263 research outputs found
Environmental dependence of polycyclic aromatic hydrocarbon emission at z~0.8. Investigation by observing the RX J0152.7-1357 with AKARI
We study the environmental dependence of the strength of polycyclic aromatic
hydrocarbon (PAH) emission by AKARI observations of RX J0152.7-1357, a galaxy
cluster at z=0.84. PAH emission reflects the physical conditions of galaxies
and dominates 8 um luminosity (L8), which can directly be measured with the L15
band of AKARI. L8 to infrared luminosity (LIR) ratio is used as a tracer of the
PAH strength. Both photometric and spectroscopic redshifts are applied to
identify the cluster members. The L15-band-detected galaxies tend to reside in
the outskirt of the cluster and have optically green colour, R-z'~ 1.2. We find
no clear difference of the L8/LIR behaviour of galaxies in field and cluster
environment. The L8/LIR of cluster galaxies decreases with
specific-star-formation rate divided by that of main-sequence galaxies, and
with LIR, consistent with the results for field galaxies. The relation between
L8/LIR and LIR is between those at z=0 and z=2 in the literature. Our data also
shows that starburst galaxies, which have lower L8/LIR than main-sequence, are
located only in the outskirt of the cluster. All these findings extend previous
studies, indicating that environment affects only the fraction of galaxy types
and does not affect the L8/LIR behaviour of star-forming galaxies.Comment: 8 pages, 7 figures. Accepted for Publication in A&
Dependence of the Build-up of the Colour-Magnitude Relation on Cluster Richness at z ~ 0.8
We present environmental dependence of the build-up of the colour-magnitude
relation (CMR) at z ~ 0.8. It is well established that massive early-type
galaxies exhibit a tight CMR in clusters up to at least z ~ 1. The faint end of
the relation, however, has been much less explored especially at high redshifts
primarily due to limited depths of the data. Some recent papers have reported a
deficit of the faint red galaxies on the CMR at 0.8 < z < 1, but this has not
been well confirmed yet and is still controversial. Using a deep, multi-colour,
panoramic imaging data set of the distant cluster RXJ1716.4+6708 at z=0.81,
newly taken with the Prime Focus Camera (Suprime-Cam) on the Subaru Telescope,
we carry out an analysis of faint red galaxies with a care for incompleteness.
We find that there is a sharp decline in the number of red galaxies toward the
faint end of the CMR below M*+2. We compare our result with those for other
clusters at z ~ 0.8 taken from the literature, which show or do not show the
deficit. We suggest that the "deficit" of faint red galaxies is dependent on
the richness or mass of the clusters, in the sense that poorer systems show
stronger deficits. This indicates that the evolutionary stage of less massive
galaxies depends critically on environment.Comment: 11 pages, 10 figures, accepted for publication in MNRA
Discovery of a Strongly Lensed Galaxy at z=3.9 behind a z=0.83 Galaxy Cluster
We report the discovery and spectroscopic confirmation of three
gravitationally-lensed images of a galaxy at z=3.9 in the background of a
distant, rich cluster of galaxies at z=0.83, on the basis of observations with
Faint Object Camera And Spectrograph (FOCAS) on the Subaru telescope. We
construct a simple lens model of the cluster mass distribution based on Jee et
al.'s weak lensing mass estimates from deep, high-resolution images by Advanced
Camera for Surveys (ACS) on the Hubble Space Telescope. The lens model can
account simultaneously for the observed image configuration and the flux ratio
of the closer pair located close to the critical curve. The parities of the
three images are also consistent with the lensing hypothesis. Since this galaxy
is apparently bright (i'_{AB} \sim 23.7) for its redshift due to the
magnification, it serves as a good high redshift target on which we can make
extensive and detailed studies based on multi-wavelength imaging and
spectroscopy.Comment: 4 pages, 3 figures, 1 table, accepted for publication in PAS
