83 research outputs found
Color and Morphology of Galaxies in the Region of the 3C 324 Clusters at z 1.2
We investigated the color and morphology of optically selected galaxies in
the region of clusters at z 1.2 near to the radio galaxy 3C 324 using
archived data taken with the Hubble Space Telescope. The faint galaxies
selected at the HST F702W band that contribute to the surface-density excess of
the region have wide ranges of color, size, and morphology, which are not
likely to be due to contamination by foreground galaxies. Namely, the
rest-frame ultraviolet emission properties of the galaxies in the clusters are
not very homogeneous; various amounts of star-formation activity may occur in a
significant fraction of them. Although our analysis is purely statistical, we
find that typical star-forming galaxies with blue colors have a relatively
late-type morphology compared to the red quiescent population in the systems.Comment: 12 pages, 10 figures, accepted for publication in PAS
Central Concentration of Asymmetric Features in Post-starburst Galaxies at
We present morphological analyses of Post-starburst galaxies (PSBs) at
in the COSMOS field. We fitted ultraviolet to mid-infrared
multi-band photometry of objects with from COSMOS2020 catalogue with
population synthesis models assuming non-parametric, piece-wise constant
function of star formation history, and selected 94 those galaxies that have
high specific star formation rates (SSFRs) of more than yr
in 321--1000 Myr before observation and an order of magnitude lower SSFRs
within recent 321 Myr. We devised a new non-parametric morphological index
which quantifies concentration of asymmetric features, , and measured it
as well as concentration and asymmetry on the Hubble Space
Telescope/Advanced Camera for Surveys -band images. While
relatively high and low values of PSBs are similar with those of
quiescent galaxies rather than star-forming galaxies, we found that PSBs show
systematically higher values of than both quiescent and star-forming
galaxies; 36% of PSBs have , while only 16% (2%) of
quiescent (star-forming) galaxies show such high values. Those PSBs
with high have relatively low overall asymmetry of , but
show remarkable asymmetric features near the centre. The fraction of those PSBs
with high increases with increasing SSFR in 321--1000 Myr before
observation rather than residual on-going star formation. These results and
their high surface stellar mass densities suggest that those galaxies
experienced a nuclear starburst in the recent past, and processes that cause
such starbursts could lead to the quenching of star formation through rapid gas
consumption, supernova/AGN feedback, and so on.Comment: 18 pages, 17 figures, accepted for publication in MNRA
Subaru Weak-Lensing Survey of Dark Matter Subhalos in the Coma Cluster : Subhalo Mass Function and Statistical Properties
We present a 4 deg^2 weak gravitational lensing survey of subhalos in the
very nearby Coma cluster using the Subaru/Suprime-Cam. The large apparent size
of cluster subhalos allows us to measure the mass of 32 subhalos detected in a
model-independent manner, down to the order of 10^-3 of the virial mass of the
cluster. Weak-lensing mass measurements of these shear-selected subhalos enable
us to investigate subhalo properties and the correlation between subhalo masses
and galaxy luminosities for the first time. The mean distortion profiles
stacked over subhalos show a sharply truncated feature which is well-fitted by
a Navarro-Frenk-White (NFW) mass model with the truncation radius, as expected
due to tidal destruction by the main cluster. We also found that subhalo
masses, truncation radii, and mass-to-light ratios decrease toward the cluster
center. The subhalo mass function, dn/dln M_sub, in the range of 2 orders of
magnitude in mass, is well described by a single power law or a Schechter
function. Best-fit power indices of 1.09_-0.32^+0.42 for the former model and
0.99_-0.23^+0.34 for the latter, are in remarkable agreement with slopes of
~0.9-1.0 predicted by the cold dark matter paradigm. The tangential distortion
signals in the radial range of 0.02-2Mpc/h from the cluster center show a
complex structure which is well described by a composition of three mass
components of subhalos, the NFW mass distribution as a smooth component of the
main cluster, and a lensing model from a large scale structure behind the
cluster. Although the lensing signals are 1 order of magnitude lower than those
for clusters at z~0.2, the total signal-to-noise ratio, S/N=13.3, is comparable
to, or higher, because the enormous number of background source galaxies
compensates for the low lensing efficiency of the low lensing efficiency of the
nearby cluster.Comment: 30 pages, 18 figures, 9 tables, ApJ in press. Full resolution version
is available at http://www.asiaa.sinica.edu.tw/~okabe/files/coma_survey.pd
Proto-Clusters with Evolved Populations around Radio Galaxies at z~2.5
We report a discovery of proto-cluster candidates around high redshift radio
galaxies at z~2.5 on the basis of clear statistical excess of colour-selected
galaxies around them seen in the deep near-infrared imaging data obtained with
CISCO on Subaru Telescope. We have observed six targets, all at similar
redshifts at z~2.5, and our data reach to J=23.5, H=22.6 and K=21.8 (5 sigma)
and cover a 1.6' x 1.6' field centered on each radio galaxy. We apply colour
cuts in JHKs in order to exclusively search for galaxies located at high
redshifts, z>2. Over the magnitude range of 19.5<K<21.5 we see a significant
excess of red galaxies with J-K>2.3 by a factor of two around the combined
radio galaxies fields compared to those found in the general field of GOODS
South. The excess of galaxies around the radio galaxies fields becomes more
than factor of three around 19.5<K<20.5 when the two-colours cuts are applied
with JHKs. Such overdensity of the colour-selected galaxies suggest that those
fields tend to host high density regions at high redshifts, although there
seems to be the variety of the density of the colour-selected galaxies in each
field. In particular, two radio galaxies fields out of the six observed fields
show very strong density excess and these are likely to be proto-clusters
associated to the radio galaxies which would evolve into rich clusters of
galaxies dominated by old passively evolving galaxies.Comment: 7 pages, 4 figures, accepted for publication in MNRA
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