97 research outputs found
Galaxy formation with cold gas accretion and evolving stellar initial mass function
The evolution of the galaxy stellar mass function is especially useful to
test the current model of galaxy formation. Observational data have revealed a
few inconsistencies with predictions from the model. For
example, most massive galaxies have already been observed at very high
redshifts, and they have experienced only mild evolution since then. In
conflict with this, semi-analytical models of galaxy formation predict an
insufficient number of massive galaxies at high redshift and a rapid evolution
between redshift 1 and 0 . In addition, there is a strong correlation between
star formation rate and stellar mass for star-forming galaxies, which can be
roughly reproduced with the model, but with a normalization that is too low at
high redshift. Furthermore, the stellar mass density obtained from the integral
of the cosmic star formation history is higher than the measured one by a
factor of 2. In this paper, we study these issues using a semi-analytical model
that includes: 1) cold gas accretion in massive halos at high redshift; 2)
tidal stripping of stellar mass from satellite galaxies; and 3) an evolving
stellar initial mass function (bottom-light) with a higher gas recycle
fraction. Our results show that the combined effects from 1) and 2) can predict
sufficiently massive galaxies at high redshifts and reproduce their mild
evolution at low redshift, While the combined effects of 1) and 3) can
reproduce the correlation between star formation rate and stellar mass for
star-forming galaxies across wide range of redshifts. A bottom-light/top-heavy
stellar IMF could partly resolve the conflict between the stellar mass density
and cosmic star formation history.Comment: 9 pages, 7 figures. Accepted for publication in Ap
Satellite Luminosities in Galaxy Groups
Halo model interpretations of the luminosity dependence of galaxy clustering
assume that there is a central galaxy in every sufficiently massive halo, and
that this central galaxy is very different from all the others in the halo. The
halo model decomposition makes the remarkable prediction that the mean
luminosity of the non-central galaxies in a halo should be almost independent
of halo mass: the predicted increase is about 20% while the halo mass increases
by a factor of more than 20. In contrast, the luminosity of the central object
is predicted to increase approximately linearly with halo mass at low to
intermediate masses, and logarithmically at high masses. We show that this
weak, almost non-existent mass-dependence of the satellites is in excellent
agreement with the satellite population in group catalogs constructed by two
different collaborations. This is remarkable, because the halo model prediction
was made without ever identifying groups and clusters. The halo model also
predicts that the number of satellites in a halo is drawn from a Poisson
distribution with mean which depends on halo mass. This, combined with the weak
dependence of satellite luminosity on halo mass, suggests that the Scott
effect, such that the luminosities of very bright galaxies are merely the
statistically extreme values of a general luminosity distribution, may better
apply to the most luminous satellite galaxy in a halo than to BCGs. If galaxies
are identified with halo substructure at the present time, then central
galaxies should be about 4 times more massive than satellite galaxies of the
same luminosity, whereas the differences between the stellar M/L ratios should
be smaller. Therefore, a comparison of the weak lensing signal from central and
satellite galaxies should provide useful constraints. [abridged]Comment: 8 pages, 3 figures. Matches version accepted by MNRA
Central and Satellite Colors in Galaxy Groups: A Comparison of the Halo Model and SDSS Group Catalogs
Current analytic and semi-analytic dark matter halo models distinguish
between the central galaxy in a halo and the satellite galaxies in halo
substructures. Using a recent halo-model description of the color dependence of
galaxy clustering (Skibba & Sheth 2008), we investigate the colors of central
and satellite galaxies predicted by the model and compare them to those of two
galaxy group catalogs constructed from the Sloan Digital Sky Survey (Yang et
al. 2007, Berlind et al. 2006a). In the model, the environmental dependence of
galaxy color is determined by that of halo mass, and the predicted color mark
correlations were shown to be consistent with SDSS measurements. The model
assumes that satellites tend to follow a color-magnitude sequence that
approaches the red sequence at bright luminosities; the model's success
suggests that bright satellites tend to be `red and dead' while the star
formation in fainter ones is in the process of being quenched. In both the
model and the SDSS group catalogs, we find that at fixed luminosity or stellar
mass, central galaxies tend to be bluer than satellites. In contrast, at fixed
group richness or halo mass, central galaxies tend to be redder than
satellites, and galaxy colors become redder with increasing mass. We also
compare the central and satellite galaxy color distributions, as a function of
luminosity and as a function of richness, in the model and in the two group
catalogs. Except for faint galaxies and small groups, the model and both group
catalogs are in very good agreement.Comment: 9 pages, 7 figures, revised version submitted to MNRAS. Significant
revisions were made, and figures were added showing the color distributions.
