2,283 research outputs found
The Galaxy Population of Cluster RXJ0848+4453 at z=1.27
We present a study of the galaxy population in the cluster RXJ0848+4453 at
z=1.27, using deep HST NICMOS and WFPC2 images. We morphologically classify all
galaxies to K_s=20.6 that are covered by the HST imaging, and determine
photometric redshifts using deep ground based BRIzJK_s photometry. Of 22 likely
cluster members with morphological classifications, eleven (50%) are classified
as early-type galaxies, nine (41%) as spiral galaxies, and two (9%) as
``merger/peculiar''. At HST resolution the second brightest cluster galaxy is
resolved into a spectacular merger between three red galaxies of similar
luminosity, separated from each other by ~6 kpc, with an integrated magnitude
K=17.6 (~3 L* at z=1.27). The two most luminous early-type galaxies also show
evidence for recent or ongoing interactions. Mergers and interactions between
galaxies are possible because RXJ0848+4453 is not yet relaxed. The fraction of
early-type galaxies in our sample is similar to that in clusters at 0.5<z<1,
and consistent with a gradual decrease of the number of early-type galaxies in
clusters from z=0 to z=1.3. We find evidence that the color-magnitude relation
of the early-type galaxies is less steep than in the nearby Coma cluster. This
may indicate that the brightest early-type galaxies have young stellar
populations at z=1.27, but is also consistent with predictions of single age
``monolithic'' models with a galactic wind. The scatter in the color-magnitude
relation is ~0.04 in rest frame U-V, similar to that in clusters at 0<z<1.
Taken together, these results show that luminous early-type galaxies exist in
clusters at z~1.3, but that their number density may be smaller than in the
local Universe. Additional observations are needed to determine whether the
brightest early-type galaxies harbor young stellar populations.Comment: Accepted for publication in The Astrophysical Journal Letter
The Nascent Red Sequence at z~2
We present new constraints on the evolution of the early-type galaxy
color-magnitude relation (CMR) based on deep near-infrared imaging of a galaxy
protocluster at z=2.16 obtained using NICMOS on-board the Hubble Space
Telescope. This field contains a spectroscopically confirmed space-overdensity
of Lyman-alpha and H-alpha emitting galaxies which surrounds the powerful radio
galaxy MRC 1138-262. Using these NICMOS data we identify a significant
surface-overdensity (= 6.2x) of red J-H galaxies in the color-magnitude diagram
(when compared with deep NICMOS imaging from the HDF-N and UDF). The
optical-NIR colors of these prospective red-sequence galaxies indicate the
presence of on-going dust-obscured star-formation or recently formed (<~ 1.5
Gyr)stellar populations in a majority of the red galaxies. We measure the slope
and intrinsic scatter of the CMR for three different red galaxy samples
selected by a wide color cut, and using photometric redshifts both with and
without restrictions on rest-frame optical morphology. In all three cases both
the rest-frame slope and intrinsic color scatter are considerably higher
than corresponding values for lower redshift galaxy clusters. These results
suggest that while some relatively quiescent galaxies do exist in this
protocluster both the majority of the galaxy population and hence the
color-magnitude relation are still in the process of forming, as expected.Comment: 8 pages, 7 figures, accepted for publication in ApJ (to appear June
1, 2008, v679n2
Protoclusters associated with z > 2 radio galaxies. I. Characteristics of high redshift protoclusters
[Abridged] We present the results of a large program conducted with the Very
Large Telescope and Keck telescope to search for forming clusters of galaxies
near powerful radio galaxies at 2.0 < z < 5.2. We obtained narrow- and
broad-band images of nine radio galaxies and their surroundings. The imaging
was used to select candidate Lyman alpha emitting galaxies in ~3x3 Mpc^2 areas
near the radio galaxies. A total of 337 candidate emitters were found with a
rest-frame Lyman alpha equivalent width of EW_0 > 15 A and Sigma = EW_0/Delta
EW_0 > 3. Follow-up spectroscopy confirmed 168 Lyman alpha emitters near eight
radio galaxies. The success rate of our selection procedure is 91%. At least
six of our eight fields are overdense in Lyman alpha emitters by a factor 3-5.
