643 research outputs found
Evolution of the atomic and molecular gas content of galaxies in dark matter haloes
We present a semi-empirical model to infer the atomic and molecular hydrogen
content of galaxies as a function of halo mass and time. Our model combines the
SFR-halo mass-redshift relation (constrained by galaxy abundances) with
inverted SFR-surface density relations to infer galaxy H I and H2 masses. We
present gas scaling relations, gas fractions, and mass functions from z = 0 to
z = 3 and the gas properties of galaxies as a function of their host halo
masses. Predictions of our work include: 1) there is a ~ 0.2 dex decrease in
the H I mass of galaxies as a function of their stellar mass since z = 1.5,
whereas the H2 mass of galaxies decreases by > 1 dex over the same period. 2)
galaxy cold gas fractions and H2 fractions decrease with increasing stellar
mass and time. Galaxies with M* > 10^10 Msun are dominated by their stellar
content at z < 1, whereas less-massive galaxies only reach these gas fractions
at z = 0. We find the strongest evolution in relative gas content at z < 1.5.
3) the SFR to gas mass ratio decreases by an order of magnitude from z = 3 to z
= 0. This is consistent with lower H2 fractions; these lower fractions in
combination with smaller gas reservoirs correspond to decreased present-day
galaxy SFRs. 4) an H2-based star- formation relation can simultaneously fuel
the evolution of the cosmic star-formation and reproduce the observed weak
evolution in the cosmic HI density. 5) galaxies residing in haloes with masses
near 10^12 Msun are most efficient at obtaining large gas reservoirs and
forming H2 at all redshifts. These two effects lie at the origin of the high
star-formation efficiencies in haloes with the same mass.Comment: accepted for publication in MNRAS, 20 pages, 16 figures (+ 1 figure
in appendix), data files are accessible through
http://www.eso.org/~gpopping/Gergo_Poppings_Homepage/Data.htm
Connecting massive galaxies to dark matter halos in BOSS - I. Is galaxy color a stochastic process in high-mass halos?
We use subhalo abundance matching (SHAM) to model the stellar mass function
(SMF) and clustering of the Baryon Oscillation Spectroscopic Survey (BOSS)
"CMASS" sample at . We introduce a novel method which accounts for
the stellar mass incompleteness of CMASS as a function of redshift, and produce
CMASS mock catalogs which include selection effects, reproduce the overall SMF,
the projected two-point correlation function , the CMASS ,
and are made publicly available. We study the effects of assembly bias above
collapse mass in the context of "age matching" and show that these effects are
markedly different compared to the ones explored by Hearin et al. (2013) at
lower stellar masses. We construct two models, one in which galaxy color is
stochastic ("AbM" model) as well as a model which contains assembly bias
effects ("AgM" model). By confronting the redshift dependent clustering of
CMASS with the predictions from our model, we argue that that galaxy colors are
not a stochastic process in high-mass halos. Our results suggest that the
colors of galaxies in high-mass halos are determined by other halo properties
besides halo peak velocity and that assembly bias effects play an important
role in determining the clustering properties of this sample.Comment: 22 pages. Appendix. B added. Matches the version accepted by MNRAS.
Mock galaxy catalog and HOD table are available at
http://www.massivegalaxies.co
Conformally invariant wave-equations and massless fields in de Sitter spacetime
Conformally invariant wave equations in de Sitter space, for scalar and
vector fields, are introduced in the present paper. Solutions of their wave
equations and the related two-point functions, in the ambient space notation,
have been calculated. The ``Hilbert'' space structure and the field operator,
in terms of coordinate independent de Sitter plane waves, have been defined.
