~4 where the He II fraction is poorly constrained, degeneracies will make it challenging to determine these parameters independently. The analytical model for He II proximity zones should also provide a useful description of the properties of H I proximity ones around quasars at z~6-7.
1511.03662
The mass-sheet degeneracy and time-delay cosmography: analysis of the strong lens RXJ1131-1231
Birder, Amara, Rrefregier
Present extended modeling of the SL RXJ1131-1231 with archival data in two HST bands in combination with existing LoS contribution and velocity dispersion estimates. Focus on the accuracy and reliability of the source reconstruction scale and lens model assumptions and its implication on time-delay cosmography. Map out the mass-sheet degeneracy and especially the degeneracy pointed out by Schneider and Sluse (2013) using the source reconstruction scale. In a second step, fold in velocity dispersion and external convergence measurements. Then infer angular diameter distance relations for the time-delays without cosmo priors. For a flat LCDM cosmology, these constraints lead to constraints of the Hubble constant H0 as a function of the matter density Omega_m in the form of H0=H0*/[1+0.5(Omega_m=Omega_m*]±5% with H0*=71.7±3.6 km/s/Mpc being the value for H0 at Omega_m*=0.3. This is a significant improvement in the uncertainty of the lens modeling and is consistent with recent CMB measurements. Describe the full cosmological information of the lens system data in an analytic form such that this information can be combined with other cosmo probes.
1511.03734
The SPLASH survey: quiescent galaxies are more strongly clustered but are not necessarily located in high-density environments
Lin, Capak, et al
Study the environments of galaxies via galaxy density and clustering up to z~2.5. The clustering strength of quiescent galaxies exceeds that of SF galaxies, implying that quiescent galaxies are preferentially located in more massive haloes. When using local density measurement, find a clear positive quiescent fraction -- density relation at z<1, consistent with earlier results. However, the quiescent fraction -- density relation reverses its trend at intermediate redshifts (1<z<1.5) with marginal significance (<1.8 sigma), and is found to be scale dependent (1.6 sigma). The lower fraction of quiescent galaxies seen in large-scale dense environments, if confirmed to be true, may be associated with the fact that the SF can be more easily sustained via cold stream accretion in 'large-scale' high-density regions, preventing galaxies from permanent quenching. Finally at z>1.5, the quiescent fraction depends little on the local density, even though clustering shows that quiescent galaxies are in more massive halos. Argue that at high z the typical halo size falls below 1e13 Msun, where intrinsically the local density measurements are so varied that they do not trace the halo mass. The results thus suggest that in the high-z Universe, halo mass may be the key in quenching the SF in galaxies, rather than the conventionally measured galaxy density.
1511.03659
He II Proximity effect and the lifetime of quasars
Khrykin, Hennawi, McQuinn, Worseck
The lifetime of quasars is fundamental for understanding the growth of SMBHs, and is an important ingredient in models of the reionization of the IGM. However, despite various attempts to determine quasar lifetimes, current estimates from a variety of methods are uncertain by orders of magnitude. This work combines cosmo hydro sims and 1d radiative transfer to investigate the structure and evolution of the He II Lyalpha proximity zones around quasars at z~3-4. Show that the time evolution in the proximity zone can be described by a simple analytical model for the approach of the He II fraction x_HeII(t) to ionization equilibrium, and use this picture to illustrate how the transmission profile depends on the quasar lifetime, quasar UV luminosity, and the ionization state of he in the ambient IGM (i.e. the average He II fraction, or equivalently the metagalactic He II ionizing background). A significant degeneracy exists between the lifetime and the average He II fraction, however the latter can be determined from measurements of the He II Lya optical depth far from quasars, allowing the lifetime to be measured. Advocate stacking existing He II quasar spectra at z~3, and show that the shape of this average proximity zone profile is sensitive to lifetimes as long as ~30 Myr. At higher redshift z~4 where the He II fraction is poorly constrained, degeneracies will make it challenging to determine these parameters independently. The analytical model for He II proximity zones should also provide a useful description of the properties of H I proximity ones around quasars at z~6-7.
1511.03662
The mass-sheet degeneracy and time-delay cosmography: analysis of the strong lens RXJ1131-1231
Birder, Amara, Rrefregier
Present extended modeling of the SL RXJ1131-1231 with archival data in two HST bands in combination with existing LoS contribution and velocity dispersion estimates. Focus on the accuracy and reliability of the source reconstruction scale and lens model assumptions and its implication on time-delay cosmography. Map out the mass-sheet degeneracy and especially the degeneracy pointed out by Schneider and Sluse (2013) using the source reconstruction scale. In a second step, fold in velocity dispersion and external convergence measurements. Then infer angular diameter distance relations for the time-delays without cosmo priors. For a flat LCDM cosmology, these constraints lead to constraints of the Hubble constant H0 as a function of the matter density Omega_m in the form of H0=H0*/[1+0.5(Omega_m=Omega_m*]±5% with H0*=71.7±3.6 km/s/Mpc being the value for H0 at Omega_m*=0.3. This is a significant improvement in the uncertainty of the lens modeling and is consistent with recent CMB measurements. Describe the full cosmological information of the lens system data in an analytic form such that this information can be combined with other cosmo probes.
