106 research outputs found
The DEEP2 Galaxy Redshift Survey: Mean Ages and Metallicities of Red Field Galaxies at z ~ 0.9 from Stacked Keck/DEIMOS Spectra
As part of the DEEP2 galaxy redshift survey, we analyze absorption line
strengths in stacked Keck/DEIMOS spectra of red field galaxies with weak to no
emission lines, at redshifts 0.7 <= z <= 1. Comparison with models of stellar
population synthesis shows that red galaxies at z ~ 0.9 have mean
luminosity-weighted ages of the order of only 1 Gyr and at least solar
metallicities. This result cannot be reconciled with a scenario where all stars
evolved passively after forming at very high z. Rather, a significant fraction
of stars can be no more than 1 Gyr old, which means that star formation
continued to at least z ~ 1.2. Furthermore, a comparison of these distant
galaxies with a local SDSS sample, using stellar populations synthesis models,
shows that the drop in the equivalent width of Hdelta from z ~ 0.9 to 0.1 is
less than predicted by passively evolving models. This admits of two
interpretations: either each individual galaxy experiences continuing low-level
star formation, or the red-sequence galaxy population from z ~ 0.9 to 0.1 is
continually being added to by new galaxies with younger stars.Comment: A few typos were corrected and numbers in Table 1 were revise
Dependence of Galaxy Quenching on Halo Mass and Distance from its Centre
We study the dependence of star-formation quenching on galaxy mass and
environment, in the SDSS (z~0.1) and the AEGIS (z~1). It is crucial that we
define quenching by low star-formation rate rather than by red colour, given
that one third of the red galaxies are star forming. We address stellar mass
M*, halo mass Mh, density over the nearest N neighbours deltaN, and distance to
the halo centre D. The fraction of quenched galaxies appears more strongly
correlated with Mh at fixed M* than with M* at fixed Mh, while for satellites
quenching also depends on D. We present the M*-Mh relation for centrals at z~1.
At z~1, the dependence of quenching on M* at fixed Mh is somewhat more
pronounced than at z~0, but the quenched fraction is low (10%) and the haloes
are less massive. For satellites, M*-dependent quenching is noticeable at high
D, suggesting a quenching dependence on sub-halo mass for recently captured
satellites. At small D, where satellites likely fell in more than a few Gyr
ago, quenching strongly depends on Mh, and not on M*. The Mh-dependence of
quenching is consistent with theoretical wisdom where virial shock heating in
massive haloes shuts down accretion and triggers ram-pressure stripping,
causing quenching. The interpretation of deltaN is complicated by the fact that
it depends on the number of observed group members compared to N, motivating
the use of D as a better measure of local environment.Comment: 23 pages, 13 figures, accepted by MNRA
The DEEP3 Galaxy Redshift Survey: The Impact of Environment on the Size Evolution of Massive Early-type Galaxies at Intermediate Redshift
Using data drawn from the DEEP2 and DEEP3 Galaxy Redshift Surveys, we
investigate the relationship between the environment and the structure of
galaxies residing on the red sequence at intermediate redshift. Within the
massive (10 < log(M*/Msun) < 11) early-type population at 0.4 < z <1.2, we find
a significant correlation between local galaxy overdensity (or environment) and
galaxy size, such that early-type systems in higher-density regions tend to
have larger effective radii (by ~0.5 kpc or 25% larger) than their counterparts
of equal stellar mass and Sersic index in lower-density environments. This
observed size-density relation is consistent with a model of galaxy formation
in which the evolution of early-type systems at z < 2 is accelerated in
high-density environments such as groups and clusters and in which dry, minor
mergers (versus mechanisms such as quasar feedback) play a central role in the
structural evolution of the massive, early-type galaxy population.Comment: 11 pages, 5 figures, 2 tables; resubmitted to MNRAS after addressing
referee's comments (originally submitted to journal on August 16, 2011
