501 research outputs found
The dynamics of z~1 clusters of galaxies from the GCLASS survey
We constrain the internal dynamics of a stack of 10 clusters from the GCLASS
survey at 0.87<z<1.34. We determine the stack cluster mass profile M(r) using
the MAMPOSSt algorithm of Mamon et al., the velocity anisotropy profile beta(r)
from the inversion of the Jeans equation, and the pseudo-phase-space density
profiles Q(r) and Qr(r), obtained from the ratio between the mass density
profile and the third power of the (total and, respectively, radial) velocity
dispersion profiles of cluster galaxies. Several M(r) models are statistically
acceptable for the stack cluster (Burkert, Einasto, Hernquist, NFW). The total
mass distribution has a concentration c=r200/r-2=4.0-0.6+1.0, in agreement with
theoretical expectations, and is less concentrated than the cluster
stellar-mass distribution. The stack cluster beta(r) is similar for passive and
star-forming galaxies and indicates isotropic galaxy orbits near the cluster
center and increasingly radially elongated with increasing cluster-centric
distance. Q(r) and Qr(r) are almost power-law relations with slopes similar to
those predicted from numerical simulations of dark matter halos. Combined with
results obtained for lower-z clusters we determine the dynamical evolution of
galaxy clusters, and compare it with theoretical predictions. We discuss
possible physical mechanisms responsible for the differential evolution of
total and stellar mass concentrations, and of passive and star-forming galaxy
orbits [abridged].Comment: 12 pages, 7 figures. Version accepted for publication in A&A after
minor modification
A Kinematic Approach To Assessing Environmental Effects: Star-Forming Galaxies in a z~0.9 SpARCS cluster using Spitzer 24um Observations
We present an infrared study of a z=0.872 cluster, SpARCS J161314+564930,
with the primary aim of distinguishing the dynamical histories of
spectroscopically confirmed star-forming members to assess the role of cluster
environment. We utilize deep MIPS imaging and a mass-limited sample of 85
spectroscopic members to identify 16 24um-bright sources within the cluster,
and measure their 24um star formation rates (SFRs) down to ~6 Msolar/year.
Based on their line-of-sight velocities and stellar ages, MIPS cluster members
appear to be an infalling population that was recently accreted from the field
with minimal environmental dependency on their star formation. However, we
identify a double-sequenced distribution of star-forming galaxies amongst the
members, with one branch exhibiting declining specific SFRs with mass. The
members along this sub-main sequence contain spectral features suggestive of
passive galaxies. Using caustic diagrams, we kinematically identify these
galaxies as a virialized and/or backsplash population. Moreover, we find a mix
of dynamical histories at all projected radii, indicating that standard
definitions of environment (i.e., radius and density) are contaminated with
recently accreted interlopers, which could contribute to a lack of
environmental trends for star-forming galaxies. A cleaner narrative of their
dynamical past begins to unfold when using a proxy for accretion histories
through profiles of constant (r/r_200)x(Delta v/sigma_v); galaxies accreted at
earlier times possess lower values of (r/r_200)x(Delta v/sigma_v) with minimal
contamination from the distinct infalling population. Therefore, adopting a
time-averaged definition for density (as traced by accretion histories) rather
than an instantaneous density yields a depressed specific SFR within the
dynamical cluster core.Comment: 14 pages, 10 figures, 1 table; accepted for publication in Ap
The Phase Space and Stellar Populations of Cluster Galaxies at z ~ 1: Simultaneous Constraints on the Location and Timescale of Satellite Quenching
We investigate the velocity vs. position phase space of z ~ 1 cluster
galaxies using a set of 424 spectroscopic redshifts in 9 clusters drawn from
the GCLASS survey. Dividing the galaxy population into three categories:
quiescent, star-forming, and poststarburst, we find that these populations have
distinct distributions in phase space. Most striking are the poststarburst
galaxies, which are commonly found at small clustercentric radii with high
clustercentric velocities, and appear to trace a coherent ``ring" in phase
space. Using several zoom simulations of clusters we show that the coherent
distribution of the poststarbursts can be reasonably well-reproduced using a
simple quenching scenario. Specifically, the phase space is best reproduced if
satellite quenching occurs on a rapid timescale (0.1 < tau_{Q} < 0.5 Gyr) after
galaxies make their first passage of R ~ 0.5R_{200}, a process that takes a
total time of ~ 1 Gyr after first infall. We compare this quenching timescale
to the timescale implied by the stellar populations of the poststarburst
galaxies and find that the poststarburst spectra are well-fit by a rapid
quenching (tau_{Q} = 0.4^{+0.3}_{-0.4} Gyr) of a typical star-forming galaxy.