1511.03734
The SPLASH survey: quiescent galaxies are more strongly clustered but are not necessarily located in high-density environments
Lin, Capak, et al
Study the environments of galaxies via galaxy density and clustering up to z~2.5. The clustering strength of quiescent galaxies exceeds that of SF galaxies, implying that quiescent galaxies are preferentially located in more massive haloes. When using local density measurement, find a clear positive quiescent fraction -- density relation at z<1, consistent with earlier results. However, the quiescent fraction -- density relation reverses its trend at intermediate redshifts (1<z<1.5) with marginal significance (<1.8 sigma), and is found to be scale dependent (1.6 sigma). The lower fraction of quiescent galaxies seen in large-scale dense environments, if confirmed to be true, may be associated with the fact that the SF can be more easily sustained via cold stream accretion in 'large-scale' high-density regions, preventing galaxies from permanent quenching. Finally at z>1.5, the quiescent fraction depends little on the local density, even though clustering shows that quiescent galaxies are in more massive halos. Argue that at high z the typical halo size falls below 1e13 Msun, where intrinsically the local density measurements are so varied that they do not trace the halo mass. The results thus suggest that in the high-z Universe, halo mass may be the key in quenching the SF in galaxies, rather than the conventionally measured galaxy density.
Wednesday, November 11, 2015
Day 1006
Thursday.
Nature 527, 204-207
A small nearby star with an Earth-like planet
Zachary et al
M-dwarf stars -- H-burning stars that are smaller than 60^ of the size of the Sun -- are the most common class of star in our Galaxy and outnumber Sun-like stars by a ratio of 12:1. Recent results have shown that M dwarfs host Earth-sized planets in great numbers: the average number of M-dwarf plants that are between 0.5 to 1.5 times the size of Earth is at least 1.4 per star. The nearest such planets known to transit their star are 39 parsecs away, too distant for detailed follow-up observations to measure the planatery masses or to study their atmospheres. Here, report observations of GJ 1132b, a planet with a size of 1.2 Earth radii that is transiting a mall star 12 pc away. Doppler mass measurement yields a density consistent with an Earth-like bulk composition, similar to the compositions of the 6 known exoplanets with masses less than 6x that of the Earth and precisely measured densities. Receiving 19x more stellar radiation than the Earth, the planet is too hot to be habitable but is cool enough to support a substantial atmosphere, one that has probably been considerably depleted of H. Because the host star is nearby and only 21% the radius of the Sun, existing and upcoming telescopes will be able to observe the composition and dynamics of the planetary atmosphere.
1511.03284
Revisiting the classics: Is [Mg/Fe] a good proxy for galaxy formation time-scales?
Martín-Navarro
In the local Universe, massive early-type galaxies exhibit enhanced [Mg/Fe] ratios, which has been traditionally interpreted as the result of a rapid (tau<1 Gyr) collapse. However, recent claims of a non-universal, steep IMF call for a revision of this standard interpretation. In the present work, show how the simultaneous consideration of a high [Mg/Fe] and a steep IMF slope would imply unreasonably short (tau~7 Myr) and intense (SFR~1e5 Msun/yr) formation events for massive early-type galaxies. Discuss possible caveats and explanations to this apparent inconsistency, and suggest that further IMF determinations, both in the local Universe and at high z, are necessary to better understand the problem.
1511.03391
Crowdsourcing quality control for Dark Energy Survey images
Melchior, Sheldon, et al
Developed a crowdsourcing web application for image quality control employed by DES. Dubbed the "DES exposure checker", it renders science-grade images directly to a web browser and allows users to mark problematic features from a set of predefined classes. Users can also generate custom labels and thus help identify previously unknown problem classes. User reports are fed back to hardware and software experts to help mitigate and eliminate recognized issues. Report on the implementation of the application and the experience with its over 100 users, the majority of which are professional or prospective astronomers but not data management experts. Discuss aspects of user training and engagement, and demonstrate how problem reports have been pivotal to rapidly correct artifacts which would likely have been too subtle or infrequent to be recognized otherwise. Conclude with a number of important lessons learned, suggest possible improvements, and recommend this collective exploratory approach for future astronomical surveys or wither extensive data sets wit a sufficiently large user base. Also release open-source code of the web application and host and online demo version.
1511.03594
The Gini Coefficient as a tool for image family identification in strong lensing systems with multiple images
Florian, Gladers, Li, Sharon
The sample of cosmo SL systems has been strongly growing in recent years; the sample will reach into the thousands with the advent of the next generation of space-based survey telescopes. The accuracy of SL models relies on robust ID of multiple image families of lensed galaxies. For the most massive lenses, often more than one background galaxy is magnified and multiply-imaged, and even in the cases of only a single lensed source, identification of counter images is not always robust. Recently, it was shown that the Gini coefficient in space-telescope-quality imaging is a measurement of galaxy morphology that is relatively well-preserved by strong gravitational lensing. Here, investigate its usefulness as a diagnostic for the purposes of image family identification and show that it can remove some of the degeneracies encountered when using color as the sole diagnostic, and can do so without the need for additional observations since whenever a color is available, two Gini coefficients are as well.
