168 research outputs found
Disentangling the role of environmental processes in galaxy clusters
In this work we present the results of a novel approach devoted to
disentangle the role of the environmental processes affecting galaxies in
clusters. This is based on the analysis of the NUV-r' distributions of a large
sample of star-forming galaxies in clusters spanning more than four absolute
magnitudes. The galaxies inhabit three distinct environmental regions: virial
regions, cluster infall regions and field environment. We have applied rigorous
statistical tests in order to analyze both, the complete NUV-r' distributions
and their averages for three different bins of r'-band galaxy luminosity down
to M_r' ~ -18, throughout the three environmental regions considered. We have
identified the environmental processes that significantly affect the
star-forming galaxies in a given luminosity bin by using criteria based on the
characteristics of these processes: their typical time-scales, the regions
where they operate and the galaxy luminosity range for which their effects are
more intense. We have found that the high-luminosity (M_r'<=-20) star-forming
galaxies do not show significant signs in their star formation activity neither
of being affected by the environment in the last ~10^8 yr nor of a sudden
quenching in the last 1.5 Gyr. The intermediate-luminosity (-20<M_r'<=-19)
star-forming galaxies appear to be affected by starvation in the virial regions
and by the harassment both, in the virial and infall regions. Low-luminosity
(-19<M_r'<=-18.2) star-forming galaxies seem to be affected by the same
environmental processes as intermediate-luminosity star-forming galaxies in a
stronger way, as it would be expected for their lower luminosities.Comment: 42 pages, 7 figures, 5 tables; accepted for publication in Ap
AEGIS: The Nature of the Host Galaxies of Low-ionization Outflows at z < 0.6
We report on a S/N-limited search for low-ionization gas outflows in the
spectra of the 0.11 < z < 0.54 objects in the EGS portion of the DEEP2 survey.
Doppler shifts from the host galaxy redshifts are systematically searched for
in the Na I 5890,96 doublet (Na D). Although the spectral resolution and S/N
limit us to study the interstellar gas kinematics from fitting a single doublet
component to each observed Na D profile, the typical outflow often seen in
local luminous-infrared galaxies (LIRGs) should be detected at >~ 6 sigma in
absorption equivalent width down to the survey limiting S/N (~ 5 per pixel) in
the continuum around Na D. The detection rate of LIRG-like outflow clearly
shows an increasing trend with star-forming activity and infrared luminosity.
However, by virtue of not selecting our sample on star formation, we also find
a majority of outflows in galaxies on the red sequence in the rest-frame (U-B,
M_B) color-magnitude diagram. Most of these red-sequence outflows are of
early-type morphology and show the sign of recent star formation in their
UV-optical colors; some show enhanced Balmer H-beta absorption lines indicative
of poststarburst as well as high dust extinction. These findings demonstrate
that outflows outlive starbursts and suggest that galactic-scale outflows play
a role in quenching star formation in the host galaxies on their way to the red
sequence. The fate of relic winds, as well as the observational constraints on
gaseous feedback models, may be studied in galaxies during their poststarburst
phase. We also note the presence of inflow candidates in red, early-type
galaxies, some with signs of AGNs/LINERs but little evidence for star
formation.Comment: 19 pages & 19 figures (emulateapj); the revision to match the
published version in Ap
Halo Occupation Distribution Modeling of Green Valley Galaxies
We present a clustering analysis of near ultraviolet (NUV) - optical color
selected luminosity bin samples of green valley galaxies. These galaxy samples
are constructed by matching the Sloan Digital Sky Survey Data Release 7 with
the latest Galaxy Evolution Explorer source catalog which provides NUV
photometry. We present cross-correlation function measurements and determine
the halo occupation distribution of these transitional galaxies using a new
multiple tracer analysis technique.
We extend the halo-occupation formalism to model the cross-correlation
function between a galaxy sample of interest and multiple tracer populations
simultaneously. This method can be applied to commonly used luminosity
threshold samples as well as to color and luminosity bin selected galaxy
samples, and improves the accuracy of clustering analyses for sparse galaxy
populations.
We confirm the previously observed trend that red galaxies reside in more
massive halos and are more likely to be satellite galaxies than average
galaxies of similar luminosity. While the change in central galaxy host mass as
a function of color is only weakly constrained, the satellite fraction and
characteristic halo masses of green satellite galaxies are found to be
intermediate between those of blue and red satellite galaxies.Comment: matches MNRAS accepted version; minor revisions, results unchange
Are galaxies with AGN a transition population?
