230 research outputs found
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
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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
Star formation history of galaxies from z=0 to z=0.7 A backward approach to the evolution of star-forming galaxies
We investigate whether the mean star formation activity of star-forming
galaxies from z=0 to z=0.7 in the GOODS-S field can be reproduced by simple
evolution models of these systems. In this case, such models might be used as
first order references for studies at higher z to decipher when and to what
extent a secular evolution is sufficient to explain the star formation history
in galaxies.
We selected star-forming galaxies at z=0 and at z=0.7 in IR and in UV to have
access to all the recent star formation. We focused on galaxies with a stellar
mass ranging between 10^{10} and 10^{11} M_sun for which the results are not
biased by the selections. We compared the data to chemical evolution models
developed for spiral galaxies and originally built to reproduce the main
characteristics of the Milky Way and nearby spirals without fine-tuning them
for the present analysis. We find a shallow decrease in the specific star
formation rate (SSFR) when the stellar mass increases. The evolution of the
SSFR characterizing both UV and IR selected galaxies from z=0 to z=0.7 is
consistent with the models built to reproduce the present spiral galaxies.
There is no need to strongly modify of the physical conditions in galaxies to
explain the average evolution of their star formation from z=0 to z=0.7. We use
the models to predict the evolution of the star formation rate and the
metallicity on a wider range of redshift and we compare these predictions with
the results of semi-analytical models.Comment: 14 pages, 10 figures. accepted for publication in Astronomy &
Astrophysic
Spiral-like star-forming patterns in CALIFA early-type galaxies
Based on a combined analysis of SDSS imaging and CALIFA integral field
spectroscopy data, we report on the detection of faint (24 < {\mu}
mag/arcsec < 26) star-forming spiral-arm-like features in the periphery of
three nearby early-type galaxies (ETGs). These features are of considerable
interest because they document the still ongoing inside-out growth of some
local ETGs and may add valuable observational insight into the origin and
evolution of spiral structure in triaxial stellar systems. A characteristic
property of the nebular component in the studied ETGs, classified i+, is a
two-radial-zone structure, with the inner zone that displays faint
(EW(H\alpha)1{\AA}) low-ionization nuclear emission-line region (LINER)
properties, and the outer one (3{\AA}<EW(H\alpha)<~20{\AA}) HII-region
characteristics. This spatial segregation of nebular emission in two physically
distinct concentric zones calls for an examination of aperture effects in
studies of type i+ ETGs with single-fiber spectroscopic data.Comment: Accepted to A&A, 5 pages, 1 figur
First survey of Wolf-Rayet star populations over the full extension of nearby galaxies observed with CALIFA
The search of extragalactic regions with conspicuous presence of Wolf-Rayet
(WR) stars outside the Local Group is challenging task due to the difficulties
in detecting their faint spectral features. In this exploratory work, we
develop a methodology to perform an automated search of WR signatures through a
pixel-by-pixel analysis of integral field spectroscopy (IFS) data belonging to
the Calar Alto Legacy Integral Field Area survey, CALIFA. This technique
allowed us to build the first catalogue of Wolf-Rayet rich regions with
spatially-resolved information, allowing to study the properties of these
complexes in a 2D context. The detection technique is based on the
identification of the blue WR bump (around He II 4686 {\AA}, mainly associated
to nitrogen-rich WR stars, WN) and the red WR bump (around C IV 5808 {\AA} and
associated to carbon-rich WR stars, WC) using a pixel-by-pixel analysis. We
identified 44 WR-rich regions with blue bumps distributed in 25 galaxies of a
total of 558. The red WR bump was identified only in 5 of those regions. We
found that the majority of the galaxies hosting WR populations in our sample
are involved in some kind of interaction process. Half of the host galaxies
share some properties with gamma-ray burst (GRB) hosts where WR stars, as
potential candidates to being the progenitors of GRBs, are found. We also
compared the WR properties derived from the CALIFA data with stellar population
synthesis models, and confirm that simple star models are generally not able to
reproduce the observations. We conclude that other effects, such as the binary
star channel (which could extend the WR phase up to 10 Myr), fast rotation or
other physical processes that causes the loss of observed Lyman continuum
photons, are very likely affecting the derived WR properties, and hence should
