258 research outputs found
The stellar-subhalo mass relation of satellite galaxies
We extend the abundance matching technique (AMT) to infer the
satellite-subhalo and central-halo mass relations (MRs) of galaxies, as well as
the corresponding satellite conditional mass functions (CMFs). We use the
observed galaxy stellar mass function (GSMF) decomposed into centrals and
satellites and the LCDM halo/subhalo mass functions as inputs. We explore the
effects of defining the subhalo mass at the time of accretion (m_acc) vs. at
the time of observation (m_obs). We test the standard assumption that centrals
and satellites follow the same MRs, showing that this assumption leads to
predictions in disagreement with observations, specially for m_obs. Instead,
when the satellite-subhalo MRs are constrained following our AMT, they are
always different from the central-halo MR: the smaller the stellar mass (Ms),
the less massive is the subhalo of satellites as compared to the halo of
centrals of the same Ms. On average, for Ms<2x10^11Msol, the dark mass of
satellites decreased by 60-65% with respect to their masses at accretion time.
The resulting MRs for both definitions of subhalo mass yield satellite CMFs in
agreement with observations. Also, when these MRs are used in a HOD model, the
predicted correlation functions agree with observations. We show that the use
of m_obs leads to less uncertain MRs than m_acc, and discuss implications of
the obtained satellite-subhalo MR. For example, we show that the tension
between abundance and dynamics of MW satellites in LCDM gives if the slope of
the GSMF faint-end slope upturns to -1.6.Comment: 13, pages, 4 figures. Accepted for publication in ApJ. Minor changes
to previous versio
Galaxy downsizing evidenced by hybrid evolutionary tracks
An unified picture of stellar and halo mass build-up as a function of mass is
presented. Inferred stellar-dark halo mass relations of galaxies, Ms-Mh, out to
z=4 together with average LCDM halo mass aggregation histories (MAHs) are used
for inferring average Ms growth histories, the Galaxian Hybrid Evolutionary
Tracks (GHETs). The more massive the galaxy, the earlier transited in average
from an active regime of Ms growth to a passive one:
log(Mtran/Msun)=10.30+0.55z ("population downsizing"), where Mtran is the
typical transition stellar mass. This result agrees with independent
observational determinations based on the evolution of the galaxy stellar mass
function decomposition into blue and red galaxies. The specific star formation
rate, SSFR, predicted from the derivative of the GHET is consistent with direct
measures of the SSFR for galaxies at different z's. The average GHETs of
galaxies smaller than Mtran at z=0 (Ms~10^10.3 Msun) did not reach the
quiescent regime, and for them, the lower the mass, the faster the later Ms
growth rate ("downsizing in SSFR"). The GHETs allow to predict the transition
rate in number density of active to passive population; the predicted values
agree with direct estimates of growth rate in number density for the (massive)
red population up to z~1. We show that LCDM-based models of disk galaxy
evolution are able to reproduce the low-mass side of the Ms-Mh relation at z~0,
but at higher z's disagree strongly with the GHETs: models do not reproduce the
downsizing in SSFR and the high SSFR of low mass galaxies. (Abridged)Comment: 14 pages, 9 figures. To appear in ApJ. References updated/corrected,
minor typos correcte
Extremely compact massive galaxies at z~1.4
The optical rest-frame sizes of 10 of the most massive
(~5x10^{11}h_{70}^{-2}M_sun) galaxies found in the near-infrared MUNICS survey
at 1.2<z<1.7 are analysed. Sizes were estimated both in the J and K' filters.
These massive galaxies are at least a factor of 4_{-1.0}^{+1.9} (+-1 sigma)
smaller in the rest-frame V-band than local counterparts of the same stellar
mass. Consequently, the stellar mass density of these objects is (at least) 60
times larger than massive ellipticals today. Although the stellar populations
of these objects are passively fading, their structural properties are rapidly
changing since that redshift. This observational fact disagrees with a scenario
where the more massive and passive galaxies are fully assembled at z~1.4 (i.e.
