95 research outputs found
How are galaxies assigned to halos? Searching for assembly bias in the SDSS galaxy clustering
Clustering of dark matter halos has been shown to depend on halo properties
beyond mass such as halo concentration, a phenomenon referred to as halo
assembly bias. Standard halo occupation models (HOD) in large scale structure
studies assume that halo mass alone is sufficient in characterizing the
connection between galaxies and halos. Modeling of galaxy clustering can face
systematic effects if the number of galaxies within a halo is correlated with
other halo properties. Using the Small MultiDark-Planck high resolution
-body simulation and the clustering measurements of the Sloan Digital Sky
Survey (SDSS) DR7 main galaxy sample, we investigate the extent to which the
concentration-dependence of halo occupation can be constrained. Furthermore, we
study how allowing for the concentration dependence can improve our modeling of
galaxy clustering.
Our constraints on HOD with assembly bias suggest that satellite population
is not correlated with halo concentration at fixed halo mass. At fixed halo
mass, our constraints favor lack of correlation between the occupation of
centrals and halo concentration in the most luminous samples (), and modest correlation in the
samples. We show that in comparison with abundance-matching mock catalogs, our
findings suggest qualitatively similar but modest levels of the impact of halo
assembly bias on galaxy clustering. The effect is only present in the central
occupation and becomes less significant in brighter galaxy samples.
Furthermore, by performing model comparison based on information criteria, we
find that in most cases, the standard mass-only HOD model is still favored by
the observations.Comment: Accepted for publication in Ap
Star Formation Quenching Timescale of Central Galaxies in a Hierarchical Universe
Central galaxies make up the majority of the galaxy population, including the
majority of the quiescent population at . Thus, the mechanism(s) responsible for quenching
central galaxies plays a crucial role in galaxy evolution as whole. We combine
a high resolution cosmological -body simulation with observed evolutionary
trends of the "star formation main sequence," quiescent fraction, and stellar
mass function at to construct a model that statistically tracks the
star formation histories and quenching of central galaxies. Comparing this
model to the distribution of central galaxy star formation rates in a group
catalog of the SDSS Data Release 7, we constrain the timescales over which
physical processes cease star formation in central galaxies. Over the stellar
mass range to we infer quenching
e-folding times that span to with more massive
central galaxies quenching faster. For , this implies a total migration time of from the star formation main sequence to quiescence. Compared
to satellites, central galaxies take longer to quench
their star formation, suggesting that different mechanisms are responsible for
quenching centrals versus satellites. Finally, the central galaxy quenching
timescale we infer provides key constraints for proposed star formation
quenching mechanisms. Our timescale is generally consistent with gas depletion
timescales predicted by quenching through strangulation. However, the exact
physical mechanism(s) responsible for this still remain unclear.Comment: 16 pages, 11 figure
Likelihood Non-Gaussianity in Large-Scale Structure Analyses
Standard present day large-scale structure (LSS) analyses make a major
assumption in their Bayesian parameter inference --- that the likelihood has a
Gaussian form. For summary statistics currently used in LSS, this assumption,
even if the underlying density field is Gaussian, cannot be correct in detail.
We investigate the impact of this assumption on two recent LSS analyses: the
Beutler et al. (2017) power spectrum multipole () analysis and the
Sinha et al. (2017) group multiplicity function () analysis. Using
non-parametric divergence estimators on mock catalogs originally constructed
for covariance matrix estimation, we identify significant non-Gaussianity in
both the and likelihoods. We then use Gaussian mixture density
estimation and Independent Component Analysis on the same mocks to construct
likelihood estimates that approximate the true likelihood better than the
Gaussian -likelihood. Using these likelihood estimates, we accurately
estimate the true posterior probability distribution of the Beutler et al.
(2017) and Sinha et al. (2017) parameters. Likelihood non-Gaussianity shifts
the constraint by , but otherwise, does not
significantly impact the overall parameter constraints of Beutler et al.
(2017). For the analysis, using the pseudo-likelihood significantly
underestimates the uncertainties and biases the constraints of Sinha et al.
(2017) halo occupation parameters. For and , the posteriors
are shifted by and and broadened by and
, respectively. The divergence and likelihood estimation methods we
present provide a straightforward framework for quantifying the impact of
likelihood non-Gaussianity and deriving more accurate parameter constraints.Comment: 33 pages, 7 figure
Neural Stellar Population Synthesis Emulator for the DESI PROVABGS
The Probabilistic Value-Added Bright Galaxy Survey (PROVABGS) catalog will
provide the posterior distributions of physical properties of million
DESI Bright Galaxy Survey (BGS) galaxies. Each posterior distribution will be
inferred from joint Bayesian modeling of observed photometry and spectroscopy
using Markov Chain Monte Carlo sampling and the [arXiv:2202.01809] stellar
population synthesis (SPS) model. To make this computationally feasible,
PROVABGS will use a neural emulator for the SPS model to accelerate the
posterior inference. In this work, we present how we construct the emulator
using the [arXiv:1911.11778] approach and verify that it can be used to
accurately infer galaxy properties. We confirm that the emulator is in
excellent agreement with the original SPS model with error and is
faster. In addition, we demonstrate that the posteriors of galaxy
properties derived using the emulator are also in excellent agreement with
those inferred using the original model. The neural emulator presented in this
work is essential in bypassing the computational challenge posed in
constructing the PROVABGS catalog. Furthermore, it demonstrates the advantages
of emulation for scaling sophisticated analyses to millions of galaxies.Comment: 9 pages, 5 figures, submitted to ApJ
Cosmology with Galaxy Photometry Alone
We present the first cosmological constraints using only the observed
photometry of galaxies. Villaescusa-Navarro et al. (2022; arXiv:2201.02202)
recently demonstrated that the internal physical properties of a single
simulated galaxy contain a significant amount of cosmological information.
