137 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
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
The Rockstar Phase-Space Temporal Halo Finder and the Velocity Offsets of Cluster Cores
We present a new algorithm for identifying dark matter halos, substructure,
and tidal features. The approach is based on adaptive hierarchical refinement
of friends-of-friends groups in six phase-space dimensions and one time
dimension, which allows for robust (grid-independent, shape-independent, and
noise-resilient) tracking of substructure; as such, it is named Rockstar
(Robust Overdensity Calculation using K-Space Topologically Adaptive
Refinement). Our method is massively parallel (up to 10^5 CPUs) and runs on the
largest current simulations (>10^10 particles) with high efficiency (10 CPU
hours and 60 gigabytes of memory required per billion particles analyzed). A
previous paper (Knebe et al 2011) has shown Rockstar to have class-leading
recovery of halo properties; we expand on these comparisons with more tests and
higher-resolution simulations. We show a significant improvement in
substructure recovery as compared to several other halo finders and discuss the
theoretical and practical limits of simulations in this regard. Finally, we
present results which demonstrate conclusively that dark matter halo cores are
not at rest relative to the halo bulk or satellite average velocities and have
coherent velocity offsets across a wide range of halo masses and redshifts. For
massive clusters, these offsets can be up to 350 km/s at z=0 and even higher at
high redshifts. Our implementation is publicly available at
http://code.google.com/p/rockstar .Comment: 20 pages, 14 figures. Minor revisions to match accepted versio
The bias of the submillimetre galaxy population: SMGs are poor tracers of the most massive structures in the z ~ 2 Universe
It is often claimed that overdensities of (or even individual bright)
submillimetre-selected galaxies (SMGs) trace the assembly of the most-massive
dark matter structures in the Universe. We test this claim by performing a
counts-in-cells analysis of mock SMG catalogues derived from the Bolshoi
cosmological simulation to investigate how well SMG associations trace the
underlying dark matter structure. We find that SMGs exhibit a relatively
complex bias: some regions of high SMG overdensity are underdense in terms of
dark matter mass, and some regions of high dark matter overdensity contain no
SMGs. Because of their rarity, Poisson noise causes scatter in the SMG
overdensity at fixed dark matter overdensity. Consequently, rich associations
of less-luminous, more-abundant galaxies (i.e. Lyman-break galaxy analogues)
trace the highest dark matter overdensities much better than SMGs. Even on
average, SMG associations are relatively poor tracers of the most significant
dark matter overdensities because of 'downsizing': at z < ~2.5, the
most-massive galaxies that reside in the highest dark matter overdensities have
already had their star formation quenched and are thus no longer SMGs. At a
given redshift, of the 10 per cent most-massive overdensities, only ~25 per
cent contain at least one SMG, and less than a few per cent contain more than
one SMG.Comment: 6 pages, 3 figures, 1 table; accepted for publication in MNRAS; minor
revisions from previous version, conclusions unchange
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