Development of bovine abomasal organoids as a novel in-vitro model to study host-parasite interactions in gastrointestinal nematode infections
Gastro-intestinal nematode (GIN) parasites are a major cause of production losses in grazing cattle, primarily through reduced growth rates in young animals. Control of these parasites relies heavily on anthelmintic drugs; however, with growing reports of resistance to currently available anthelmintics, alternative methods of control are required. A major hurdle in this work has been the lack of physiologically relevant in vitro infection models that has made studying precise interactions between the host and the GINs difficult. Such mechanistic insights into the infection process will be valuable for the development of novel targets for drugs, vaccines, or other interventions. Here we created bovine gastric epithelial organoids from abomasal gastric tissue and studied their application as in vitro models for understanding host invasion by GIN parasites. Transcriptomic analysis of gastric organoids across multiple passages and the corresponding abomasal tissue showed conserved expression of tissue-specific genes across samples, demonstrating that the organoids are representative of bovine gastric tissue from which they were derived. We also show that self-renewing and self-organising three-dimensional organoids can also be serially passaged, cryopreserved, and resuscitated. Using Ostertagia ostertagi, the most pathogenic gastric parasite in cattle in temperate regions, we show that cattle gastric organoids are biologically relevant models for studying GIN invasion in the bovine abomasum. Within 24Â h of exposure, exsheathed larvae rapidly and repeatedly infiltrated the lumen of the organoids. Prior to invasion by the parasites, the abomasal organoids rapidly expanded, developing a âballooningâ phenotype. Ballooning of the organoids could also be induced in response to exposure to parasite excretory/secretory products. In summary, we demonstrate the power of using abomasal organoids as a physiologically relevant in vitro model system to study interactions of O. ostertagi and other GIN with bovine gastrointestinal epithelium
Science Objectives and Early Results of the DEEP2 Redshift Survey
The DEIMOS spectrograph has now been installed on the Keck-II telescope and
commissioning is nearly complete. The DEEP2 Redshift Survey, which will take
approximately 120 nights at the Keck Observatory over a three year period and
has been designed to utilize the power of DEIMOS, began in the summer of 2002.
The multiplexing power and high efficiency of DEIMOS enables us to target 1000
faint galaxies per clear night. Our goal is to gather high-quality spectra of
\~60,000 galaxies with z>0.75 in order to study the properties and large scale
clustering of galaxies at z ~ 1. The survey will be executed at high spectral
resolution, , allowing us to work
between the bright OH sky emission lines and to infer linewidths for many of
the target galaxies (for several thousand objects, we will obtain rotation
curves as well). The linewidth data will facilitate the execution of the
classical redshift-volume cosmological test, which can provide a precision
measurement of the equation of state of the Universe. This talk reviews the
project, summarizes our science goals and presents some early DEIMOS data.Comment: 12 pages, 5 figures, talk presented at SPIE conference, Aug. 200
Stellar Mass--Gas-phase Metallicity Relation at : A Power Law with Increasing Scatter toward the Low-mass Regime
We present the stellar mass ()--gas-phase metallicity relation (MZR)
and its scatter at intermediate redshifts () for 1381 field
galaxies collected from deep spectroscopic surveys. The star formation rate
(SFR) and color at a given of this magnitude-limited ( AB)
sample are representative of normal star-forming galaxies. For masses below
, our sample of 237 galaxies is 10 times larger than those
in previous studies beyond the local universe. This huge gain in sample size
enables superior constraints on the MZR and its scatter in the low-mass regime.