A Deficit of Faint Red Galaxies in the Possible Large-Scale Structures around the RDCS J1252.9-2927 Cluster at z=1.24
(Abridged) We report a discovery of possible large-scale structures around
the RDCS J1252.9-2927 cluster at z=1.24 based on photometric redshifts. We
carried out multi-band wide-field imaging with Suprime-Cam on the Subaru
Telescope and WFCAM on the United Kingdom Infra-Red Telescope (UKIRT). The
distribution of photo-z selected galaxies reveals clumpy structures surrounding
the central cluster. We compare the observed structure with an X-ray map and
find that two of the four plausible clumps show significant X-ray emissions and
one with a marginal detection, which strongly suggest that they are dynamically
bound systems. Following the discovery of the possible large-scale structure,
we carried out deeper SOFI K_s-band imaging with New Technology Telescope on
the four plausible clumps. We construct the optical-to-near-infrared
colour-magnitude diagrams of the galaxies in the clumps, and find that the
colour-magnitude relation (CMR) of the red galaxies in the clumps is sharply
truncated below K_s=22. Interestingly, the main cluster shows a clear relation
down to K_s=23 (Lidman et al. 2004). We suggest that galaxies follow the
'environment-dependent down-sizing' evolution. Massive galaxies in high density
environments first stop forming stars and become red. Less massive galaxies in
less dense environments become red at later times. Based on a few assumptions,
we predict that the brightest tip of the CMR appears at z~2.5.Comment: 10 pages, 8 figures, accepted for publication in MNRA
On the formation time scale of massive cluster ellipticals based on deep near-IR spectroscopy at z~2
We present improved constraints on the formation time scale of massive
cluster galaxies based on rest-frame optical spectra of galaxies in a forming
cluster located at z=2.16. The spectra are obtained with MOIRCS on the Subaru
telescope with an integration time of ~7 hours. We achieve accurate redshift
measurements by fitting SEDs using the spectra and broad-band photometry
simultaneously, allowing us to identify probable cluster members. Clusters at
low redshifts are dominated by quiescent galaxies, but we find that quiescent
galaxies and star forming galaxies co-exist in this z=2 system. Interestingly,
the quiescent galaxies form a weak red sequence in the process of forming. By
stacking the spectra of star forming galaxies, we observe strong emission lines
such as [OII] and [OIII] and we obtain a tentative hint of AGN activities in
these galaxies. On the other hand, the stacked spectrum of the quiescent
galaxies reveals a clear 4000A break with a possible CaII H+K absorption
feature and strong emission lines such as [OII] are absent in the spectrum,
confirming the quiescent nature of these galaxies. We then perform detailed
spectral analyses of the stacked spectrum, which suggest that these massive
quiescent galaxies formed at redshifts between 3 and 4 on a time scale of <~0.5
Gyr. This short formation time scale is not reproduced in recent numerical
simulations. We discuss possible mechanisms for how these galaxies form 10^11
Msun stellar mass on a short time scale and become red and quiescent by z=2.Comment: 17 pages, 14 figures, accepted for publication in Ap
The Number Density of Old Passively-Evolving Galaxies at z=1 in the Subaru/XMM-Newton Deep Survey Field
We obtained the number counts and the rest-frame B-band luminosity function
of the color-selected old passively-evolving galaxies (OPEGs) at z=1 with very
high statistical accuracy using a large and homogeneous sample of about 4000
such objects with z' <25 detected in the area of 1.03 deg^2 in the
Subaru/XMM-Newton Deep Survey (SXDS) field. Our selection criteria are defined
on the i'-z' and R-z' color-magnitude plane so that OPEGs at z=0.9-1.1 with
formation redshift z_f=2-10 are properly sampled. The limiting magnitude
corresponds to the luminosity of galaxies with M_*+3 at z=0. We made a pilot
redshift observations for 99 OPEG candidates with 19 < z' < 22 and found that
at least 78% (73/93) of the entire sample, or 95% (73/77) of these whose
