256 research outputs found
MEGADES: MEGARA galaxy disc evolution survey
The main interest of the science team for the exploitation of the MEGARA instrument at the 10.4m Gran Telescopio Canarias (GTC)
is devoted to the study of nearby galaxies. The focus lies on researching the history of star formation, and the chemical and kinematical
properties of disc systems. We refer to this project as MEGADES: the MEGARA galaxy disc evolution survey. The initial goal of
MEGADES is to provide a detailed study of the inner regions of nearby disc galaxies in terms of their spectrophotometric and chemical
evolution, and to provide a dynamical characterisation by distinguishing the contribution of in situ and ex situ processes to the history of
star formation and effective chemical enrichment of these regions. In addition, the dynamical analysis of these inner regions naturally
includes the identification and characterisation of galactic winds that might be present in these regions. At a later stage, we will extend
this study farther out in galactocentric distance. The first stage of this project encompasses the analysis of the central regions of 43
nearby galaxies observed with the MEGARA integral field unit for ∼114 h, including both guaranteed time and open time observations.
In this paper we provide a set of all the processed data products available to the community and early results from the analysis of these
data regarding stellar continuum and ionised and neutral gas features.GRANTECANEuropean Regional Development Funds (ERDF), through Programa Operativo Canarias FEDER 2014-2020Ministry of Science and Innovation, Spain (MICINN)
Spanish GovernmentNational Aeronautics & Space Administration (NASA)National Science Foundation (NSF)University of MarylandEotvos Lorand University (ELTE) RTI2018-096188-B-I00
AYA2016-75808-R
MCIN/AEI/10.13039/501100011033United States Department of Energy (DOE)
Los Alamos National Laboratory NNX08AR22GGordon and Betty Moore Foundation AST-123887
An investigation of star formation and dust attenuation in major mergers using ultraviolet and infrared data
Merger processes play an important role in galaxy formation and evolution. To
study the influence of merger processes on the evolution of dust properties and
cosmic star formation rate, we investigate a local sample of major merger
galaxies and a control sample of isolated galaxies using GALEX ultraviolet (UV)
and Spitzer infrared (IR) images. Through a statistical study, we find that
dust attenuation in merger galaxies is enhanced with respect to isolated
galaxies. We find this enhancement is contributed mainly by spiral galaxies in
spiral-spiral (S-S) pairs, and increases with the increasing stellar mass of a
galaxy. Combining the IR and UV parts of star formation rates (SFRs), we then
calculated the total SFRs and specific star formation rates (SSFRs). We find
the SSFRs to be enhanced in merger galaxies. This enhancement depends on galaxy
stellar mass and the companion's morphology, but depends little on whether the
galaxy is a primary or secondary component or on the separation between two
components. These results are consistent with a previous study based only on IR
images. In addition, we investigate the nuclear contributions to SFRs. SFRs in
paired galaxies are more concentrated in the central part of the galaxies than
in isolate galaxies. Our studies of dust attenuation show that the nuclear
parts of pairs most resemble ULIRGs. Including UV data in the present work not
only provides reliable information on dust attenuation, but also refines
analyses of SFRs.Comment: 21 pages, 21 figure
Disentangling the role of environmental processes in galaxy clusters
In this work we present the results of a novel approach devoted to
disentangle the role of the environmental processes affecting galaxies in
clusters. This is based on the analysis of the NUV-r' distributions of a large
sample of star-forming galaxies in clusters spanning more than four absolute
magnitudes. The galaxies inhabit three distinct environmental regions: virial
regions, cluster infall regions and field environment. We have applied rigorous
statistical tests in order to analyze both, the complete NUV-r' distributions
and their averages for three different bins of r'-band galaxy luminosity down
to M_r' ~ -18, throughout the three environmental regions considered. We have
identified the environmental processes that significantly affect the
star-forming galaxies in a given luminosity bin by using criteria based on the
characteristics of these processes: their typical time-scales, the regions
where they operate and the galaxy luminosity range for which their effects are
more intense. We have found that the high-luminosity (M_r'<=-20) star-forming
galaxies do not show significant signs in their star formation activity neither
of being affected by the environment in the last ~10^8 yr nor of a sudden
quenching in the last 1.5 Gyr. The intermediate-luminosity (-20<M_r'<=-19)
star-forming galaxies appear to be affected by starvation in the virial regions
and by the harassment both, in the virial and infall regions. Low-luminosity
(-19<M_r'<=-18.2) star-forming galaxies seem to be affected by the same
environmental processes as intermediate-luminosity star-forming galaxies in a
stronger way, as it would be expected for their lower luminosities.Comment: 42 pages, 7 figures, 5 tables; accepted for publication in Ap
Recent star formation in clusters of galaxies: extreme compact starbursts in A539 and A634
We report on the detection of two Halpha-emitting extreme compact objects
from deep images of the Abell 634 and Abell 539 clusters of galaxies at z ~
0.03. Follow up long slit spectroscopy of these two unresolved sources revealed
that they are members of their respective clusters showing HII type spectra.