Important correction: the model and both group catalogs now have consistent
satellite colors--almost independent of group richnes
PRIMUS: The Effect of Physical Scale on the Luminosity-Dependence of Galaxy Clustering via Cross-Correlations
We report small-scale clustering measurements from the PRIMUS spectroscopic
redshift survey as a function of color and luminosity. We measure the
real-space cross-correlations between 62,106 primary galaxies with PRIMUS
redshifts and a tracer population of 545,000 photometric galaxies over
redshifts from z=0.2 to z=1. We separately fit a power-law model in redshift
and luminosity to each of three independent color-selected samples of galaxies.
We report clustering amplitudes at fiducial values of z=0.5 and L=1.5 L*. The
clustering of the red galaxies is ~3 times as strong as that of the blue
galaxies and ~1.5 as strong as that of the green galaxies. We also find that
the luminosity dependence of the clustering is strongly dependent on physical
scale, with greater luminosity dependence being found between r=0.0625 Mpc/h
and r=0.25 Mpc/h, compared to the r=0.5 Mpc/h to r=2 Mpc/h range. Moreover,
over a range of two orders of magnitude in luminosity, a single power-law fit
to the luminosity dependence is not sufficient to explain the increase in
clustering at both the bright and faint ends at the smaller scales. We argue
that luminosity-dependent clustering at small scales is a necessary component
of galaxy-halo occupation models for blue, star-forming galaxies as well as for
red, quenched galaxies.Comment: 13 pages, 6 figures, 5 tables; published in ApJ (revised to match
published version
Dark Matter Halo Models of Stellar Mass-Dependent Galaxy Clustering in PRIMUS+DEEP2 at 0.2<z<1.2
We utilize CDM halo occupation models of galaxy clustering to
investigate the evolving stellar mass dependent clustering of galaxies in the
PRIsm MUlti-object Survey (PRIMUS) and DEEP2 Redshift Survey over the past
eight billion years of cosmic time, between . These clustering
measurements provide new constraints on the connections between dark matter
halo properties and galaxy properties in the context of the evolving
large-scale structure of the universe. Using both an analytic model and a set
of mock galaxy catalogs, we find a strong correlation between central galaxy
stellar mass and dark matter halo mass over the range
-, approximately consistent
with previous observations and theoretical predictions. However, the
stellar-to-halo mass relation (SHMR) and the mass scale where star formation
efficiency reaches a maximum appear to evolve more strongly than predicted by
other models, including models based primarily on abundance-matching
constraints. We find that the fraction of satellite galaxies in haloes of a
given mass decreases significantly from to , partly due to
the fact that haloes at fixed mass are rarer at higher redshift and have lower
abundances. We also find that the ratio, a model parameter
that quantifies the critical mass above which haloes host at least one
satellite, decreases from at to at .
