256 research outputs found
A Simple Technique for Predicting High-Redshift Galaxy Evolution
We show that the ratio of galaxies' specific star formation rates (SSFRs) to
their host halos' specific mass accretion rates (SMARs) strongly constrains how
the galaxies' stellar masses, specific star formation rates, and host halo
masses evolve over cosmic time. This evolutionary constraint provides a simple
way to probe z>8 galaxy populations without direct observations. Tests of the
method with galaxy properties at z=4 successfully reproduce the known evolution
of the stellar mass--halo mass (SMHM) relation, galaxy SSFRs, and the cosmic
star formation rate (CSFR) for 5<z<8. We then predict the continued evolution
of these properties for 8<z<15. In contrast to the non-evolution in the SMHM
relation at z<4, the median galaxy mass at fixed halo mass increases strongly
at z>4. We show that this result is closely linked to the flattening in galaxy
SSFRs at z>2 compared to halo specific mass accretion rates; we expect that
average galaxy SSFRs at fixed stellar mass will continue their mild evolution
to z~15. The expected CSFR shows no breaks or features at z>8.5; this
constrains both reionization and the possibility of a steep falloff in the CSFR
at z=9-10. Finally, we make predictions for stellar mass and luminosity
functions for the James Webb Space Telescope (JWST), which should be able to
observe one galaxy with M* > ~10^8 Msun per 10^3 Mpc^3 at z=9.6 and one such
galaxy per 10^4 Mpc^3 at z=15.Comment: Revised to include JWST luminosity functions, matching accepted
versio
Emission from the Ionized Gaseous Halos of Low Redshift Galaxies and Their Neighbors
Using a sample of nearly half a million galaxies, intersected by over 8
million lines of sight from the Sloan Digital Sky Survey Data Release 12, we
extend our previous study of the recombination radiation emitted by the gaseous
halos of nearby galaxies. We identify an inflection in the radial profile of
the H+N[{\small II}] radial emission profile at a projected radius of
kpc and suggest that beyond this radius the emission from ionized gas
in spatially correlated halos dominates the profile. We confirm that this is a
viable hypothesis using results from a highly simplified theoretical treatment
in which the dark matter halo distribution from cosmological simulations is
straightforwardly populated with gas. Whether we fit the fraction of halo gas
in a cooler (T K), smooth () component (0.26 for galaxies
with M M and 0.34 for those with M
M) or take independent values of this fraction from published
hydrodynamical simulations (0.19 and 0.38, respectively), this model
successfully reproduces the radial location and amplitude of the observed
inflection. We also observe that the physical nature of the gaseous halo
connects to primary galaxy morphology beyond any relationship to the galaxy's
stellar mass and star formation rate. We explore whether the model reproduces
behavior related to the central galaxy's stellar mass, star formation rate, and
morphology. We find that it is unsuccessful in reproducing the observations at
this level of detail and discuss various shortcomings of our simple model that
may be responsible.Comment: 10 pages, 8 figures, accepted by Ap
Constraining Scatter in the Stellar Mass--Halo Mass Relation for Haloes Less Massive than the Milky Way
Most galaxies are hosted by massive, invisible dark matter haloes, yet little
is known about the scatter in the stellar mass--halo mass relation for galaxies
with host halo masses . Using mock catalogues based
on dark matter simulations, we find that two observable signatures are
sensitive to scatter in the stellar mass--halo mass relation even at these mass
scales; i.e., conditional stellar mass functions and velocity distribution
functions for neighbouring galaxies. We compute these observables for 179,373
galaxies in the Sloan Digital Sky Survey (SDSS) with stellar masses and redshifts 0.01 0.307. We then compare to mock
observations generated from the dark matter
simulation for stellar mass--halo mass scatters ranging from 0 to 0.6 dex. The
observed results are consistent with simulated results for most values of
scatter (0.6 dex), and SDSS statistics are insufficient to provide firm
constraints. However, this method could provide much tighter constraints on
stellar mass--halo mass scatter in the future if applied to larger data sets,
especially the anticipated Dark Energy Spectroscopic Instrument Bright Galaxy
Survey. Constraining the value of scatter could have important implications for
galaxy formation and evolution.Comment: 11 pages, 1 table, 9 main body figures, 9 appendix figure
A Comprehensive Analysis of Uncertainties Affecting the Stellar Mass - Halo Mass Relation for 0<z<4
We conduct a comprehensive analysis of the relationship between central
galaxies and their host dark matter halos, as characterized by the stellar
mass-halo mass (SM-HM) relation, with rigorous consideration of uncertainties.