Also, the emitters show significant clustering in velocity space. In the
overdense fields, the width of the velocity distributions of the emitters is a
factor 2-5 smaller than the width of the narrow-band filters. Taken together,
we conclude that we have discovered six forming clusters of galaxies
(protoclusters). We estimate that roughly 75% of powerful (L_2.7GHz > 10^33
erg/s/Hz/sr) high redshift radio galaxies reside in a protocluster, with a
sizes of at least 1.75 Mpc. We estimate that the protoclusters have masses in
the range 2-9 x 10^14 Msun and they are likely to be progenitors of present-day
(massive) clusters of galaxies. For the first time, we have been able to
estimate the velocity dispersion of cluster progenitors from z~5 to ~2. The
velocity dispersion of the emitters increases with cosmic time, in agreement
with the dark matter velocity dispersion in numerical simulations of forming
massive clusters.Comment: 30 pages, 20 figures. Published in A&A. The article with high
resolution figures is available at
http://www.ast.cam.ac.uk/~venemans/research/datapaper/index.htm
The Evolution of Early-Type Galaxies in Distant Clusters
We present results from an optical-IR photometric study of early-type
galaxies in 19 galaxy clusters out to z=0.9. The galaxy sample is selected on
the basis of morphologies determined from HST WFPC2 images, and is
photometrically defined in the K-band to minimize redshift-dependent selection
biases. The optical-IR colors of the early-type cluster galaxies become bluer
with increasing redshift in a manner consistent with the passive evolution of
an old stellar population formed at an early cosmic epoch. The degree of color
evolution is similar for clusters at similar redshift, and does not depend
strongly on the optical richness or X-ray luminosity of the cluster, suggesting
that the history of early-type galaxies is relatively insensitive to
environment. The slope of the color-magnitude relationship shows no significant
change out to z=0.9, providing evidence that it arises from a correlation
between galaxy mass and metallicity, not age. Finally, the intrinsic scatter in
the optical-IR colors is small and nearly constant with redshift, indicating
that the majority of giant, early-type galaxies in clusters share a common star
formation history, with little perturbation due to uncorrelated episodes of
later star formation. Taken together, our results are consistent with models in
which most early-type galaxies in rich clusters are old, formed the majority of
their stars at high redshift in a well-synchronized fashion, and evolved
quiescently thereafter.Comment: 55 pages, 24 figures, uses AASTeX. Accepted for publication in The
Astrophysical Journa
Scaling Relations and Overabundance of Massive Clusters at z>~1 from Weak-Lensing Studies with HST
We present weak gravitational lensing analysis of 22 high-redshift (z >~1)
clusters based on Hubble Space Telescope images. Most clusters in our sample
provide significant lensing signals and are well detected in their
reconstructed two-dimensional mass maps. Combining the current results and our
previous weak-lensing studies of five other high-z clusters, we compare
gravitational lensing masses of these clusters with other observables. We
revisit the question whether the presence of the most massive clusters in our
sample is in tension with the current LambdaCDM structure formation paradigm.