Considering the evolution of the subhalo mass function vis-\`{a}-vis satellite
abundances, this trend has implications for relations between satellite
galaxies and halo substructures and for intracluster mass, which we argue has
grown due to stripped and disrupted satellites between and
.Comment: 17 pages, 9 figures and 4 tables; Astrophysical Journal, publishe
PRIMUS + DEEP2: Clustering of X-ray, Radio and IR-AGN at z~0.7
We measure the clustering of X-ray, radio, and mid-IR-selected active
galactic nuclei (AGN) at 0.2 < z < 1.2 using multi-wavelength imaging and
spectroscopic redshifts from the PRIMUS and DEEP2 redshift surveys, covering 7
separate fields spanning ~10 square degrees. Using the cross-correlation of AGN
with dense galaxy samples, we measure the clustering scale length and slope, as
well as the bias, of AGN selected at different wavelengths. Similar to previous
studies, we find that X-ray and radio AGN are more clustered than
mid-IR-selected AGN. We further compare the clustering of each AGN sample with
matched galaxy samples designed to have the same stellar mass, star formation
rate, and redshift distributions as the AGN host galaxies and find no
significant differences between their clustering properties. The observed
differences in the clustering of AGN selected at different wavelengths can
therefore be explained by the clustering differences of their host populations,
which have different distributions in both stellar mass and star formation
rate. Selection biases inherent in AGN selection, therefore, determine the
clustering of observed AGN samples. We further find no significant difference
between the clustering of obscured and unobscured AGN, using IRAC or WISE
colors or X-ray hardness ratio.Comment: Accepted to ApJ. 23 emulateapj pages, 15 figures, 4 table
Galaxy Zoo: Disentangling the Environmental Dependence of Morphology and Colour
We analyze the environmental dependence of galaxy morphology and colour with
two-point clustering statistics, using data from the Galaxy Zoo, the largest
sample of visually classified morphologies yet compiled, extracted from the
Sloan Digital Sky Survey. We present two-point correlation functions of spiral
and early-type galaxies, and we quantify the correlation between morphology and
environment with marked correlation functions. These yield clear and precise
environmental trends across a wide range of scales, analogous to similar
measurements with galaxy colours, indicating that the Galaxy Zoo
classifications themselves are very precise. We measure morphology marked
correlation functions at fixed colour and find that they are relatively weak,
with the only residual correlation being that of red galaxies at small scales,
indicating a morphology gradient within haloes for red galaxies. At fixed
morphology, we find that the environmental dependence of colour remains strong,
and these correlations remain for fixed morphology \textit{and} luminosity. An
implication of this is that much of the morphology--density relation is due to
the relation between colour and density. Our results also have implications for
galaxy evolution: the morphological transformation of galaxies is usually
accompanied by a colour transformation, but not necessarily vice versa. A
spiral galaxy may move onto the red sequence of the colour-magnitude diagram
without quickly becoming an early-type. We analyze the significant population
of red spiral galaxies, and present evidence that they tend to be located in
moderately dense environments and are often satellite galaxies in the outskirts
of haloes. Finally, we combine our results to argue that central and satellite
galaxies tend to follow different evolutionary paths.Comment: 19 pages, 18 figures. Accepted for publication in MNRA
PRIMUS: Galaxy Clustering as a Function of Luminosity and Color at 0.2<z<1
We present measurements of the luminosity and color-dependence of galaxy
clustering at 0.2<z<1.0 in the PRIsm MUlti-object Survey (PRIMUS). We quantify
the clustering with the redshift-space and projected two-point correlation
functions, xi(rp,pi) and wp(rp), using volume-limited samples constructed from
a parent sample of over 130,000 galaxies with robust redshifts in seven
independent fields covering 9 sq. deg. of sky. We quantify how the
scale-dependent clustering amplitude increases with increasing luminosity and
redder color, with relatively small errors over large volumes. We find that red
galaxies have stronger small-scale (0.1<rp<1 Mpc/h) clustering and steeper
correlation functions compared to blue galaxies, as well as a strong color
dependent clustering within the red sequence alone. We interpret our measured
clustering trends in terms of galaxy bias and obtain values between
b_gal=0.9-2.5, quantifying how galaxies are biased tracers of dark matter
depending on their luminosity and color. We also interpret the color dependence
with mock catalogs, and find that the clustering of blue galaxies is nearly
constant with color, while redder galaxies have stronger clustering in the
one-halo term due to a higher satellite galaxy fraction. In addition, we
measure the evolution of the clustering strength and bias, and we do not detect
statistically significant departures from passive evolution. We argue that the
luminosity- and color-environment (or halo mass) relations of galaxies have not
significantly evolved since z=1. Finally, using jackknife subsampling methods,
we find that sampling fluctuations are important and that the COSMOS field is
generally an outlier, due to having more overdense structures than other
fields; we find that 'cosmic variance' can be a significant source of
uncertainty for high-redshift clustering measurements.Comment: 22 pages, 21 figures, matches version published in Ap
- …