a monolithic scenario) and points towards a dry merger scenario as the
responsible mechanism for the subsequent evolution of these galaxies.Comment: 5 pages, 2 figures, 1 table, accepted for publication in MNRAS
letter
The Molecular Gas Content of z<0.1 Radio Galaxies: Linking the AGN Accretion Mode to Host Galaxy Properties
One of the main achievements in modern cosmology is the so-called `unified
model', which successfully describes most classes of active galactic nuclei
(AGN) within a single physical scheme. However, there is a particular class of
radio-luminous AGN that presently cannot be explained within this framework --
the `low-excitation' radio AGN (LERAGN). Recently, a scenario has been put
forward which predicts that LERAGN, and their regular `high-excitation' radio
AGN (HERAGN) counterparts represent different (red sequence vs. green valley)
phases of galaxy evolution. These different evolutionary states are also
expected to be reflected in their host galaxy properties, in particular their
cold gas content. To test this, here we present CO(1-0) observations toward a
sample of 11 of these systems conducted with CARMA. Combining our observations
with literature data, we derive molecular gas masses (or upper limits) for a
complete, representative, sample of 21 z<0.1 radio AGN. Our results yield that
HERAGN on average have a factor of ~7 higher gas masses than LERAGN. We also
infer younger stellar ages, lower stellar, halo, and central supermassive black
masses, as well as higher black hole accretion efficiencies in HERAGN relative
to LERAGN. These findings support the idea that high- and low-excitation radio
AGN form two physically distinct populations of galaxies that reflect different
stages of massive galaxy build-up.Comment: 8 pages, 4 figures, 4 tables; accepted for publication in Ap
Constraints on the relationship between stellar mass and halo mass at low and high redshift
We use a statistical approach to determine the relationship between the
stellar masses of galaxies and the masses of the dark matter halos in which
they reside. We obtain a parameterized stellar-to-halo mass (SHM) relation by
populating halos and subhalos in an N-body simulation with galaxies and
requiring that the observed stellar mass function be reproduced. We find good
agreement with constraints from galaxy-galaxy lensing and predictions of
semi-analytic models. Using this mapping, and the positions of the halos and
subhalos obtained from the simulation, we find that our model predictions for
the galaxy two-point correlation function (CF) as a function of stellar mass
are in excellent agreement with the observed clustering properties in the SDSS
at z=0. We show that the clustering data do not provide additional strong
constraints on the SHM function and conclude that our model can therefore
predict clustering as a function of stellar mass. We compute the conditional
mass function, which yields the average number of galaxies with stellar masses
in the range [m, m+dm] that reside in a halo of mass M. We study the redshift
dependence of the SHM relation and show that, for low mass halos, the SHM ratio
is lower at higher redshift. The derived SHM relation is used to predict the
stellar mass dependent galaxy CF and bias at high redshift. Our model predicts
that not only are massive galaxies more biased than low mass ones at all
redshifts, but the bias increases more rapidly with increasing redshift for
massive galaxies than for low mass ones. We present convenient fitting
functions for the SHM relation as a function of redshift, the conditional mass
function, and the bias as a function of stellar mass and redshift.Comment: 21 pages, 17 figures, discussion enlarged, one more figure, updated
references, accepted for publication in Ap
HI Rich but Low Star Formation galaxies in MaNGA: Physical Properties and Comparison to Control Samples
Gas rich galaxies are typically star-forming. We make use of HI-MaNGA, a
program of HI follow-up for the Mapping Nearby Galaxies at Apache Point
Observatory (MaNGA) survey of the Sloan Digital Sky Surveys to construct a
sample of unusual neutral hydrogen (HI, 21cm) rich galaxies which have low Star
Formation Rates (SFRs); using infra-red color from the Wide-field Infrared
Survey Explorer (WISE) as a proxy for specific SFR. Out of a set of 1575 MaNGA
galaxies with HI-MaNGA detections, we find 83 (5%) meet our selection criteria
to be HI rich with low SFR. We construct two stellar mass-matched control
samples: HI rich galaxies with typical SFR (High SF Control) and HI poor
galaxies with low SFR (Low HI Control). We investigate the properties of each
of these samples, comparing physical parameters such as ionization state maps,
stellar and ionized gas velocity and dispersion, environment measures,
metallicity, and morphology to search for the reasons why these unusual HI rich
galaxies are not forming stars. We find evidence for recent external accretion
of gas in some galaxies (via high counter-rotating fractions), along with some
evidence for AGN feedback (from a high cLIER and/or red geyser fraction), and
bar quenching (via an enhanced strong bar fraction). Some galaxies in the
sample are consistent with simply having their HI in a high angular momentum,
large radius, low density disc. We conclude that no single physical process can
explain all HI rich, low SFR galaxies.Comment: 15 pages, in press MNRAS. v2 following corrections noticed in proof
The density of very massive evolved galaxies to z~1.7
We spectroscopically identified 7 massive evolved galaxies with magnitudes
17.8<K<18.4 at 1.3<z<1.7 over an area of ~160 arcmin^2 of the MUNICS survey.
Their rest-frame K-band absolute magnitudes are -26.8<M$_K<-26.1 (5L*<L_K<10L*)
and the resulting stellar masses are in the range 3-6.5x10^{11} M_sun. The
analysis we performed unambiguously shows the early-type nature of their
spectra. The 7 massive evolved galaxies account for a comoving density of
\~5.5(+-2) x 10^{-5} Mpc^{-3} at ~1.5, a factor 1.5 lower than the density
(8.4(+-1) x 10^{-5} Mpc^{-3}) of early-types with comparable masses at z=0. The
incompleteness (30%) of our spectroscopic observations accounts for this
discrepancy. Thus, our data do not support a decrease of the comoving density
of early-type galaxies with masses comparable to the most massive ones in the
local Universe up to z~1.7. This suggests that massive evolved galaxies do not
play an important role in the evolution of the mass density outlined by recent
surveys in this redshift range, evolution which instead has to be ascribed to
the accretion of the stellar mass in late-type galaxies. Finally, the presence
of such massive evolved galaxies at these redshifts suggests that the assembly
of massive spheroids has taken place at z>2 supporting a high efficiency in the
accretion of the stellar mass in massive halos in the early Universe.Comment: Accepted for publication in MNRAS Letters, 5 pages, 3 figure
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