288 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&
The concentration-mass relation of clusters of galaxies from the OmegaWINGS survey
The relation between a cosmological halo concentration and its mass (cMr) is
a powerful tool to constrain cosmological models of halo formation and
evolution. On the scale of galaxy clusters the cMr has so far been determined
mostly with X-ray and gravitational lensing data. The use of independent
techniques is helpful in assessing possible systematics. Here we provide one of
the few determinations of the cMr by the dynamical analysis of the
projected-phase-space distribution of cluster members. Based on the WINGS and
OmegaWINGS data sets, we used the Jeans analysis with the MAMPOSSt technique to
determine masses and concentrations for 49 nearby clusters, each of which has
~60 spectroscopic members or more within the virial region, after removal of
substructures. Our cMr is in statistical agreement with theoretical predictions
based on LambdaCDM cosmological simulations. Our cMr is different from most
previous observational determinations because of its flatter slope and lower
normalization. It is however in agreement with two recent cMr obtained using
the lensing technique on the CLASH and LoCuSS cluster data sets. In the future
we will extend our analysis to galaxy systems of lower mass and at higher
redshifts.Comment: Astronomy & Astrophysics in press. 11 pages, 6 figure
The Grism Lens-Amplified Survey from Space (GLASS). XII. Spatially Resolved Galaxy Star Formation Histories and True Evolutionary Paths at z > 1
Modern data empower observers to describe galaxies as the spatially and
biographically complex objects they are. We illustrate this through case
studies of four, systems based on deep, spatially resolved, 17-band
+ G102 + G141 Hubble Space Telescope grism spectrophotometry. Using full
spectrum rest-UV/-optical continuum fitting, we characterize these galaxies'
observed kpc-scale structures and star formation rates (SFRs) and
reconstruct their history over the age of the universe. The sample's
diversity---passive to vigorously starforming; stellar masses to ---enables us to draw spatio-temporal inferences
relevant to key areas of parameter space (Milky Way- to super-Andromeda-mass
progenitors). Specifically, we find signs that bulge mass-fractions () and
SF history shapes/spatial uniformity are linked, such that higher s
correlate with "inside-out growth" and central specific SFRs that peaked above
the global average for all starforming galaxies at that epoch. Conversely, the
system with the lowest had a flat, spatially uniform SFH with normal peak
activity. Both findings are consistent with models positing a feedback-driven
connection between bulge formation and the switch from rising to falling SFRs
("quenching"). While sample size forces this conclusion to remain tentative,
this work provides a proof-of-concept for future efforts to refine or refute
it: JWST, WFIRST, and the 30-m class telescopes will routinely produce data
amenable to this and more sophisticated analyses. These samples---spanning
representative mass, redshift, SFR, and environmental regimes---will be ripe
for converting into thousands of sub-galactic-scale empirical windows on what
individual systems actually looked like in the past, ushering in a new dialog
between observation and theory.Comment: 18 pp, 15 figs, 3 tables (main text); 5 pp, 5 figs, 1 table
(appendix); Submitted to AAS Journals 1 October 201
The morphological transformation of ram pressure stripped galaxies: a pathway from late to early galaxy types
We investigate how the ageing of stellar populations can drive a
morphological transformation in galaxies whose star formation (SF) activity has
been quenched on short timescales, like in cluster galaxies subject to ram
pressure stripping from the intracluster medium. For this purpose, we use a
sample of 91 galaxies with MUSE data from the GASP program and of their
spatially resolved SF history derived with the spectral modelling software
SINOPSIS. We simulate the future continuation of the SF activities by exploring
two quenching scenarios: an instantaneous truncation of the SF across the whole
disc, and an outside-in quenching with typical stripping timescales of 0.5 Gyr
and 1 Gyr. For each scenario we produce mock MUSE spectroscopic datacubes and
optical images for our galaxies during their evolution, and classify their
morphology using a new diagnostic tool, calibrated on cluster galaxies from the
OmegaWINGS Survey. We find that, in all scenarios considered, the initial
galaxy population dominated by blue-cloud spirals (90%) evolves into a mixed
population mostly composed by red-sequence spirals (50-55%) and lenticulars
(~40%). The morphology transformation is completed after just 1.5-3.5 Gyr,
proceeding faster in more efficient quenching scenarios. Our results indicate
that, even without accounting for dynamical processes, SF quenching caused by
the harsh environment of a cluster can significantly affect the morphology of
the infalling galaxy population on timescales of a few Gyr.Comment: 19 pages, 11 figures, accepted for publication in MNRA
GASP XVIII: Star formation quenching due to AGN feedback in the central region of a jellyfish galaxy
We report evidence for star formation quenching in the central 8.6 kpc region
of the jellyfish galaxy JO201 which hosts an active galactic nucleus, while
undergoing strong ram pressure stripping. The ultraviolet imaging data of the
galaxy disk reveal a region with reduced flux around the center of the galaxy
and a horse shoe shaped region with enhanced flux in the outer disk. The
characterization of the ionization regions based on emission line diagnostic
diagrams shows that the region of reduced flux seen in the ultraviolet is
within the AGN-dominated area. The CO J map of the galaxy disk reveals
a cavity in the central region. The image of the galaxy disk at redder
wavelengths (9050-9250 \overset{\lower.5em\circ}{\mathrm{A}}) reveals the
presence of a stellar bar. The star formation rate map of the galaxy disk shows
that the star formation suppression in the cavity occurred in the last few
10 yr. We present several lines of evidence supporting the scenario that
suppression of star formation in the central region of the disk is most likely
due to the feedback from the AGN. The observations reported here make JO201 a
unique case of AGN feedback and environmental effects suppressing star
formation in a spiral galaxy.Comment: Author's accepted manuscrip