Nature 527, 204-207
A small nearby star with an Earth-like planet
Zachary et al
M-dwarf stars -- H-burning stars that are smaller than 60^ of the size of the Sun -- are the most common class of star in our Galaxy and outnumber Sun-like stars by a ratio of 12:1. Recent results have shown that M dwarfs host Earth-sized planets in great numbers: the average number of M-dwarf plants that are between 0.5 to 1.5 times the size of Earth is at least 1.4 per star. The nearest such planets known to transit their star are 39 parsecs away, too distant for detailed follow-up observations to measure the planatery masses or to study their atmospheres. Here, report observations of GJ 1132b, a planet with a size of 1.2 Earth radii that is transiting a mall star 12 pc away. Doppler mass measurement yields a density consistent with an Earth-like bulk composition, similar to the compositions of the 6 known exoplanets with masses less than 6x that of the Earth and precisely measured densities. Receiving 19x more stellar radiation than the Earth, the planet is too hot to be habitable but is cool enough to support a substantial atmosphere, one that has probably been considerably depleted of H. Because the host star is nearby and only 21% the radius of the Sun, existing and upcoming telescopes will be able to observe the composition and dynamics of the planetary atmosphere.
1511.03284
Revisiting the classics: Is [Mg/Fe] a good proxy for galaxy formation time-scales?
Martín-Navarro
In the local Universe, massive early-type galaxies exhibit enhanced [Mg/Fe] ratios, which has been traditionally interpreted as the result of a rapid (tau<1 Gyr) collapse. However, recent claims of a non-universal, steep IMF call for a revision of this standard interpretation. In the present work, show how the simultaneous consideration of a high [Mg/Fe] and a steep IMF slope would imply unreasonably short (tau~7 Myr) and intense (SFR~1e5 Msun/yr) formation events for massive early-type galaxies. Discuss possible caveats and explanations to this apparent inconsistency, and suggest that further IMF determinations, both in the local Universe and at high z, are necessary to better understand the problem.
1511.03391
Crowdsourcing quality control for Dark Energy Survey images
Melchior, Sheldon, et al
Developed a crowdsourcing web application for image quality control employed by DES. Dubbed the "DES exposure checker", it renders science-grade images directly to a web browser and allows users to mark problematic features from a set of predefined classes. Users can also generate custom labels and thus help identify previously unknown problem classes. User reports are fed back to hardware and software experts to help mitigate and eliminate recognized issues. Report on the implementation of the application and the experience with its over 100 users, the majority of which are professional or prospective astronomers but not data management experts. Discuss aspects of user training and engagement, and demonstrate how problem reports have been pivotal to rapidly correct artifacts which would likely have been too subtle or infrequent to be recognized otherwise. Conclude with a number of important lessons learned, suggest possible improvements, and recommend this collective exploratory approach for future astronomical surveys or wither extensive data sets wit a sufficiently large user base. Also release open-source code of the web application and host and online demo version.
1511.03594
The Gini Coefficient as a tool for image family identification in strong lensing systems with multiple images
Florian, Gladers, Li, Sharon
The sample of cosmo SL systems has been strongly growing in recent years; the sample will reach into the thousands with the advent of the next generation of space-based survey telescopes. The accuracy of SL models relies on robust ID of multiple image families of lensed galaxies. For the most massive lenses, often more than one background galaxy is magnified and multiply-imaged, and even in the cases of only a single lensed source, identification of counter images is not always robust. Recently, it was shown that the Gini coefficient in space-telescope-quality imaging is a measurement of galaxy morphology that is relatively well-preserved by strong gravitational lensing. Here, investigate its usefulness as a diagnostic for the purposes of image family identification and show that it can remove some of the degeneracies encountered when using color as the sole diagnostic, and can do so without the need for additional observations since whenever a color is available, two Gini coefficients are as well.
Tuesday, November 10, 2015
Day 1005
Wednesday.
1511.02854
Possible group origins VII. Galaxy substructures in fossil systems
Aarattani, et al
Fossil groups are expected to be the final product of galaxy merging within galaxy groups. In simulations, they are predicted to assemble their mass at high redshift. This early formation allows for the innermost M* galaxies to merge into a massive central galaxy. Then, they are expected to maintain their fossil status because of the few interactions within the LSS. In this context, the magnitude gap between the two brightness galaxies o f the system is considered a good indicator of its dynamical status. As a consequence, the systems with the largest gaps should be dynamically relaxed. In order to examine the dynamical status of these systems, systematically analyze the presence of galaxy substructures in a sample of 12 spectroscopically-confirmed fossil systems with 2d space of projected positions out to R200. Moreover, for a subsample of 5 systems with at least 30 spec-confirmed members, analyze the substructure in the velocity and in the 3-d velocity-position spaces. Additionally, look for signs of recent mergers in the regions around the central galaxies. Find that an important fraction of fossil systems show substructure. The fraction depends critically on the adopted test, since each test is more sensible to a particular type of substructure. The interpretation of the results is that fossil systems are not, in general, as relaxed as expected from simulations. The sample of 12 spec-confirmed fossils systems need to be extended in order to compute an accurate nation, but the conclusion is that this is similar to the fraction of substructure detected in non-fossil clusters.
