603 research outputs found
MegaMorph: classifying galaxy morphology using multi-wavelength S\'ersic profile fits
Aims. This work investigates the potential of using the wavelength-dependence
of galaxy structural parameters (S\'ersic index, n, and effective radius, Re)
to separate galaxies into distinct types. Methods. A sample of nearby galaxies
with reliable visual morphologies is considered, for which we measure
structural parameters by fitting multi-wavelength single-S\'ersic models.
Additionally, we use a set of artificially redshifted galaxies to test how
these classifiers behave when the signal-to-noise decreases. Results. We show
that the wavelength-dependence of n may be employed to separate
visually-classified early- and late-type galaxies, in a manner similar to the
use of colour and n. Furthermore, we find that the wavelength variation of n
can recover galaxies that are misclassified by these other morphological
proxies. Roughly half of the spiral galaxies that contaminate an early-type
sample selected using (u-r) versus n can be correctly identified as late-types
by N, the ratio of n measured in two different bands. Using a set of
artificially-redshifted images, we show that this technique remains effective
up to z ~ 0.1. N can therefore be used to achieve purer samples of early-types
and more complete samples of late-types than using a colour-n cut alone. We
also study the suitability of R, the ratio of Re in two different bands, as a
morphological classifier, but find that the average sizes of both early- and
late-type galaxies do not change substantially over optical wavelengths.Comment: 6 pages, 2 figures, 2 tables, Accepted for publication in A&
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
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
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
The importance of the local density in shaping the galaxy stellar mass functions
Exploiting the capabilities of four different surveys --- the
Padova-Millennium Galaxy and Group Catalogue (PM2GC), the WIde-field Nearby
Galaxy-cluster Survey (WINGS), the IMACS Cluster Building Survey (ICBS) and the
ESO Distant Cluster Survey (EDisCS) --- we analyze the galaxy stellar mass
distribution as a function of local density in mass-limited samples, in the
field and in clusters from low (z>0.04) to high (z<0.8) redshift. We find that
at all redshifts and in all environments, local density plays a role in shaping
the mass distribution. In the field, it regulates the shape of the mass
function at any mass above the mass limits. In clusters, it seems to be
important only at low masses (log M_ast/M_sun <10.1 in WINGS and log
M_ast/M_sun < 10.4 in EDisCS), otherwise it seems not to influence the mass
distribution. Putting together our results with those of Calvi et al. and
Vulcani et al. for the global environment, we argue that at least at local density is more important than global environment in determining the
galaxy stellar mass distribution, suggesting that galaxy properties are not
much dependent of halo mass, but do depend on local scale processes.Comment: MNRAS accepted, in pres
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