Multi-wavelength structure analysis of local cluster galaxies: The WINGS project
© ESO 2020. We present a multi-wavelength analysis of the galaxies in nine clusters selected from the WINGS dataset, examining how galaxy structure varies as a function of wavelength and environment using the state of the art software GALAPAGOS-2. We simultaneously fit single-Sérsic functions on three optical (u, B and V) and two near-infrared (J and K) bands thus creating a wavelength-dependent model of each galaxy. We measure the magnitudes, effective radius (Re), the Sérsic index (n), axis ratio, and position angle in each band. The sample contains 790 cluster members (located close to the cluster centre < 0.64 R200) and 254 non-member galaxies that we further separate based on their morphology into ellipticals, lenticulars, and spirals. We find that the Sérsic index of all galaxies inside clusters remains nearly constant with wavelength while Re decreases as wavelength increases for all morphological types. We do not observe a significant variation on n and Re as a function of projected local density and distance from the clusters centre. Comparing the n and Re of bright cluster galaxies with a subsample of non-member galaxies we find that bright cluster galaxies are more concentrated (display high n values) and are more compact (low Re). Moreover, the light profile and size of bright cluster galaxies does not change as a function of wavelength in the same manner as non-member galaxies
GASP II. A MUSE view of extreme ram-pressure stripping along the line of sight: kinematics of the jellyfish galaxy JO201
This paper presents a spatially-resolved kinematic study of the jellyfish
galaxy JO201, one of the most spectacular cases of ram-pressure stripping (RPS)
in the GASP (GAs Stripping Phenomena in Galaxies with MUSE) survey. By studying
the environment of JO201, we find that it is moving through the dense
intra-cluster medium of Abell 85 at supersonic speeds along our line of sight,
and that it is likely accompanied by a small group of galaxies. Given the
density of the intra-cluster medium and the galaxy's mass, projected position
and velocity within the cluster, we estimate that JO201 must so far have lost
~50% of its gas during infall via RPS. The MUSE data indeed reveal a smooth
stellar disk, accompanied by large projected tails of ionised (Halpha) gas,
composed of kinematically cold (velocity dispersion <40km/s) star-forming knots
and very warm (>100km/s) diffuse emission which extend out to at least ~50 kpc
from the galaxy centre. The ionised Halpha-emitting gas in the disk rotates
with the stars out to ~6 kpc but in the disk outskirts becomes increasingly
redshifted with respect to the (undisturbed) stellar disk. The observed
disturbances are consistent with the presence of gas trailing behind the
stellar component, resulting from intense face-on RPS happening along the line
of sight. Our kinematic analysis is consistent with the estimated fraction of
lost gas, and reveals that stripping of the disk happens outside-in, causing
shock heating and gas compression in the stripped tails.Comment: ApJ, revised version after referee comments, 15 pages, 16 figures.
The interactive version of Figure 9 can be viewed at
web.oapd.inaf.it/gasp/publications.htm
OmegaWINGS: OmegaCAM@VST observations of WINGS galaxy clusters
The Wide-field Nearby Galaxy-cluster Survey (WINGS) is a wide-field
multi-wavelength survey of X-ray selected clusters at z =0.04-0.07. The
original 34'x34' WINGS field-of- view has now been extended to cover a 1 sq.deg
field with both photometry and spectroscopy. In this paper we present the
Johnson B and V-band OmegaCAM/VST observations of 46 WINGS clusters, together
with the data reduction, data quality and Sextractor photometric catalogs.
With a median seeing of 1arcs in both bands, our 25-minutes exposures in each
band typically reach the 50% completeness level at V=23.1 mag. The quality of
the astrometric and photometric accuracy has been verified by comparison with
the 2MASS as well as with SDSS astrometry, and SDSS and previous WINGS imaging.
Star/galaxy separation and sky-subtraction procedure have been tested comparing
with previous WINGS data.
The Sextractor photometric catalogues are publicly available at the CDS, and
will be included in the next release of the WINGS database on the VO together
with the OmegaCAM reduced images. These data form the basis for a large ongoing
spectroscopic campaign with AAOmega/AAT and is being employed for a variety of
studies. [abridged]Comment: submitted to A&
The hybrid solution for the Fundamental Plane
By exploiting the database of early-type galaxies (ETGs) members of the WINGS
survey of nearby clusters, we address here the long debated question of the
origin and shape of the Fundamental Plane (FP). Our data suggest that different
physical mechanisms concur in shaping and tilting the FP with respect to the
virial plane (VP) expectation. In particular, an hybrid solution in which the
structure of galaxies and their stellar population are the main contributors to
the FP tilt seems to be favoured. We find that the bulk of the tilt should be
attributed to structural non-homology, while stellar population effects play an
important but less crucial role. Our data indicate that the differential FP
tilt between the V and K-band is due to a sort of entanglement between
structural and stellar population effects, for which the inward steepening of
color profiles (V-K) tends to increase at increasing the stellar mass of ETGs.
The same analysis applied to the ATLAS3D and SDSS data in common with WINGS
(WSDSS throughout the paper) confirms our results, the only remarkable
difference being the less important role of the stellar mass-to-light-ratio in
determining the FP tilt. The ATLAS3D data also suggest that the tilt depends as
well on the dark matter (DM) fraction and on the rotational contribution to the
kinetic energy (Vrot/sigma). We show that the global properties of the FP can
be understood in terms of the underlying correlation among mass, structure and
stellar population of ETGs, for which, at increasing the stellar mass, ETGs
become (on average) older and more centrally concentrated. Finally, we show
that a Malmquist-like selection effect may mimic a differential evolution of
the mass-to-light ratio for galaxies of different masses. This should be taken
into account in the studies investigating the amount of the so called
downsizing phenomenon.Comment: 22 pages, 17 figure
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