The construction of the paper is based on the analyticity in the complexified
pseudo-Riemanian manifold, presented first by Bros et al.. Minkowskian limits
of these functions are analyzed. The relation between the ambient space
notation and the intrinsic coordinates is then studied in the final stage.Comment: 21 pages, LaTeX, some details adde
Evolution of the Stellar-to-Dark Matter relation: separating star-forming and passive galaxies from z = 1 to 0
We use measurements of the stellar mass function, galaxy clustering, and galaxy-galaxy lensing within the COSMOS survey to constrain the stellar-to-halo mass relation (SHMR) of star forming and quiescent galaxies over the redshift range z = [0.2, 1.0]. For massive galaxies, M * gsim 1010.6 M ☉, our results indicate that star-forming galaxies grow proportionately as fast as their dark matter halos while quiescent galaxies are outpaced by dark matter growth. At lower masses, there is minimal difference in the SHMRs, implying that the majority low-mass quiescent galaxies have only recently been quenched of their star formation. Our analysis also affords a breakdown of all COSMOS galaxies into the relative numbers of central and satellite galaxies for both populations. At z = 1, satellite galaxies dominate the red sequence below the knee in the stellar mass function. But the number of quiescent satellites exhibits minimal redshift evolution; all evolution in the red sequence is due to low-mass central galaxies being quenched of their star formation. At M * ~ 1010 M ☉, the fraction of central galaxies on the red sequence increases by a factor of 10 over our redshift baseline, while the fraction of quenched satellite galaxies at that mass is constant with redshift. We define a "migration rate" to the red sequence as the time derivative of the passive galaxy abundances. We find that the migration rate of central galaxies to the red sequence increases by nearly an order of magnitude from z = 1 to z = 0. These results imply that the efficiency of quenching star formation for centrals is increasing with cosmic time, while the mechanisms that quench the star formation of satellite galaxies in groups and clusters is losing efficiency
An Increasing Stellar Baryon Fraction in Bright Galaxies at High Redshift
Recent observations have shown that the characteristic luminosity of the
rest-frame ultraviolet (UV) luminosity function does not significantly evolve
at 4 < z < 7 and is approximately M*_UV ~ -21. We investigate this apparent
non-evolution by examining a sample of 178 bright, M_UV < -21 galaxies at z=4
to 7, analyzing their stellar populations and host halo masses. Including deep
Spitzer/IRAC imaging to constrain the rest-frame optical light, we find that
M*_UV galaxies at z=4-7 have similar stellar masses of log(M/Msol)=9.6-9.9 and
are thus relatively massive for these high redshifts. However, bright galaxies
at z=4-7 are less massive and have younger inferred ages than similarly bright
galaxies at z=2-3, even though the two populations have similar star formation
rates and levels of dust attenuation. We match the abundances of these bright
z=4-7 galaxies to halo mass functions from the Bolshoi Lambda-CDM simulation to
estimate the halo masses. We find that the typical halo masses in ~M*_UV
galaxies decrease from log(M_h/Msol)=11.9 at z=4 to log(M_h/Msol)=11.4 at z=7.
Thus, although we are studying galaxies at a similar mass across multiple
redshifts, these galaxies live in lower mass halos at higher redshift. The
stellar baryon fraction in units of the cosmic mean Omega_b/Omega_m rises from
5.1% at z=4 to 11.7% at z=7; this evolution is significant at the ~3-sigma
level. This rise does not agree with simple expectations of how galaxies grow,
and implies that some effect, perhaps a diminishing efficiency of feedback, is
allowing a higher fraction of available baryons to be converted into stars at
high redshifts.Comment: Accepted to ApJ. 15 pages, 5 figures, 6 table
An Empirical Mass Function Distribution
The halo mass function, encoding the comoving number density of dark matter halos of a given mass, plays a key role in understanding the formation and evolution of galaxies. As such, it is a key goal of current and future deep optical surveys to constrain the mass function down to mass scales that typically host galaxies. Motivated by the proven accuracy of Press–Schechter-type mass functions, we introduce a related but purely empirical form consistent with standard formulae to better than 4% in the medium-mass regime, {10}^{10}\mbox{--}{10}^{13}\,{h}^{-1}M☉. In particular, our form consists of four parameters, each of which has a simple interpretation, and can be directly related to parameters of the galaxy distribution, such as {L}_{\star }$. Using this form within a hierarchical Bayesian likelihood model, we show how individual mass-measurement errors can be successfully included in a typical analysis, while accounting for Eddington bias. We apply our form to a question of survey design in the context of a semi-realistic data model, illustrating how it can be used to obtain optimal balance between survey depth and angular coverage for constraints on mass function parameters. Open-source Python and R codes to apply our new form are provided at http://mrpy.readthedocs.org and https://cran.r-project.org/web/packages/tggd/index.html respectively
Mind the Gap: Tightening the Mass-Richness Relation with Magnitude Gaps
We investigate the potential to improve optical tracers of cluster mass by
exploiting measurements of the magnitude gap, m12, defined as the difference
between the r-band absolute magnitude of the two brightest cluster members. We
find that in a mock sample of galaxy groups and clusters constructed from the
Bolshoi simulation, the scatter about the mass-richness relation decreases by
15-20% when magnitude gap information is included. A similar trend is evident
in a volume-limited, spectroscopic sample of galaxy groups observed in the
Sloan Digital Sky Survey (SDSS). We find that SDSS groups with small magnitude
gaps are richer than large-gap groups at fixed values of the one-dimensional
velocity dispersion among group members sigma_v, which we use as a mass proxy.
We demonstrate explicitly that m12 contains information about cluster mass that
supplements the information provided by group richness and the luminosity of
the brightest cluster galaxy, L_bcg. In so doing, we show that the luminosities
of the members of a group with richness N are inconsistent with the
distribution of luminosities that results from N random draws from the global
galaxy luminosity function. As the cosmological constraining power of galaxy
clusters is limited by the precision in cluster mass determination, our
findings suggest a new way to improve the cosmological constraints derived from
galaxy clusters.Comment: references adde
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