1511.02862
Satellite quenching and galactic conformity at 0.3<z<2.5
Kawinwanichakij, et al
Measure the evolution of the quiescent fraction and quenching efficiency of satellites around SF and quiescent central galaxies with stellar mass log (Mcen/Msun)>10.5 at 0.3<z<2.5. combine imaging from 3 deep NIR selected surveys (ZFOURGE/CANDELS, UDS, and UltraVISTA), which allows us to select a stellar-mass complete sample of satellites with log (Msat/Msun)>9.3. Satellites for both SF and quiescent central galaxies have higher quiescent fractions compared to field galaxies matched in stellar mass at all redshifts. Also observe "galactic conformity": satellites around quiescent centrals are more likely to be quenched compared to the satellites around SF centrals. In the sample, this conformity signal is significant at >3 sigma for 0.6<z<1.6, whereas it is only weakly significant at 0.3<0.6 and 1.6<z<2.5 Therefore, conformity (and therefore satellite quenching) has been present for a significant fraction of the age of the universe. The satellite quenching efficiency increases with increasing stellar mass of the central, but does not appear to depend on the stellar mass of the satellite to the mass limit of the sample. When comparing the satellite quenching efficiency of SF centrals with stellar masses 0.2 dex higher than quiescent centrals (which should account for any difference in halo mass), the conformity signal decreases, but remains statistically significant at 0.6<z<0.9. This is evidence that satellite quenching is connected to the SF properties of the central as well as to the mass of the halo. Discuss physical effects that may contribute to galactic conformity, and emphasize that they must allow for continued SF in the central galaxy even as the satellites are quenched.
1511.02854
Possible group origins VII. Galaxy substructures in fossil systems
Aarattani, et al
Fossil groups are expected to be the final product of galaxy merging within galaxy groups. In simulations, they are predicted to assemble their mass at high redshift. This early formation allows for the innermost M* galaxies to merge into a massive central galaxy. Then, they are expected to maintain their fossil status because of the few interactions within the LSS. In this context, the magnitude gap between the two brightness galaxies o f the system is considered a good indicator of its dynamical status. As a consequence, the systems with the largest gaps should be dynamically relaxed. In order to examine the dynamical status of these systems, systematically analyze the presence of galaxy substructures in a sample of 12 spectroscopically-confirmed fossil systems with 2d space of projected positions out to R200. Moreover, for a subsample of 5 systems with at least 30 spec-confirmed members, analyze the substructure in the velocity and in the 3-d velocity-position spaces. Additionally, look for signs of recent mergers in the regions around the central galaxies. Find that an important fraction of fossil systems show substructure. The fraction depends critically on the adopted test, since each test is more sensible to a particular type of substructure. The interpretation of the results is that fossil systems are not, in general, as relaxed as expected from simulations. The sample of 12 spec-confirmed fossils systems need to be extended in order to compute an accurate nation, but the conclusion is that this is similar to the fraction of substructure detected in non-fossil clusters.
1511.02862
Satellite quenching and galactic conformity at 0.3<z<2.5
Kawinwanichakij, et al
Measure the evolution of the quiescent fraction and quenching efficiency of satellites around SF and quiescent central galaxies with stellar mass log (Mcen/Msun)>10.5 at 0.3<z<2.5. combine imaging from 3 deep NIR selected surveys (ZFOURGE/CANDELS, UDS, and UltraVISTA), which allows us to select a stellar-mass complete sample of satellites with log (Msat/Msun)>9.3. Satellites for both SF and quiescent central galaxies have higher quiescent fractions compared to field galaxies matched in stellar mass at all redshifts. Also observe "galactic conformity": satellites around quiescent centrals are more likely to be quenched compared to the satellites around SF centrals. In the sample, this conformity signal is significant at >3 sigma for 0.6<z<1.6, whereas it is only weakly significant at 0.3<0.6 and 1.6<z<2.5 Therefore, conformity (and therefore satellite quenching) has been present for a significant fraction of the age of the universe. The satellite quenching efficiency increases with increasing stellar mass of the central, but does not appear to depend on the stellar mass of the satellite to the mass limit of the sample. When comparing the satellite quenching efficiency of SF centrals with stellar masses 0.2 dex higher than quiescent centrals (which should account for any difference in halo mass), the conformity signal decreases, but remains statistically significant at 0.6<z<0.9. This is evidence that satellite quenching is connected to the SF properties of the central as well as to the mass of the halo. Discuss physical effects that may contribute to galactic conformity, and emphasize that they must allow for continued SF in the central galaxy even as the satellites are quenched.
Monday, November 9, 2015
Day 1004
Tuesday.
1511.02231
Towards a self-consistent halo model for the nonlinear large-scale structure
Schmidt
Halo model suffer from two major deficiencies: (i) they do not enforce the stress-energy conservation of matter; (ii) they are not guaranteed to recover exact perturbation theory results on large scales. Provide a formulation of the halo model ("EHM") that remedies both drawbacks in a consistent way, while attempting to maintain the productivity of the approach. In the formulation presented here, mass and momentum conservation are guaranteed, and results of perturbation theory and the effective field theory can in principle be matched to any desired order on large scales. Find that a key ingredient in the halo model PS is the halo stochasticity covariance, which has been studied to a much lesser extent than other ingredients such as MF, bias, and profiles of halos. As written here, this approach still does not describe the transition regime between perturbation theory and halo scales realistically, which is left as an open problem. Also show explicitly that, when implemented consistently, halo model predictions do not depend on any properties of low-mass haloes that are smaller than the scales of interest.
1511.02245
Galaxy and mass assembly (GAMA): growing up in a bad neighborhood - how do low-mass galaxies become passive?