The similarity between the quenching timescales derived from these independent
indicators is a strong consistency check of the quenching model. Given that the
model implies satellite quenching is rapid, and occurs well within R_{200},
this would suggest that ram-pressure stripping of either the hot or cold gas
component of galaxies are the most plausible candidates for the physical
mechanism. The high cold gas consumption rates at z ~ 1 make it difficult to
determine if hot or cold gas stripping is dominant; however, measurements of
the redshift evolution of the satellite quenching timescale and location may be
capable of distinguishing between the two.Comment: 10 pages, 4 figures, submitted to the Ap
Identification of major dioxin-like compounds and androgen receptor antagonist in acid-treated tissue extracts of high trophic-level animals
We evaluated the applicability of combining in vitro bioassays with instrument analyses to identify potential endocrine disrupting pollutants in sulfuric acid-treated extracts of liver and/or blubber of high trophic-level animals. Dioxin-like and androgen receptor (AR) antagonistic activities were observed in Baikal seals, common cormorants, raccoon dogs, and finless porpoises by using a panel of rat and human cell-based chemical-activated luciferase gene expression (CALUX) reporter gene bioassays. On the other hand, no activity was detected in estrogen receptor α (ERα)-, glucocorticoid receptor (GR)-, progesterone receptor (PR)-, and peroxisome proliferator-activated receptor γ2 (PPARγ2)-CALUX assays with the sample amount applied. All individual samples (n = 66) showed dioxin-like activity, with values ranging from 21 to 5500 pg CALUX-2,3,7,8-tetrachlorodibenzo-p-dioxin equivalent (TEQ)/g-lipid. Because dioxins are expected to be strong contributors to CALUX-TEQs, the median theoretical contribution of dioxins calculated from the result of chemical analysis to the experimental CALUX-TEQs was estimated to explain up to 130% for all the tested samples (n = 54). Baikal seal extracts (n = 31), but not other extracts, induced AR antagonistic activities that were 8-150 μg CALUX-flutamide equivalent (FluEQ)/g-lipid. p,p′-DDE was identified as an important causative compound for the activity, and its median theoretical contribution to the experimental CALUX-FluEQs was 59% for the tested Baikal seal tissues (n = 25). Our results demonstrate that combining in vitro CALUX assays with instrument analysis is useful for identifying persistent organic pollutant-like compounds in the tissue of wild animals on the basis of in vitro endocrine disruption toxicity. © 2011 American Chemical Society
The Evolution of Environmental Quenching Timescales to
Using a sample of 4 galaxy clusters at and 10 galaxy
clusters at , we measure the environmental quenching
timescale, , corresponding to the time required after a galaxy is accreted
by a cluster for it to fully cease star formation. Cluster members are selected
by a photometric-redshift criterion, and categorized as star-forming,
quiescent, or intermediate according to their dust-corrected rest-frame colors
and magnitudes. We employ a "delayed-then-rapid" quenching model that relates a
simulated cluster mass accretion rate to the observed numbers of each type of
galaxy in the cluster to constrain . For galaxies of mass , we find a quenching timescale of 1.24 Gyr
in the cluster sample, and 1.50 Gyr at . Using values
drawn from the literature, we compare the redshift evolution of to
timescales predicted for different physical quenching mechanisms. We find
to depend on host halo mass such that quenching occurs over faster timescales
in clusters relative to groups, suggesting that properties of the host halo are
responsible for quenching high-mass galaxies. Between and , we
find that evolves faster than the molecular gas depletion timescale and
slower than an SFR-outflow timescale, but is consistent with the evolution of
the dynamical time. This suggests that environmental quenching in these
galaxies is driven by the motion of satellites relative to the cluster
environment, although due to uncertainties in the atomic gas budget at high