The luminosity and the extreme equivalent width of Halpha+[NII] measured for
these sources, together with their very compact appearance, has raised the
question about the origin of these intense starbursts in the cluster
environment. We propose the compact starburst in Abell 539 resulted from the
compression of the interstellar gas of a dwarf galaxy when entering the cluster
core; while the starburst galaxy in Abell 634 is likely to be the result of a
galaxy-galaxy interaction, illustrating the preprocessing of galaxies during
their infall towards the central regions of clusters. The contribution of these
compact star-forming dwarf galaxies to the star formation history of galaxy
clusters is discussed, as well as a possible link with the recently discovered
early-type ultra-compact dwarf galaxies. We note that these extreme objects
will be rarely detected in normal magnitude-limited optical or NIR surveys,
mainly due to their low stellar masses (of the order of 10^6 solar masses),
whereas they will easily show up in dedicated Halpha surveys given the high
equivalent width of their emission lines.Comment: Accepted for publication in the Astronomical Journal. 31 pages, 10
fig
The Luminosity Function of Galaxies in the Hercules Cluster
We have imaged 1 deg in the V-band in the direction of the
Hercules Cluster (Abell 2151). The data are used to compute for the first time
the luminosity function (LF) of galaxies in the cluster down to the dwarf
regime (M -13.85). The global LF is well described by a
Schechter function (\cite{schechter76}) with best-fit parameters =
-1.30 0.06 and M = -21.25 0.25. The radial dependence of
the LF has also been studied, finding that it turns out to be almost constant
within the errors even further away than the virial radius. Given the presence
of significant substructure within the cluster, we have analized the LFs in
different regions. While two of the subclusters present LFs consistent with
each other and with the global one, the southernmost one exhibits a somewhat
steeper faint-end slope.Comment: 3 pages, to appear in Proc. of IAU Colloq. 195: "Outskirts of Galaxy
Clusters: Intense Life in the Suburbs
The r'-band luminosity function of Abell1367: a comparison with Coma
We made a large (approximately 1degr x 1degr) r'-band imaging survey of the
central regions of the two nearby clusters of galaxies, Abell1367 and Coma. The
data, presented as a catalog, are used to construct the r'-band luminosity
function (LF) of galaxies in these two clusters, by subtracting the Yasuda et
al. (2001) galaxy counts from our cluster counts. Our Coma luminosity function
is consistent with previous determinations, i.e. providing a faint end slope
alpha = -1.47_-0.09^+0.08, significantly steeper than the one we find for
Abell1367 (alpha = -1.07_-0.16^+0.20). The counts in Abell1367 show a relative
minimum at r' ~ 19, followed by a steep increase faintward. The difference
between the two clusters appears significant, given the consistency of the
experimental conditions in the two clusters. Whereas for Coma we find a
significant increase of the slope of the LF outwards, no such effect is found
for Abell1367.Comment: 12 pages, 8 figures, accepted for publication in A&
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