Davies, et al
Both theoretical predictions and observations of the very nearby Universe suggest that low-mass galaxies (log10[M*/Msun]<9.5) are likely to remain SF unless they are affected by their local environment. To test this premise, compare and contrast the local environment of both passive and SF galaxies as a function of stellar mass, using GAMA. Find that passive fractions are higher in both interacting pair and group galaxies than the field at all stellar masses, and that this effect is most apparent in the lowest mass galaxies. Also find that essentially all passive log10[M*/Msun]<8.5 galaxies are found in pair/group environments, suggesting that local interactions with a more massive neighbor cause them to cease forming new stars. Find that the effects of immediate environment (local galaxy-galaxy interactions) in forming passive systems increases with decreasing stellar mass, and highlight that this is potentially due to increasing interaction timescales giving sufficient time for the galaxy to become passive via starvation. Present a simplistic model to test this premise, and show that given the speculative assumptions, it is consistent with the observed results.
1511.02363
Frequentist tests for Bayesian models
Lucy
Analogues of the frequentist chi-square and F tests are proposed for testing goodness-of-fit and consistency for Bayesian models. Simple examples exhibit these tests0' detection of inconsistency between consecutive experiments with identical parameters, when the first experiment provides the prior for the second. In a related analysis, a quantitative measure is derived for judging the degree of tension between two different experiments with partially overlapping parameter vectors.
1511.02549
Quantifying the origins of life on a planetary scale
Scharf, Cronin
A simple, heuristic formula with parallels to the Drake Equation is introduced to help focus discussion on open questions for the origins of file in a planetary context. This approach indicates a number of areas where quantitive progress can be made on parameter estimation for determining origins of life probabilities. Also suggest that the probability of origin of life events can be dramatically increased on planets with parallel chemistries that can undergo the development of complexity, and in solar systems where more than one planet is available for chemical evolution, and where efficient impact eject exchange occurs, increasing the effective chemical search space and available time.
1511.02231
Towards a self-consistent halo model for the nonlinear large-scale structure
Schmidt
Halo model suffer from two major deficiencies: (i) they do not enforce the stress-energy conservation of matter; (ii) they are not guaranteed to recover exact perturbation theory results on large scales. Provide a formulation of the halo model ("EHM") that remedies both drawbacks in a consistent way, while attempting to maintain the productivity of the approach. In the formulation presented here, mass and momentum conservation are guaranteed, and results of perturbation theory and the effective field theory can in principle be matched to any desired order on large scales. Find that a key ingredient in the halo model PS is the halo stochasticity covariance, which has been studied to a much lesser extent than other ingredients such as MF, bias, and profiles of halos. As written here, this approach still does not describe the transition regime between perturbation theory and halo scales realistically, which is left as an open problem. Also show explicitly that, when implemented consistently, halo model predictions do not depend on any properties of low-mass haloes that are smaller than the scales of interest.
1511.02245
Galaxy and mass assembly (GAMA): growing up in a bad neighborhood - how do low-mass galaxies become passive?
Davies, et al
Both theoretical predictions and observations of the very nearby Universe suggest that low-mass galaxies (log10[M*/Msun]<9.5) are likely to remain SF unless they are affected by their local environment. To test this premise, compare and contrast the local environment of both passive and SF galaxies as a function of stellar mass, using GAMA. Find that passive fractions are higher in both interacting pair and group galaxies than the field at all stellar masses, and that this effect is most apparent in the lowest mass galaxies. Also find that essentially all passive log10[M*/Msun]<8.5 galaxies are found in pair/group environments, suggesting that local interactions with a more massive neighbor cause them to cease forming new stars. Find that the effects of immediate environment (local galaxy-galaxy interactions) in forming passive systems increases with decreasing stellar mass, and highlight that this is potentially due to increasing interaction timescales giving sufficient time for the galaxy to become passive via starvation. Present a simplistic model to test this premise, and show that given the speculative assumptions, it is consistent with the observed results.
1511.02363
Frequentist tests for Bayesian models
Lucy
Analogues of the frequentist chi-square and F tests are proposed for testing goodness-of-fit and consistency for Bayesian models. Simple examples exhibit these tests0' detection of inconsistency between consecutive experiments with identical parameters, when the first experiment provides the prior for the second. In a related analysis, a quantitative measure is derived for judging the degree of tension between two different experiments with partially overlapping parameter vectors.
1511.02549
Quantifying the origins of life on a planetary scale
Scharf, Cronin
A simple, heuristic formula with parallels to the Drake Equation is introduced to help focus discussion on open questions for the origins of file in a planetary context. This approach indicates a number of areas where quantitive progress can be made on parameter estimation for determining origins of life probabilities. Also suggest that the probability of origin of life events can be dramatically increased on planets with parallel chemistries that can undergo the development of complexity, and in solar systems where more than one planet is available for chemical evolution, and where efficient impact eject exchange occurs, increasing the effective chemical search space and available time.
Sunday, November 8, 2015
Day 1003
Monday.
1511.01919
LoCuSS: testing hydrostatic equilibrium in galaxy clusters
Smith, et al
Test the assumption of hydrostatic equilibrium in an X-ray luminosity selected sample of 50 galaxy clusters at 0.15<z<0.3 from LoCuSS. The WL measurements of M500 control systematic biases to sub-4%, and the hydrostatic measurements of the same achieve excellent agreement between XMM-Newton and Chandra. The mean ratio of X-ray to lensing mass for these 50 clusters is beta_X=0.95±0.05, and for the 44 clusters also detected by Planck, the mean ratio of Planck mass estimate to LoCuSS lensing mass is beta_P=0.95±0.04. Based on a careful like-for-like analysis, find that LoCuSS, CCCP, and WtG agree on beta_P~0.9-0.95 at 0.15<z<0.3. This small level of hydrostatic bias disagrees at ~5sigma with the level required to reconcile planck cosmology results from the CMB and galaxy cluster counts.