We find a power-law MZR at :
. Our MZR
shows good agreement with others measured at similar redshifts in the
literature in the intermediate and massive regimes, but is shallower than the
extrapolation of the MZRs of others to masses below . The SFR
dependence of the MZR in our sample is weaker than that found for local
galaxies (known as the Fundamental Metallicity Relation). Compared to a variety
of theoretical models, the slope of our MZR for low-mass galaxies agrees well
with predictions incorporating supernova energy-driven winds. Being robust
against currently uncertain metallicity calibrations, the scatter of the MZR
serves as a powerful diagnostic of the stochastic history of gas accretion, gas
recycling, and star formation of low-mass galaxies. Our major result is that
the scatter of our MZR increases as decreases. Our result implies that
either the scatter of the baryonic accretion rate or the scatter of the
-- relation increases as decreases. Moreover, our
measures of scatter at appears consistent with that found for local
galaxies.Comment: 18 pages, 10 figures. Accepted by ApJ. Typos correcte
The DEEP2 Galaxy Redshift Survey: Color and Luminosity Dependence of Galaxy Clustering at z~1
We present measurements of the color and luminosity dependence of galaxy
clustering at z~1 in the DEEP2 Galaxy Redshift Survey. Using volume-limited
subsamples in bins of both color and luminosity, we find that: 1) The
clustering dependence is much stronger with color than with luminosity and is
as strong with color at z~1 as is found locally. We find no dependence of the
clustering amplitude on color for galaxies on the red sequence, but a
significant dependence on color for galaxies within the blue cloud. 2) For
galaxies in the range L/L*~0.7-2, a stronger large-scale luminosity dependence
is seen for all galaxies than for red and blue galaxies separately. The
small-scale clustering amplitude depends significantly on luminosity for blue
galaxies, with brighter samples having a stronger rise on scales r_p<0.5 Mpc/h.
3) Redder galaxies exhibit stronger small-scale redshift-space distortions
("fingers of god"), and both red and blue populations show large-scale
distortions in xi(r_p,pi) due to coherent infall. 4) While the clustering
length, r_0, increases smoothly with galaxy color (in narrow bins), its
power-law exponent, gamma, exhibits a sharp jump from the blue cloud to the red
sequence. The intermediate color `green' galaxy population likely includes
transitional galaxies moving from the blue cloud to the red sequence; on large
scales green galaxies are as clustered as red galaxies but show infall
kinematics and a small-scale correlation slope akin to the blue galaxy
population. 5) We compare our results to a semi-analytic galaxy formation model
applied to the Millenium Run simulation. Differences between the data and the
model suggest that in the model star formation is shut down too efficiently in
satellite galaxies.Comment: 28 pages, 17 figures, emulateapj format, accepted to ApJ, updated to
match published versio
The DEEP2 Galaxy Redshift Survey: The Voronoi-Delaunay Method Catalog of Galaxy Groups
We present a public catalog of galaxy groups constructed from the spectroscopic sample of galaxies in the fourth data release from the Deep Extragalactic Evolutionary Probe 2 (DEEP2) Galaxy Redshift Survey, including the Extended Groth Strip (EGS). The catalog contains 1165 groups with two or more members in the EGS over the redshift range 0 0.6 in the rest of DEEP2. Twenty-five percent of EGS galaxies and fourteen percent of high-z DEEP2 galaxies are assigned to galaxy groups. The groups were detected using the Voronoi-Delaunay method (VDM) after it has been optimized on mock DEEP2 catalogs following similar methods to those employed in Gerke et al. In the optimization effort, we have taken particular care to ensure that the mock catalogs resemble the data as closely as possible, and we have fine-tuned our methods separately on mocks constructed for the EGS and the rest of DEEP2. We have also probed the effect of the assumed cosmology on our inferred group-finding efficiency by performing our optimization on three different mock catalogs with different background cosmologies, finding large differences in the group-finding success we can achieve for these different mocks. Using the mock catalog whose background cosmology is most consistent with current data, we estimate that the DEEP2 group catalog is 72% complete and 61% pure (74% and 67% for the EGS) and that the group finder correctly classifies 70% of galaxies that truly belong to groups, with an additional 46% of interloper galaxies contaminating the catalog (66% and 43% for the EGS). We also confirm that the VDM catalog reconstructs the abundance of galaxy groups with velocity dispersions above ~300 km s^(â1) to an accuracy better than the sample variance, and this successful reconstruction is not strongly dependent on cosmology. This makes the DEEP2 group catalog a promising probe of the growth of cosmic structure that can potentially be used for cosmological tests
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