We find that the lensing masses are tightly correlated with the gas
temperatures and establish, for the first time, the lensing mass-temperature
relation at z >~ 1. For the power law slope of the M-TX relation (M propto
T^{\alpha}), we obtain \alpha=1.54 +/- 0.23. This is consistent with the
theoretical self-similar prediction \alpha=3/2 and with the results previously
reported in the literature for much lower redshift samples. However, our
normalization is lower than the previous results by 20-30%, indicating that the
normalization in the M-TX relation might evolve. After correcting for Eddington
bias and updating the discovery area with a more conservative choice, we find
that the existence of the most massive clusters in our sample still provides a
tension with the current Lambda CDM model. The combined probability of finding
the four most massive clusters in this sample after marginalization over
current cosmological parameters is less than 1%.Comment: ApJ in press. See http://www.supernova.lbl.gov for additional
information pertaining to the HST Cluster SN Surve
Effect of rejection on electrophysiologic function of canine intestinal grafts: Correlation with histopathology and na-k-ATPase activity
To investigate whether electrophysiologic changes can detect the early onset and progress of intestinal rejection, changes in in vitro electrophysiologic function, intestinal histopathology, and Na-K-ATPase activity were studied in dogs. Adult mongrel dogs of both sexes, weighing 18-24 kg, were used for auto and allo small bowel transplantation. The entire small bowels, except for short segments at the proximal and distal ends, were snitched between a pair of dogs (allograft). Animals receiving intestinal autotransplantation were used as controls. AIIograji recipients were sacrificed 3, 4, 5, 7, or 9 days after transplantation, and autograft recipients were sacrificed 3, 7, or 14 days afier transplantation. Immunosuppression was not used. Electrophysiologic measurements were done with an Ussing chamber. Histological analysis was performed blindly using whole thickness sections. Na-K-ATPase activity in the mucosal tissue, which is said to regulate the potential difference, was also measured. Potential difference, resistance, and Na-K-ATPase activity of the allografi intestine decreased with time and were significantly lower 7 and 9 days after transplantation compared to host intestine, normul intestine, and graft intestine of controls (autograft). Potential difference, resistance, and Na-K-ATPase activity of the native intestinal tissue and the autografts did not decrease with time. Detection of histologically mild rejection of the intestine, which is important for appropriate immunosup-pressive treatment in clinical cases, could not be achieved based on electrophysiology or Na-K-ATPase activity. Deterioration of electrophysiologic function during rejection correlated with the histological rejection process and Na-K-ATPase activity; however, electrophysiology my not be a reliable tool for monitoring grafrs, since it cannot detect early intestinal rejection. © 1995 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted
Barred Galaxies in the Coma Cluster
We use ACS data from the HST Treasury survey of the Coma cluster (z~0.02) to
study the properties of barred galaxies in the Coma core, the densest
environment in the nearby Universe. This study provides a complementary data
point for studies of barred galaxies as a function of redshift and environment.
From ~470 cluster members brighter than M_I = -11 mag, we select a sample of
46 disk galaxies (S0--Im) based on visual classification. The sample is
dominated by S0s for which we find an optical bar fraction of 47+/-11% through
ellipse fitting and visual inspection. Among the bars in the core of the Coma
cluster, we do not find any very large (a_bar > 2 kpc) bars. Comparison to
other studies reveals that while the optical bar fraction for S0s shows only a
modest variation across low-to-intermediate density environments (field to
intermediate-density clusters), it can be higher by up to a factor of ~2 in the
very high-density environment of the rich Coma cluster core.Comment: Proceedings of the Bash symposium, to appear in the Astronomical
Society of the Pacific Conference Series, eds. L. Stanford, L. Hao, Y. Mao,
J. Gree
Increased operant responding for ethanol in male C57BL/6J mice: specific regulation by the ERK1/2, but not JNK, MAP kinase pathway
Extracellular signal-regulated protein kinase (ERK1/2) is a member of the mitogen-activated protein kinase (MAPK) signaling pathway and a key molecular target for ethanol (EtOH) and other drugs of abuse
Constructing a WISE High Resolution Galaxy Atlas
After eight months of continuous observations, the Wide-field Infrared Survey
Explorer (WISE) mapped the entire sky at 3.4 {\mu}m, 4.6 {\mu}m, 12 {\mu}m and
22 {\mu}m. We have begun a dedicated WISE High Resolution Galaxy Atlas (WHRGA)
project to fully characterize large, nearby galaxies and produce a legacy image
atlas and source catalogue. Here we summarize the deconvolution technique used
to significantly improve the spatial resolution of WISE imaging, specifically
designed to study the internal anatomy of nearby galaxies. As a case study, we
present results for the galaxy NGC 1566, comparing the WISE super-resolution
image processing to that of Spitzer, GALEX and ground-based imaging. The is the
first paper in a two part series; results for a much larger sample of nearby
galaxies is presented in the second paper.Comment: Published in the AJ (2012, AJ, 144, 68
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