1511.01983
The clustering and halo occupation distribution of Lyman-break galaxies at z~4
Park et al
Compare GALFORM SAM angular correlation function (ACF) of galaxies with XDF and CANDELS galaxies; find that the predicted ACFs are in good agreement with the measured ones, but the predicted ACFs show a weaker dependence on luminosity than is inferred from observations. Show act the fraction of satellite LBGs is important for determining the amplitude of the ACF on small scales. Find that central lyman-break galaxies (LBGs) at z~4 predominantly reside in haloes of mass 1e11-12 Msun/h and that satellites reside in larger haloes of mass 1e12-13 Msun/h. The model predicts fewer bright satellite LBGs at z~4 than are inferred from clustering measurements. Investigate the effect of the photometric scatter in the observations on the ACF predictions. Find the the observational uncertainty in the galaxy luminosity reduces the clustering amplitude, and that this effect increases toward faint galaxies, particularly on small scales. To compare properties of model LBGs with those of observations, this uncertainty must be considered. By analyzing the HOD, find evidence that AGN feedback affects the HOD of central LBGs in massive haloes.
1511.01919
LoCuSS: testing hydrostatic equilibrium in galaxy clusters
Smith, et al
Test the assumption of hydrostatic equilibrium in an X-ray luminosity selected sample of 50 galaxy clusters at 0.15<z<0.3 from LoCuSS. The WL measurements of M500 control systematic biases to sub-4%, and the hydrostatic measurements of the same achieve excellent agreement between XMM-Newton and Chandra. The mean ratio of X-ray to lensing mass for these 50 clusters is beta_X=0.95±0.05, and for the 44 clusters also detected by Planck, the mean ratio of Planck mass estimate to LoCuSS lensing mass is beta_P=0.95±0.04. Based on a careful like-for-like analysis, find that LoCuSS, CCCP, and WtG agree on beta_P~0.9-0.95 at 0.15<z<0.3. This small level of hydrostatic bias disagrees at ~5sigma with the level required to reconcile planck cosmology results from the CMB and galaxy cluster counts.
1511.01983
The clustering and halo occupation distribution of Lyman-break galaxies at z~4
Park et al
Compare GALFORM SAM angular correlation function (ACF) of galaxies with XDF and CANDELS galaxies; find that the predicted ACFs are in good agreement with the measured ones, but the predicted ACFs show a weaker dependence on luminosity than is inferred from observations. Show act the fraction of satellite LBGs is important for determining the amplitude of the ACF on small scales. Find that central lyman-break galaxies (LBGs) at z~4 predominantly reside in haloes of mass 1e11-12 Msun/h and that satellites reside in larger haloes of mass 1e12-13 Msun/h. The model predicts fewer bright satellite LBGs at z~4 than are inferred from clustering measurements. Investigate the effect of the photometric scatter in the observations on the ACF predictions. Find the the observational uncertainty in the galaxy luminosity reduces the clustering amplitude, and that this effect increases toward faint galaxies, particularly on small scales. To compare properties of model LBGs with those of observations, this uncertainty must be considered. By analyzing the HOD, find evidence that AGN feedback affects the HOD of central LBGs in massive haloes.
Friday, November 6, 2015
Day 1002
Friday.
1511.01484
How the first stars shaped the faintest gas-dominated dwarf galaxies
Verbeke, Vandenbroucke, De Rijcke
Low-mass dwarf galaxies are very sensitive test-beds for theories of cosmic structure formation since their weak gravitational fields allow the effects of the relevant physical processes to clearly stand out. Up to now, no unified account exists of the sometimes seemingly conflicting properties of the faintest isolated dwarfs in and around the Local Group, such as Leo T and the recently discovered Leo P and Pisces A systems. Using new numerical simulations, show that this serious challenge to the understanding of galaxy formation can be effectively resolved by taking into account the regulating influence of the UV radiation of the first population of stars on a dwarf's star formation rate while otherwise staying within the standard cosmo paradigm for structure formation. These simulations produce faint, gas-dominated, star-forming dwarf galaxies that lie on the baryonic Tully-Fisher relation and that successfully reproduce a broad range of chemical, kinematical, and structural observables of real late-type dwarf galaxies. Furthermore, stress the importance of obtaining properties of simulated galaxies in a manner as close as possible to the typically employed observational techniques.
1511.01484
How the first stars shaped the faintest gas-dominated dwarf galaxies
Verbeke, Vandenbroucke, De Rijcke
Low-mass dwarf galaxies are very sensitive test-beds for theories of cosmic structure formation since their weak gravitational fields allow the effects of the relevant physical processes to clearly stand out. Up to now, no unified account exists of the sometimes seemingly conflicting properties of the faintest isolated dwarfs in and around the Local Group, such as Leo T and the recently discovered Leo P and Pisces A systems. Using new numerical simulations, show that this serious challenge to the understanding of galaxy formation can be effectively resolved by taking into account the regulating influence of the UV radiation of the first population of stars on a dwarf's star formation rate while otherwise staying within the standard cosmo paradigm for structure formation. These simulations produce faint, gas-dominated, star-forming dwarf galaxies that lie on the baryonic Tully-Fisher relation and that successfully reproduce a broad range of chemical, kinematical, and structural observables of real late-type dwarf galaxies. Furthermore, stress the importance of obtaining properties of simulated galaxies in a manner as close as possible to the typically employed observational techniques.
