653 research outputs found
Catching Spiral - S0 transition in groups. Insights from SPH simulations with chemo-photometric implementation
We are investigating the co-evolution of galaxies within groups combining
multi-wavelength photometric and 2D kinematical observations. Here we focus on
S0s showing star formation in ring/arm-like structures. We use smooth particle
hydrodynamical simulations (SPH) with chemo-photometric implementation which
provide dynamical and morphological information together with the spectral
energy distribution (SED) at each evolutionary stage. As test cases, we
simulate the evolution of two such S0s: NGC 1533 and NGC 3626. The merging of
two halos with mass ratio 2:1, initially just composed of dark matter (DM) and
gas, well match their observed SEDs, their surface brightness profiles and
their overall kinematics. The residual star formation today "rejuvenating" the
ring/arm like structures in these S0s is then a mere consequence of a major
merger, i.e. this is a phase during the merger episode. The peculiar
kinematical features, e.g. gas-stars counter rotation in NGC 3626, depends on
the halos initial impact parameters. Furthermore, our simulations allow to
follow, in a fully consistent way, the transition of these S0s through the
green valley in the NUV-r vs. Mr colour magnitude diagram, which they cross in
about 3-5 Gyr, before reaching their current position in the red sequence. We
conclude that a viable mechanism driving the evolution of S0s in groups is of
gravitational origin.Comment: 30 pages, 6 figures; accepted for publication in Advances in Space
Research, Special Issue: Ultraviolet Astrophysic
Galaxy evolution in groups. USGC U268 and USGC U376 in the Leo cloud
With the aim of investigating galaxy evolution in nearby galaxy groups, we
analysed the spectral energy distribution of 24 galaxies, members of two groups
in the Leo cloud, USGC U268 and USGC U376. We estimated the ages and stellar
masses of the galaxies by fitting their total apparent magnitudes from
far-ultraviolet to near-infrared with population synthesis models. The
comparison of the results for a subsample of galaxies with smooth particle
hydrodynamic (SPH) simulations with chemo-photometric implementation, shows
that in most cases the estimated stellar masses obtained with the two different
approaches are in good agreement. The kinematical and dynamical analysis
indicates that USGC U268 is in a pre-virial collapse phase while USGC U376 is
likely in a more evolved phase towards virialization.Comment: 16 pages, 6 figures; accepted for publication in Advances in Space
Research, Special Issue: Ultraviolet Astrophysic
Optical properties of the NGC 5328 group of galaxies
We present the results of a photometric and spectroscopic study of seven
members of the NGC 5328 group of galaxies, a chain of galaxies spanning over
200 kpc (H_0 = 70 km/s/Mpc). We analyze the galaxy structure and study the
emission line properties of the group members looking for signatures of star
formation and AGN activity. We finally attempt to infer, from the modeling of
line-strength indices, the stellar population ages of the early-type members.
We investigate also the presence of a dwarf galaxy population associated with
the bright members.
The group is composed of a large fraction of early-type galaxies including
NGC 5328 and NGC 5330, two bona fide ellipticals at the center of the group. In
both galaxies no recent star formation episodes are detected by the H_beta vs.
MgFe indices of these galaxies. 2MASX J13524838-2829584 has extremely boxy
isophotes which are believed to be connected to a merging event: line strength
indices suggest that this object probably had a recent star formation episode.
A warped disc component emerges from the model subtracted image of 2MASX
J13530016-2827061 which is interpreted as a signature of an ongoing interaction
with the rest of the group.
Ongoing star formation and nuclear activity is present in the projected
outskirts of the group. The two early-type galaxies 2MASX J13523852-2830444 and
2MASX J13525393-2831421 show spectral signatures of star formation, while a
Seyfert 2 type nuclear activity is detected in MCG -5-33-29.Comment: 18 pages, 12 figures, accepted for publication in MNRA
A multi-wavelength study of the evolution of Early-Type Galaxies in Groups: the ultraviolet view
ABRIDGED- The UV-optical color magnitude diagram (CMD) of rich galaxy groups
is characterised by a well developed Red Sequence (RS), a Blue Cloud (BC) and
the so-called Green Valley (GV). Loose, less evolved groups of galaxies likely
not virialized yet may lack a well defined RS. This is actually explained in
the framework of galaxy evolution. We are focussing on understanding galaxy
migration towards the RS, checking for signatures of such a transition in their
photometric and morphological properties. We report on the UV properties of a
sample of ETGs galaxies inhabiting the RS. The analysis of their structures, as
derived by fitting a Sersic law to their UV luminosity profiles, suggests the
presence of an underlying disk. This is the hallmark of dissipation processes
that still must have a role in the evolution of this class of galaxies. SPH
simulations with chemo-photometric implementations able to match the global
properties of our targets are used to derive their evolutionary paths through
UV-optical CDM, providing some fundamental information such as the crossing
time through the GV, which depends on their luminosity. The transition from the
BC to the RS takes several Gyrs, being about 3-5 Gyr for the the brightest
galaxies and more long for fainter ones, if it occurs. The photometric study of
nearby galaxy structures in UV is seriously hampered by either the limited FoV
of the cameras (e.g in HST) or by the low spatial resolution of the images (e.g
in the GALEX). Current missions equipped with telescopes and cameras sensitive
to UV wavelengths, such as Swift-UVOT and Astrosat-UVIT, provide a relatively
large FoV and better resolution than the GALEX. More powerful UV instruments
(size, resolution and FoV) are obviously bound to yield fundamental advances in
the accuracy and depth of the surface photometry and in the characterisation of
the galaxy environment.Comment: 12 pages, 6 figures: accepted for publication in Astrophysics & Space
Science as contributions to the workshop: "UV astronomy, the needs and the
means
Galaxy evolution in nearby groups. II. Galaxy evolution in nearby loose groups. II. Photometric and kinematic characterization of USGC U268 and USGC U376 group members in the Leo cloud
We present the photometric and kinematic characterization of two groups, USGC
U268 and USGC U376 located in different regions of the Leo cloud. U268,
composed of 10 catalogued members and 11 new added members, has a small
fraction (~24%) of early-type galaxies (ETGs). U376 has 16 plus 8 new added
members, with ~38% of ETGs. We find the presence of significant substructures
in both groups suggesting that they are likely accreting galaxies. U268 is
located in a more loose environment than U376. For each member galaxy, broad
band integrated and surface photometry have been obtained in far-UV and near-UV
with GALEX, and in u,g, r, i, z (SDSS) bands. H_alpha imaging and 2D high
resolution kinematical data have been obtained using PUMA Scanning Fabry-Perot
interferometer at the 2.12 m telescope in San Pedro M\'artir, (Baja California,
M\'exico). We improved the galaxy classification and we detected morphological
and kinematical distortions that may be connected to either on-going and/or
past interaction/accretion events or environmental induced secular evolution.
