217 research outputs found
Mapping the spatial distribution of star formation in cluster galaxies at z ~ 0.5 with the Grism Lens-Amplified Survey from Space (GLASS)
We present the first study of the spatial distribution of star formation in z ~ 0.5 cluster galaxies. The analysis is based on data taken with the Wide Field Camera 3 as part of the Grism Lens-Amplified Survey from Space (GLASS). We illustrate the methodology by focusing on two clusters (MACS0717.5+3745 and MACS1423.8+2404) with different morphologies (one relaxed and one merging) and use foreground and background galaxies as field control sample. The cluster+field sample consists of 42 galaxies with stellar masses in the range 108-1011 M ☉, and star formation rates in the range 1-20 M☉ yr -1. In both environments, Hα is more extended than the rest-frame UV continuum in 60% of the cases, consistent with diffuse star formation and inside out growth. The Hα emission appears more extended in cluster galaxies than in the field, pointing perhaps to ionized gas being stripped and/or star formation being enhanced at large radii. The peak of the Hα emission and that of the continuum are offset by less than 1 kpc. We investigate trends with the hot gas density as traced by the X-ray emission, and with the surface mass density as inferred from gravitational lens models and find no conclusive results. The diversity of morphologies and sizes observed in Hα illustrates the complexity of the environmental process that regulate star formation
GASP IV: A muse view of extreme ram-pressure stripping in the plane of the sky: the case of jellyfish galaxy JO204
In the context of the GAs Stripping Phenomena in galaxies with Muse (GASP)
survey, we present the characterization of JO204, a jellyfish galaxy in A957, a
relatively low-mass cluster with . This galaxy
shows a tail of ionized gas that extends up to 30 kpc from the main body in the
opposite direction of the cluster center. No gas emission is detected in the
galaxy outer disk, suggesting that gas stripping is proceeding outside-in. The
stellar component is distributed as a regular disk galaxy; the stellar
kinematics shows a symmetric rotation curve with a maximum radial velocity of
200km/s out to 20 kpc from the galaxy center. The radial velocity of the gas
component in the central part of the disk follows the distribution of the
stellar component; the gas kinematics in the tail retains the rotation of the
galaxy disk, indicating that JO204 is moving at high speed in the intracluster
medium. Both the emission and radial velocity maps of the gas and stellar
components indicate ram-pressure as the most likely primary mechanism for gas
stripping, as expected given that JO204 is close to the cluster center and it
is likely at the first infall in the cluster. The spatially resolved star
formation history of JO204 provides evidence that the onset of ram-pressure
stripping occurred in the last 500 Myr, quenching the star formation activity
in the outer disk, where the gas has been already completely stripped. Our
conclusions are supported by a set of hydrodynamic simulations.Comment: accepted for publication in Ap
Characterization and modeling of contamination for Lyman break galaxy samples at high redshift
The selection of high redshift sources from broad-band photometry using the
Lyman-break galaxy (LBG) technique is a well established methodology, but the
characterization of its contamination for the faintest sources is still
incomplete. We use the optical and near-IR data from four (ultra)deep Hubble
Space Telescope legacy fields to investigate the contamination fraction of LBG
samples at z~5-8 selected using a colour-colour method. Our approach is based
on characterizing the number count distribution of interloper sources, that is
galaxies with colors similar to those of LBGs, but showing detection at
wavelengths shorter than the spectral break. Without sufficient sensitivity at
bluer wavelengths, a subset of interlopers may not be properly classified, and
contaminate the LBG selection. The surface density of interlopers in the sky
gets steeper with increasing redshift of LBG selections. Since the intrinsic
number of dropouts decreases significantly with increasing redshift, this
implies increasing contamination from misclassified interlopers with increasing
redshift, primarily by intermediate redshift sources with unremarkable
properties (intermediate ages, lack of ongoing star formation and low/moderate
dust content). Using Monte Carlo simulations, we estimate that the CANDELS deep
data have contamination induced by photometric scatter increasing from ~2% at
z~5 to ~6% at z~8 for a typical dropout color >1 mag, with contamination
naturally decreasing for a more stringent dropout selection. Contaminants are
expected to be located preferentially near the detection limit of surveys,
ranging from 0.1 to 0.4 contaminants per arcmin2 at J=30, depending on the
field considered. This analysis suggests that the impact of contamination in
future studies of z>10 galaxies needs to be carefully considered.Comment: 17 pages, 13 figures, ApJ in pres
From blue star-forming to red passive: galaxies in transition in different environments
Exploiting a mass complete (M_*>10^(10.25)M_sun) sample at 0.03<z<0.11 drawn
from the Padova Millennium Galaxy Group Catalog (PM2GC), we use the (U-B)_rf
color and morphologies to characterize galaxies, in particular those that show
signs of an ongoing or recent transformation of their star formation activity
and/or morphology - green galaxies, red passive late types, and blue
star-forming early types. Color fractions depend on mass and only for
M_*<10^(10.7)M_sun on environment. The incidence of red galaxies increases with
increasing mass, and, for M_*<10^(10.7)M_sun, decreases toward the group
outskirts and in binary and single galaxies. The relative abundance of green
and blue galaxies is independent of environment, and increases monotonically
with galaxy mass. We also inspect galaxy structural parameters, star-formation
properties, histories and ages and propose an evolutionary scenario for the
different subpopulations. Color transformations are due to a reduction and
suppression of SFR in both bulges and disks which does not noticeably affect
galaxy structure. Morphological transitions are linked to an enhanced
bulge-to-disk ratio due to the removal of the disk, not to an increase of the
bulge. Our modeling suggests that green colors might be due to star formation
histories declining with long timescales, as an alternative scenario to the
classical "quenching" processes. Our results suggest that galaxy
transformations in star formation activity and morphology depend neither on
environment nor on being a satellite or the most massive galaxy of a halo. The
only environmental dependence we find is the higher fast quenching efficiency
in groups giving origin to post-starburst signatures.Comment: 20 pages, 12 figures, accepted for publication in Ap
The star formation history of galaxies: the role of galaxy mass, morphology and environment
We analyze the star formation history (SFH) of galaxies as a function of
present-day environment, galaxy stellar mass and morphology. The SFH is derived
by means of a non-parametric spectrophotometric model applied to individual
galaxies at z ~ 0.04- 0.1 in the WINGS clusters and the PM2GC field. The field
reconstructed evolution of the star formation rate density (SFRD) follows the
values observed at each redshift (Madau & Dickinson 2014), except at z > 2
where our estimate is ~ 1.7x higher than the high-z observed value. The slope
of the SFRD decline with time gets progressively steeper going from low mass to
high mass haloes. The decrease of the SFRD since z = 2 is due to 1) quenching -
50% of the SFRD in the field and 75% in clusters at z > 2 originated in
galaxies that are passive today - and 2) the fact that the average SFR of
today's star-forming galaxies has decreased with time. We quantify the
contribution to the SFRD(z) of galaxies of today's different masses and
morphologies. The current morphology correlates with the current star formation
activity but is irrelevant for the past stellar history. The average SFH
depends on galaxy mass, but galaxies of a given mass have different histories
depending on their environment. We conclude that the variation of the SFRD(z)
with environment is not driven by different distributions of galaxy masses and
morphologies in clusters and field, and must be due to an accelerated formation
in high mass haloes compared to low mass ones even for galaxies that will end
up having the same galaxy mass today.Comment: 16 pages, 10 figures. Published on MNRA
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