Thursday, November 5, 2015
Day 1001
Wednesday.
1511.01096
Precision measurement of the local bias of dark matter halos
Lazeyras, Wagner, Baldauf, Schmidt
Present accurate measurements of the linear, quadratic, and cubic local bias of DM haloes, using curved "separate universe" N-body sims which effectively incorporate an infinite-wavelength overdensity. This can be seen as an exact implementation of the peak-background split argument. Compare the results with the linear and quadratic bias measured from the halo-matter power spectrum and bispectrum and find good agreement. On the other hand, the standard peak-background split applied to the Sheth+Tormen (1999) and TInker+(2008) halo mass functions matches the measured linear bias parameter only at the level of 10%. The prediction from the excursion set-peaks approach performs much better, which can be attributed to the stochastic moving barrier employed in the excursion set-peaks prediction. Also provide convenient fitting formulas for the nonlinear bias parameters b2(b1) and b3(b1).
1511.01097
Light versus dark in strong-lens galaxies: dark matter haloes that are rounder than their stars
Bruderer, et al
Measure the projected density profile, shape and alignment of the stellar and DM mass distribution in 11 SL galaxies. Find that the projected DM density profile - under the assumption of a Chabrier stellar IMF - shows significant variation from galaxy to galaxy. Those with an outermost image beyond ~10 kpc are very well fit by a projected NFW profile; those with images within 10 kpc appear to be more concentrated than NFW, as expected if their dark haloes contract due to baryonic cooling. Find that over several half-light radii, the DM haloes of these lenses are rounder than their stellar mass distributions. While the haloes are never more elliptical than e_dm=0.2, their stars can extend to e*>0.2. Galaxies with high DM ellipticity and weak external shear show strong alignment between light and dark; those with strong shear (gamma>0.1) can be highly misaligned. This is reassuring since isolated misaligned galaxies are expected to be unstable. The results provide a new constraint on galaxy formation models For a given cosmology, these must explain the origin of both very round DM haloes and misaligned strong-lens systems.
1511.01102
Improving Cosmological distance measurements using twin type Ia supernovae
Fakhouri, et al
A novel type of SNIa standardization. Begin with a well-measured set of SNe, find pairs whose spectra match well across the entire optical window, and then test whether this leads to a smaller dispersion in their absolute brightnesses. This analysis is completed in a blinded faschon, ensuring that decisions made in implementing the method do not inadvertently bias the result. Find that pairs of SNe with more closely matched spectra indeed have reduced brightness dispersion. Able to standardize this initial set of SNe to 0.083±0.012 mags, implying a dispersion of 0.072±0.010 magnitudes in the absence of peculiar velocities. Estimate that with larger number of comparison SNe, e.g., using the final SNFactory spectrophotometric dataset as a reference, this method will be capable of standardizing high-z supernovae to within 0.06±0.07 mags. These results imply that at least 3/4 of the variance in Hubble residuals in current supernova cosmology analyses is due to previously unaccounted-for astrophysics differences among the SNe.
1511.01352
Observational biases in flux magnification measurements
Hildebrandt
Flux magnification is an interesting complement to shear-based lensing measurements, especially at high z where sources are harder to resolve. One measures either changes in the source density (magnification bias) or in the shape of the flux distribution (e.g., magnitude-shift). The interpretation of these measurements relies on theoretical estimate of how the observables change under magnification. Present simulations to create multi-band photometric mock catalogues of Lyman-break galaxies in a CFHTLenS-like survey that include several observational effects that can change these relations, making simple theoretical estimates unusable. In particular, show how the magnification bias can be affected by photometric noise, color selection, and dust extinction. Find that a simple measurement of the slope of the number-counts is not sufficient for the precise interpretation of virtually all observations of magnification bias. Also explore how sensitive the shift in the mean magnitude of a source sample in different photometric bands is to magnification including the same observational effects. Again, find significant deviation from simple analytical estimates. Also discover a wavelength-dependence of the magnitude-shift effect when applied to a color-selected noise source sample. Such an effect can mimic the reddening by dust in the lens. It has to be disentangled from the dust extinction before the magnitude-shift/color-excess can be used to measure the distribution of either dark matter or extragalactic dust. Using simulations like the ones presented here these observational effects can be studied and eventually removed from observations making precise measurement of flux magnification possible.
1511.01465
Linear response to long wavelength fluctuations using curvature simulations
Baldauf, Seljak, Senatore, Zaldarriaga
Study the local response to long wavelength fluctuations in cosmo N-body sims, focusing on the matter and halo power spectra, haloes abundance and NL transformations of the density field. The long wavelength mode is implemented using an effective curved cosmology and a mapping of time and distances. The method provides an alternative, most probably more precise, way to measure the isotropic halo biases. Limiting to the linear case, find a generally good agreement between the biases obtained from the curvature method and the traditional power spectrum method at the level of a few precent. Also study the response of halo counts to changes in the variance of the field and find that the slope of the relation between the responses to density and variance differed form the naive derivation assuming a universal mass function by 18%. This has implications for measurements of the amplitude of local non-Gaussianity using scale dependent bias. Also analyze the halo PS and halo-DM cross-spectrum response to long wavelength fluctuations and derive second order halo bias from it, as well as the super-sample variance contribution to the galaxy PS covariance matrix.