We present the results of an analysis of a well-selected sample of galaxies
with active and inactive galactic nuclei from the Sloan Digital Sky Survey, in
the range 0.01 < z < 0.16. The SDSS galaxy catalogue was split into two classes
of active galaxies, Type~2 AGN and composites, and one set of inactive,
star-forming/passive galaxies. For each active galaxy, two inactive control
galaxies were selected by matching redshift, absolute magnitude, inclination,
and radius. The sample of inactive galaxies naturally divides into a red and a
blue sequence, while the vast majority of AGN hosts occur along the red
sequence. In terms of H-alpha equivalent width, the population of composite
galaxies peaks in the valley between the two modes, suggesting a transition
population. However, this effect is not observed in other properties such as
colour-magnitude space, or colour-concentration plane. Active galaxies are seen
to be generally bulge-dominated systems, but with enhanced H-alpha emission
compared to inactive red-sequence galaxies. AGN and composites also occur in
less dense environments than inactive red-sequence galaxies, implying that the
fuelling of AGN is more restricted in high-density environments. These results
are therefore inconsistent with theories in which AGN host galaxies are a
`transition' population. We also introduce a systematic 3D spectroscopic
imaging survey, to quantify and compare the gaseous and stellar kinematics of a
well-selected, distance-limited sample of up to 20 nearby Seyfert galaxies, and
20 inactive control galaxies with well-matched optical properties. The survey
aims to search for dynamical triggers of nuclear activity and address
outstanding controversies in optical/IR imaging surveys.Comment: 12 pages, 8 figures, accepted by MNRA
Observational constraints on the co-evolution of supermassive black holes and galaxies
The star formation rate (SFR) and black hole accretion rate (BHAR) functions
are measured to be proportional to each other at z < ~3. This close
correspondence between SF and BHA would naturally yield a BH mass-galaxy mass
correlation, whereas a BH mass-bulge mass correlation is observed. To explore
this apparent contradiction we study the SF in spheroid-dominated galaxies
between z=1 and the present day. We use 903 galaxies from the COMBO-17 survey
with M* >2x10^10M_sun, ultraviolet and infrared-derived SFRs from Spitzer and
GALEX, and morphologies from GEMS HST/ACS imaging. Using stacking techniques,
we find that <25% of all SF occurs in spheroid-dominated galaxies (Sersic index
n>2.5), while the BHAR that we would expect if the global scalings held is
three times higher. This rules out the simplest picture of co-evolution, in
which SF and BHA trace each other at all times. These results could be
explained if SF and BHA occur in the same events, but offset in time, for
example at different stages of a merger event. However, one would then expect
to see the corresponding star formation activity in early-stage mergers, in
conflict with observations. We conclude that the major episodes of SF and BHA
occur in different events, with the bulk of SF happening in isolated disks and
most BHA occurring in major mergers. The apparent global co-evolution results
from the regulation of the BH growth by the potential well of the galactic
spheroid, which includes a major contribution from disrupted disk stars.Comment: 14 pages, 5 figures, accepted for publication in Ap
From Galaxy Clusters to Ultra-Faint Dwarf Spheroidals: A Fundamental Curve Connecting Dispersion-supported Galaxies to Their Dark Matter Halos
We examine scaling relations of dispersion-supported galaxies over more than
eight orders of magnitude in luminosity by transforming standard fundamental
plane parameters into a space of mass (M1/2), radius (r1/2), and luminosity
(L1/2). We find that from ultra-faint dwarf spheroidals to giant cluster
spheroids, dispersion-supported galaxies scatter about a one-dimensional
"fundamental curve" through this MRL space. The weakness of the M1/2-L1/2 slope
on the faint end may imply that potential well depth limits galaxy formation in
small galaxies, while the stronger dependence on L1/2 on the bright end
suggests that baryonic physics limits galaxy formation in massive galaxies. The
mass-radius projection of this curve can be compared to median dark matter halo
mass profiles of LCDM halos in order to construct a virial mass-luminosity
relationship (Mvir-L) for galaxies that spans seven orders of magnitude in
Mvir. Independent of any global abundance or clustering information, we find
that (spheroidal) galaxy formation needs to be most efficient in halos of Mvir
~ 10^12 Msun and to become inefficient above and below this scale. Moreover,
this profile matching technique is most accurate at the high and low luminosity
extremes (where dark matter fractions are highest) and is therefore quite
complementary to statistical approaches that rely on having a well-sampled
luminosity function. We also consider the significance and utility of the
scatter about this relation, and find that in the dSph regime observational
errors are almost at the point where we can explore the intrinsic scatter in
the luminosity-virial mass relation. Finally, we note that purely stellar
systems like Globular Clusters and Ultra Compact Dwarfs do not follow the
fundamental curve relation. This allows them to be easily distinguished from
dark-matter dominated dSph galaxies in MRL space. (abridged)Comment: 27 pages, 18 figures, ApJ accepted. High-res movies of 3D figures are
available at http://www.physics.uci.edu/~bullock/fcurve/movies.htm
Massive Galaxies in COSMOS: Evolution of Black hole versus bulge mass but not versus total stellar mass over the last 9 Gyrs?
We constrain the ratio of black hole (BH) mass to total stellar mass of
type-1 AGN in the COSMOS survey at 1<z<2. For 10 AGN at mean redshift z~1.4
with both HST/ACS and HST/NICMOS imaging data we are able to compute total
stellar mass M_(*,total), based on restframe UV-to-optical host galaxy colors
which constrain mass-to-light ratios. All objects have virial BH mass-estimates
available from the COSMOS Magellan/IMACS and zCOSMOS surveys. We find zero
difference between the M_BH--M_(*,total)-relation at z~1.4 and the
M_BH--M_(*,bulge)-relation in the local Universe.
Our interpretation is: (a) If our objects were purely bulge-dominated, the
M_BH--M_(*,bulge)-relation has not evolved since z~1.4. However, (b) since we
have evidence for substantial disk components, the bulges of massive galaxies
(logM_(*,total)=11.1+-0.25 or logM_BH~8.3+-0.2) must have grown over the last 9
Gyrs predominantly by redistribution of disk- into bulge-mass. Since all
necessary stellar mass exists in the galaxy at z=1.4, no star-formation or
addition of external stellar material is required, only a redistribution e.g.
induced by minor and major merging or through disk instabilities. Merging, in
addition to redistributing mass in the galaxy, will add both BH and
stellar/bulge mass, but does not change the overall final M_BH/M_(*,bulge)
ratio.
Since the overall cosmic stellar and BH mass buildup trace each other tightly
over time, our scenario of bulge-formation in massive galaxies is independent
of any strong BH-feedback and means that the mechanism coupling BH and bulge
mass until the present is very indirect.Comment: Published in ApJL; 7 pages, 2 figures; updated to accepted version
(methods changed, results unchanged
- …