Our analysis focuses on results from the abundance matching technique, which
assumes that every dark matter halo or subhalo above a specific mass threshold
hosts one galaxy. We discuss the quantitative effects of uncertainties in
observed galaxy stellar mass functions (GSMFs) (including stellar mass
estimates and counting uncertainties), halo mass functions (including cosmology
and uncertainties from substructure), and the abundance matching technique used
to link galaxies to halos (including scatter in this connection). Our analysis
results in a robust estimate of the SM-HM relation and its evolution from z=0
to z=4. The shape and evolution are well constrained for z < 1. The largest
uncertainties at these redshifts are due to stellar mass estimates; however,
failure to account for scatter in stellar masses at fixed halo mass can lead to
errors of similar magnitude in the SM-HM relation for central galaxies in
massive halos. We also investigate the SM-HM relation to z=4, although the
shape of the relation at higher redshifts remains fairly unconstrained when
uncertainties are taken into account. These results will provide a powerful
tool to inform galaxy evolution models. [Abridged]Comment: 27 pages, 12 figures, updated to match ApJ accepted version
Clustering Constraints on the Relative Sizes of Central and Satellite Galaxies
We empirically constrain how galaxy size relates to halo virial radius using
new measurements of the size- and stellar mass-dependent clustering of galaxies
in the Sloan Digital Sky Survey. We find that small galaxies cluster much more
strongly than large galaxies of the same stellar mass. The magnitude of this
clustering difference increases on small scales, and decreases with increasing
stellar mass. Using Halotools to forward model the observations, we test an
empirical model in which present-day galaxy size is proportional to the size of
the virial radius at the time the halo reached its maximum mass. This simple
model reproduces the observed size-dependence of galaxy clustering in striking
detail. The success of this model provides strong support for the conclusion
that satellite galaxies have smaller sizes relative to central galaxies of the
same halo mass. Our findings indicate that satellite size is set prior to the
time of infall, and that a remarkably simple, linear size--virial radius
relation emerges from the complex physics regulating galaxy size. We make
quantitative predictions for future measurements of galaxy-galaxy lensing,
including dependence upon size, scale, and stellar mass, and provide a scaling
relation of the ratio of mean sizes of satellites and central galaxies as a
function of their halo mass that can be used to calibrate hydrodynamical
simulations and semi-analytic models.Comment: 12 pages plus an appendix. Submitted to MNRAS. Figure 5 shows that a
simple empirical model, with R50 = 0.01Rvir, can accurately reproduce new
measurements of size-dependent clustering of SDSS galaxies. Figure 9 shows
predictions for the size-dependence of future lensing measurements. Figure 10
provides a diagnostic for hydro sims and SAM
Emission line ratios for the Circumgalactic Medium and the "Bimodal" Nature of Galaxies
We find significantly different diagnostic emission line ratios for the
circumgalactic gas associated with galaxies of stellar masses above and below
M using SDSS spectroscopy. Specifically, in a sample of
17,393 galaxies, intersected by 18,535 lines of sight at projected radii
between 10 and 50 kpc, we stack measured fluxes for nebular strong emission
lines, [O {\small III}] 5007, H and [N {\small II}]
, and find that the gas surrounding the lower mass galaxies
exhibits similar line ratios to those of gas ionized by star formation and that
surrounding the higher mass galaxies similar to those of gas ionized by AGN or
shocks. This finding highlights yet another characteristic of galaxies that is
distinctly different above and below this stellar mass threshold, but one that
is more closely connected to the gas accretion behavior hypothesized to be
responsible for this dichotomy.Comment: 5 pages, 3 figures, accepted by ApJ
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