1511.01096
Precision measurement of the local bias of dark matter halos
Lazeyras, Wagner, Baldauf, Schmidt
Present accurate measurements of the linear, quadratic, and cubic local bias of DM haloes, using curved "separate universe" N-body sims which effectively incorporate an infinite-wavelength overdensity. This can be seen as an exact implementation of the peak-background split argument. Compare the results with the linear and quadratic bias measured from the halo-matter power spectrum and bispectrum and find good agreement. On the other hand, the standard peak-background split applied to the Sheth+Tormen (1999) and TInker+(2008) halo mass functions matches the measured linear bias parameter only at the level of 10%. The prediction from the excursion set-peaks approach performs much better, which can be attributed to the stochastic moving barrier employed in the excursion set-peaks prediction. Also provide convenient fitting formulas for the nonlinear bias parameters b2(b1) and b3(b1).
1511.01097
Light versus dark in strong-lens galaxies: dark matter haloes that are rounder than their stars
Bruderer, et al
Measure the projected density profile, shape and alignment of the stellar and DM mass distribution in 11 SL galaxies. Find that the projected DM density profile - under the assumption of a Chabrier stellar IMF - shows significant variation from galaxy to galaxy. Those with an outermost image beyond ~10 kpc are very well fit by a projected NFW profile; those with images within 10 kpc appear to be more concentrated than NFW, as expected if their dark haloes contract due to baryonic cooling. Find that over several half-light radii, the DM haloes of these lenses are rounder than their stellar mass distributions. While the haloes are never more elliptical than e_dm=0.2, their stars can extend to e*>0.2. Galaxies with high DM ellipticity and weak external shear show strong alignment between light and dark; those with strong shear (gamma>0.1) can be highly misaligned. This is reassuring since isolated misaligned galaxies are expected to be unstable. The results provide a new constraint on galaxy formation models For a given cosmology, these must explain the origin of both very round DM haloes and misaligned strong-lens systems.
1511.01102
Improving Cosmological distance measurements using twin type Ia supernovae
Fakhouri, et al
A novel type of SNIa standardization. Begin with a well-measured set of SNe, find pairs whose spectra match well across the entire optical window, and then test whether this leads to a smaller dispersion in their absolute brightnesses. This analysis is completed in a blinded faschon, ensuring that decisions made in implementing the method do not inadvertently bias the result. Find that pairs of SNe with more closely matched spectra indeed have reduced brightness dispersion. Able to standardize this initial set of SNe to 0.083±0.012 mags, implying a dispersion of 0.072±0.010 magnitudes in the absence of peculiar velocities. Estimate that with larger number of comparison SNe, e.g., using the final SNFactory spectrophotometric dataset as a reference, this method will be capable of standardizing high-z supernovae to within 0.06±0.07 mags. These results imply that at least 3/4 of the variance in Hubble residuals in current supernova cosmology analyses is due to previously unaccounted-for astrophysics differences among the SNe.
1511.01352
Observational biases in flux magnification measurements
Hildebrandt
Flux magnification is an interesting complement to shear-based lensing measurements, especially at high z where sources are harder to resolve. One measures either changes in the source density (magnification bias) or in the shape of the flux distribution (e.g., magnitude-shift). The interpretation of these measurements relies on theoretical estimate of how the observables change under magnification. Present simulations to create multi-band photometric mock catalogues of Lyman-break galaxies in a CFHTLenS-like survey that include several observational effects that can change these relations, making simple theoretical estimates unusable. In particular, show how the magnification bias can be affected by photometric noise, color selection, and dust extinction. Find that a simple measurement of the slope of the number-counts is not sufficient for the precise interpretation of virtually all observations of magnification bias. Also explore how sensitive the shift in the mean magnitude of a source sample in different photometric bands is to magnification including the same observational effects. Again, find significant deviation from simple analytical estimates. Also discover a wavelength-dependence of the magnitude-shift effect when applied to a color-selected noise source sample. Such an effect can mimic the reddening by dust in the lens. It has to be disentangled from the dust extinction before the magnitude-shift/color-excess can be used to measure the distribution of either dark matter or extragalactic dust. Using simulations like the ones presented here these observational effects can be studied and eventually removed from observations making precise measurement of flux magnification possible.
1511.01465
Linear response to long wavelength fluctuations using curvature simulations
Baldauf, Seljak, Senatore, Zaldarriaga
Study the local response to long wavelength fluctuations in cosmo N-body sims, focusing on the matter and halo power spectra, haloes abundance and NL transformations of the density field. The long wavelength mode is implemented using an effective curved cosmology and a mapping of time and distances. The method provides an alternative, most probably more precise, way to measure the isotropic halo biases. Limiting to the linear case, find a generally good agreement between the biases obtained from the curvature method and the traditional power spectrum method at the level of a few precent. Also study the response of halo counts to changes in the variance of the field and find that the slope of the relation between the responses to density and variance differed form the naive derivation assuming a universal mass function by 18%. This has implications for measurements of the amplitude of local non-Gaussianity using scale dependent bias. Also analyze the halo PS and halo-DM cross-spectrum response to long wavelength fluctuations and derive second order halo bias from it, as well as the super-sample variance contribution to the galaxy PS covariance matrix.
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