redshift, we cannot rule out quenching due to simple gas depletion
Performance of serum-supplemented and serum-free media in IFNγ Elispot Assays for human T cells
The choice of serum for supplementation of media for T cell assays and in particular, Elispot has been a major challenge for assay performance, standardization, optimization, and reproducibility. The Assay Working Group of the Cancer Vaccine Consortium (CVC-CRI) has recently identified the choice of serum to be the leading cause for variability and suboptimal performance in large international Elispot proficiency panels. Therefore, a serum task force was initiated to compare the performance of commercially available serum-free media to laboratories’ own medium/serum combinations. The objective of this project was to investigate whether a serum-free medium exists that performs as well as lab-own serum/media combinations with regard to antigen-specific responses and background reactivity in Elispot. In this way, a straightforward solution could be provided to address the serum challenge. Eleven laboratories tested peripheral blood mononuclear cells (PBMC) from four donors for their reactivity against two peptide pools, following their own Standard Operating Procedure (SOP). Each laboratory performed five simultaneous experiments with the same SOP, the only difference between the experiments was the medium used. The five media were lab-own serum-supplemented medium, AIM-V, CTL, Optmizer, and X-Vivo. The serum task force results demonstrate compellingly that serum-free media perform as well as qualified medium/serum combinations, independent of the applied SOP. Recovery and viability of cells are largely unaffected by serum-free conditions even after overnight resting. Furthermore, one serum-free medium was identified that appears to enhance antigen-specific IFNγ-secretion
The environmental dependence of the stellar mass function at z ~ 1: Comparing cluster and field between the GCLASS and UltraVISTA surveys
Aims. We present the stellar mass functions (SMFs) of star-forming and quiescent galaxies from observations of ten rich, red-sequence selected, clusters in the Gemini Cluster Astrophysics Spectroscopic Survey (GCLASS) in the redshift range 0.86 < z < 1.34. We compare our results with field measurements at similar redshifts using data from a K_s-band selected catalogue of the COSMOS/UltraVISTA field.
Methods. We construct a K_s-band selected multi-colour catalogue for the clusters in eleven photometric bands covering u-8 μm, and estimate photometric redshifts and stellar masses using spectral energy distribution fitting techniques. To correct for interlopers in our cluster sample, we use the deep spectroscopic component of GCLASS, which contains spectra for 1282 identified cluster and field galaxies taken with Gemini/GMOS. This allowed us to correct cluster number counts from a photometric selection for false positive and false negative identifications. Both the photometric and spectroscopic samples are sufficiently deep that we can probe the SMF down to masses of 10^10 M_⊙.
Results. We distinguish between star-forming and quiescent galaxies using the rest-frame U − V versus V − J diagram, and find that the best-fitting Schechter parameters α and M∗ are similar within the uncertainties for these galaxy types within the different environments. However, there is a significant difference in the shape and normalisation of the total SMF between the clusters and the field sample. This difference in the total SMF is primarily a reflection of the increased fraction of quiescent galaxies in high-density environments. We apply a simple quenching model that includes components of mass- and environment-driven quenching, and find that in this picture 45^(+4)_(-3)% of the star-forming galaxies, which normally would be forming stars in the field, are quenched by the cluster.
Conclusions. If galaxies in clusters and the field quench their star formation via different mechanisms, these processes have to conspire in such a way that the shapes of the quiescent and star-forming SMF remain similar in these different environments
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