U268 appears more active than U376, with a large fraction of galaxies showing
interaction signatures (60% vs. 13%). The presence of bars among late-type
galaxies is ~10% in U268 and ~$29% in U376. The cumulative distribution of (FUV
- NUV) colours of galaxies in U268 is significantly different than that in U376
with galaxies in U268 bluer than those in U376. In the (FUV-r vs. M_r) and
(NUV-r vs. M_r) planes no members of U268 are found in the `red sequence', even
early-type galaxies lie in the `blue sequence' or in the `green valley'. Most
(80%) of the early-type members in U376 inhabits the `red sequence, a large
fraction of galaxies, of different morphological types, are located in the
`green valley', while the `blue sequence' is under-populated with respect to
U268.Comment: 27 pages, 11 figures, 8 tables, accepted for publication in MNRAS
(abridged abstract
Early Type Galaxies in the Mid Infrared: a new flavor to their stellar populations
The mid infrared emission of early type galaxies traces the presence of
intermediate age stellar populations as well as even tiny amounts of ongoing
star formation. Here we discuss high S/N Spitzer IRS spectra of a sample of
Virgo early type galaxies, with particular reference to NGC 4435. We show that,
by combining mid infrared spectroscopic observations with existing broad band
fluxes, it is possible to obtain a very clean picture of the nuclear activity
in this galaxy.Comment: 4 pages; proceedings of IAU Symposium No. 241, "Stellar Populations
as Building Blocks of Galaxies", editors A. Vazdekis and R. Peletie
The Millennium Galaxy Catalogue: Dynamically Close Galaxy Pairs and the Global Merger Rate
We derive the number of dynamically close companions per galaxy () and
their total luminosity () for galaxies in the Millennium Galaxy Catalogue:
is similar to the fraction of galaxies in close pairs and is directly
related to the galaxy merger rate. We find and
for galaxies with and , for galaxies with , with
. The integrated merger rate to for both samples is about 20
%, but this depends sensitively on the fraction of kinematic pairs that are
truly undergoing a merger (assumed here to be 50%), the evolution of the merger
rate (here as ) and the adopted timescale for mergers (0.2 and 0.5 Gyr
for each sample, respectively). Galaxies involved in mergers tend to be
marginally bluer than non-interacting galaxies and show an excess of both
early-type and very late-type objects and a deficiency of intermediate-type
spirals. This suggests that interactions and mergers partly drive the star
formation and morphological evolution of galaxies.Comment: 26 pages, 3 figures, AJ accepted for publicatio
VEGAS: a VST Early-type GAlaxy Survey. IV. NGC 1533, IC 2038 and IC 2039: an interacting triplet in the Dorado group
This paper focuses on NGC 1533 and the pair IC 2038 and IC 2039 in Dorado a
nearby, clumpy, still un-virialized group. We obtained their surface photometry
from deep OmegaCAM@ESO-VST images in g and r bands. For NGC 1533, we map the
surface brightness down to mag/arcsec and mag/arcsec and out to about . At such faint levels
the structure of NGC 1533 appear amazingly disturbed with clear structural
asymmetry between inner and outer isophotes in the North-East direction. We
detect new spiral arm-like tails in the outskirts, which might likely be the
signature of a past interaction/merging event. Similarly, IC 2038 and IC 2039
show tails and distortions indicative of their ongoing interaction. Taking
advantages of deep images, we are able to detect the optical counterpart to the
HI gas. The analysis of the new deep data suggests that NGC 1533 had a complex
history made of several interactions with low-mass satellites that generated
the star-forming spiral-like structure in the inner regions and are shaping the
stellar envelope. In addition, the VST observations show that also the two less
luminous galaxies, IC 2038 and IC 2039, are probably interacting each-other
and, in the past, IC 2038 could have also interacted with NGC 1533, which
stripped away gas and stars from its outskirts. The new picture emerging from
this study is of an interacting triplet, where the brightest galaxy NGC 1533
has ongoing mass assembly in the outskirts.Comment: Accepted for publication in The Astronomical Journal. High-resolution
version of paper is available at the following link:
https://www.dropbox.com/preview/VEGAS_IV.pdf?role=persona
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