redshifts were obtained are indeed lie between z=0.87 and 1.12 and the most of
their spectra show the continuum break and strong Ca H and K lines, indicating
that these objects are indeed dominated by the old stellar populations. We then
compare our results with the luminosity functions of the color- or the
morphologically-selected early type galaxies at z=0 taking the evolutionary
factor into account and found that the number density of old passive galaxies
with sim M_* magnitude at z~1 averaged over the SXDS area is 40-60% of the
equivalently red galaxies and 60-85% of the morphologically-selected E/S0
galaxies at z=0 depending on their luminosity evolution. It is revealed that
more than half, but not all, of the present-day early-type galaxies had already
been formed into quiescent passive galaxies at z=1.Comment: 28 pages, accepted for publication in Astrophysical Journal. The full
version of the paper including Fig.3 and Fig.4 (large size) in full
resolution is put at
http://optik2.mtk.nao.ac.jp/~yamada/astronomy/sxdsred.htm
Star formation in the cluster CLG0218.3-0510 at z=1.62 and its large-scale environment: the infrared perspective
The galaxy cluster CLG0218.3-0510 at z=1.62 is one of the most distant galaxy
clusters known, with a rich muti-wavelength data set that confirms a mature
galaxy population already in place. Using very deep, wide area (20x20 Mpc)
imaging by Spitzer/MIPS at 24um, in conjunction with Herschel 5-band imaging
from 100-500um, we investigate the dust-obscured, star-formation properties in
the cluster and its associated large scale environment. Our galaxy sample of
693 galaxies at z=1.62 detected at 24um (10 spectroscopic and 683 photo-z)
includes both cluster galaxies (i.e. within r <1 Mpc projected clustercentric
radius) and field galaxies, defined as the region beyond a radius of 3 Mpc. The
star-formation rates (SFRs) derived from the measured infrared luminosity range
from 18 to 2500 Ms/yr, with a median of 55 Ms/yr, over the entire radial range
(10 Mpc). The cluster brightest FIR galaxy, taken as the centre of the galaxy
system, is vigorously forming stars at a rate of 25670 Ms/yr, and the
total cluster SFR enclosed in a circle of 1 Mpc is 116196 Ms/yr. We
estimate a dust extinction of about 3 magnitudes by comparing the SFRs derived
from [OII] luminosity with the ones computed from the 24um fluxes. We find that
the in-falling region (1-3 Mpc) is special: there is a significant decrement
(3.5x) of passive relative to star-forming galaxies in this region, and the
total SFR of the galaxies located in this region is lower (130 Ms/yr/Mpc2) than
anywhere in the cluster or field, regardless of their stellar mass. In a
complementary approach we compute the local galaxy density, Sigma5, and find no
trend between SFR and Sigma5. However, we measure an excess of star-forming
galaxies in the cluster relative to the field by a factor 1.7, that lends
support to a reversal of the SF-density relation in CLG0218.Comment: accepted for publication in MNRAS. v2: minor correction
N-Cadherin Expressed on Malignant T Cell Lymphoma Cells is Functional, and Promotes Heterotypic Adhesion Between the Lymphoma Cells and Mesenchymal Cells Expressing N-Cadherin
Cadherins are Ca2+-dependent cell–cell adhesion molecules, and are involved in the formation and maintenance of the organocellular architecture. Using a combination of molecular biologic and biochemical methods, we analyzed cadherins expressed on cultured human malignant lymphoma cell lines (adult T cell lymphomas, human T cell leukemia virus type 1-negative T cell lines, and thymus-derived lymphoma cell lines), and obtained evidence that N-cadherin is the major cadherin expressed on these cells. These cells were found to form cell aggregates in a Ca2+-dependent manner, and more importantly to coaggregate and adhere with cells expressing N-cadherin, suggesting that N-cadherin on lymphoma cells is functionally active. Therefore, N-cadherin expressed on lymphoma cells could underlie the frequent invasion of these cells into the mesenchymal tissue in the skin and the central nervous system
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