These physical properties, however, cannot be directly measured from
observations. In this work, we present how we can go beyond theoretical
demonstrations to infer cosmological constraints from actual galaxy observables
(e.g. optical photometry) using neural density estimation and the CAMELS suite
of hydrodynamical simulations. We find that the cosmological information in the
photometry of a single galaxy is limited. However, we combine the constraining
power of photometry from many galaxies using hierarchical population inference
and place significant cosmological constraints. With the observed photometry of
20,000 NASA-Sloan Atlas galaxies, we constrain and .Comment: 15 pages, 7 figures, submitted to ApJL, comments welcom
Cosmological Information in Skew Spectra of Biased Tracers in Redshift Space
Extracting the non-Gaussian information encoded in the higher-order
clustering statistics of the large-scale structure is key to fully realizing
the potential of upcoming galaxy surveys. We investigate the information
content of the redshift-space {\it weighted skew spectra} of biased tracers as
efficient estimators for 3-point clustering statistics. The skew spectra are
constructed by correlating the observed galaxy field with an
appropriately-weighted square of it. We perform numerical Fisher forecasts
using two synthetic datasets; the halo catalogs from the Quijote N-body
simulations and the galaxy catalogs from the Molino suite. The latter serves to
understand the effect of marginalization over a more complex matter-tracer
biasing relation. Compared to the power spectrum multipoles, we show that the
skew spectra substantially improve the constraints on six parameters of the
CDM model, .
Imposing a small-scale cutoff of , the
improvements from skew spectra alone range from 23% to 62% for the Quijote
halos and from 32% to 71% for the Molino galaxies. Compared to the previous
analysis of the bispectrum monopole on the same data and using the same range
of scales, the skew spectra of Quijote halos provide competitive constraints.
Conversely, the skew spectra outperform the bispectrum monopole for all
cosmological parameters for the Molino catalogs. This may result from
additional anisotropic information, particularly enhanced in the Molino sample,
that is captured by the skew spectra but not by the bispectrum monopole. Our
stability analysis of the numerical derivatives shows comparable convergence
rates for the power spectrum and the skew spectra, indicating potential
underestimation of parameter uncertainties by at most 30%.Comment: 43 pages, 25 figure
Differentiable Stochastic Halo Occupation Distribution
In this work, we demonstrate how differentiable stochastic sampling
techniques developed in the context of deep Reinforcement Learning can be used
to perform efficient parameter inference over stochastic, simulation-based,
forward models. As a particular example, we focus on the problem of estimating
parameters of Halo Occupancy Distribution (HOD) models which are used to
connect galaxies with their dark matter halos. Using a combination of
continuous relaxation and gradient parameterization techniques, we can obtain
well-defined gradients with respect to HOD parameters through discrete galaxy
catalogs realizations. Having access to these gradients allows us to leverage
efficient sampling schemes, such as Hamiltonian Monte-Carlo, and greatly speed
up parameter inference. We demonstrate our technique on a mock galaxy catalog
generated from the Bolshoi simulation using the Zheng et al. 2007 HOD model and
find near identical posteriors as standard Markov Chain Monte Carlo techniques
with an increase of ~8x in convergence efficiency. Our differentiable HOD model
also has broad applications in full forward model approaches to cosmic
structure and cosmological analysis.Comment: 10 pages, 6 figures, comments welcom
Halo histories versus galaxy properties at z = 0 β III. The properties of star-forming galaxies
We measure how the properties of star-forming central galaxies correlate with large-scale environment, Ξ΄, measured on 10 h^(β1)βMpc scales. We use galaxy group catalogues to isolate a robust sample of central galaxies with high purity and completeness. The galaxy properties we investigate are star formation rate (SFR), exponential disc scale length R_(exp), and Sersic index of the galaxy light profile, n_S. We find that, at all stellar masses, there is an inverse correlation between SFR and Ξ΄, meaning that above-average star-forming centrals live in underdense regions. For n_S and R_(exp), there is no correlation with Ξ΄ at M* β² 10^(10.5)Mβ, but at higher masses there are positive correlations; a weak correlation with R_(exp) and a strong correlation with n_S. These data are evidence of assembly bias within the star-forming population. The results for SFR are consistent with a model in which SFR correlates with present-day halo accretion rate, M_h. In this model, galaxies are assigned to haloes using the abundance-matching ansatz, which maps galaxy stellar mass onto halo mass. At fixed halo mass, SFR is then assigned to galaxies using the same approach, but
M_h is used to map onto SFR. The best-fitting model requires some scatter in the M_h
βSFR relation. The R_(exp) and n_S measurements are consistent with a model in which both of these quantities are correlated with the spin parameter of the halo, Ξ». Halo spin does not correlate with Ξ΄ at low halo masses, but for higher mass haloes, high-spin haloes live in higher density environments at fixed M_h. Put together with the earlier instalments of this series, these data demonstrate that quenching processes have limited correlation with halo formation history, but the growth of active galaxies, as well as other detailed galaxies properties, are influenced by the details of halo assembly
- β¦