be considered when modelling the evolution of massive stars.Comment: 33 pages, accepted for publication in A&
Spectroscopic aperture biases in inside-out evolving early-type galaxies from CALIFA
Integral field spectroscopy studies based on CALIFA data have recently
revealed the presence of ongoing low-level star formation (SF) in the periphery
of ~10% of local early-type galaxies (ETGs), witnessing a still ongoing
inside-out galaxy growth process. A distinctive property of the nebular
component in these ETGs, classified i+, is a two-radial-zone structure, with
the inner zone displaying LINER emission with a H\alpha equivalent width
EW~1{\AA}, and the outer one (3{\AA}<EW<~20{\AA}) showing HII-region
characteristics. Using CALIFA IFS data, we empirically demonstrate that the
confinement of nebular emission to the galaxy periphery leads to a strong
aperture (or, redshift) bias in spectroscopic single-fiber studies of type i+
ETGs: At low redshift (<~0.45), SDSS spectroscopy is restricted to the inner
(SF-devoid LINER) zone, thereby leading to their erroneous classification as
"retired" galaxies (systems lacking SF and whose faint emission is powered by
pAGB stars). Only at higher z's the SDSS aperture can encompass the outer SF
zone, permitting their unbiased classification as "composite SF/LINER". We also
demonstrate that the principal effect of a decreasing aperture on the
classification of i+ ETGs via standard BPT emission-line ratios consists in a
monotonic up-right shift precisely along the upper-right wing of the "seagull"
distribution. Motivated by these insights, we also investigate theoretically
these biases in aperture-limited studies of inside-out growing galaxies as a
function of z. To this end, we devise a simple model, which involves an
outwardly propagating SF process, that reproduces the radial extent and
two-zone EW distribution of i+ ETGs. By simulating on this model the
spectroscopic SDSS aperture, we find that SDSS studies at z<~1 are
progressively restricted to the inner LINER-zone, and miss an increasingly
large portion of the H\alpha-emitting periphery.Comment: Accepted to A&A, 6 pages, 4 figure
Trombosis valvular y terapia trombolítica en la era moderna: reporte de un caso
Prosthetic valve thrombosis is a feared complication with an annual incidence ranging between 0.3 to 1.3%. Diagnostic approach is essential for a better prognosis and ultimately determines the chosen therapeutic strategy. Emergent valvular surgery is usually recommended in hemodinamically unstable patients, large thrombus or recurrent embolic episodes. These high-risk conditions are often not the case. Therefore, in many patients the surgical risk is much greater than that of bleeding associated with thrombolytic administration. Ultra-slow infusions have been reported with similar efficacy and lower rates of bleeding complications. We present a case of mitral prosthetic valve thrombosis considered not feasible to surgical management and subsequently treated with an ultra-slow tissue plasminogen activator infusion.La trombosis obstructiva de válvulas mecánicas es una complicación temida con una incidencia aproximada de 0,3 – 1,3% por año. El diagnóstico oportuno es fundamental en el pronóstico y determinará la opción terapéutica más adecuada. La cirugía valvular urgente se recomienda en pacientes con inestabilidad hemodinámica, trombos de gran tamaño o embolismos recurrentes. Cuando no se cumplen estas condiciones, es frecuente que la opción quirúrgica involucre un riesgo prohibitivo y superior al riesgo de sangrado asociado con la terapia trombolítica. En este contexto, la infusión ultralenta de activador tisular del plasminógeno se ha reportado con una eficacia similiar y menores tasas de complicaciones hemorrágicas con relación a otros esquemas. A continuación se discute un caso de trombosis valvular mitral con contraindicación quirúrgica, que fue tratado de forma exitosa con un esquema de trombolisis ultralenta
A new scaling relation for HII regions in spiral galaxies: unveiling the true nature of the mass-metallicity relation
We demonstrate the existence of a -local- relation between galaxy surface
mass density, gas metallicity, and star-formation rate density using
spatially-resolved optical spectroscopy of HII regions in the local Universe.
One of the projections of this distribution, -the local mass-metallicity
relation- extends over three orders of magnitude in galaxy mass density and a
factor of eight in gas metallicity. We explain the new relation as the combined
effect of the differential radial distributions of mass and metallicity in the
discs of galaxies, and a selective star-formation efficiency. We use this local
relation to reproduce -with remarkable agreement- the total mass-metallicity
relation seen in galaxies, and conclude that the latter is a scale-up
integrated effect of a local relation, supporting the inside-out growth and
downsizing scenarios of galaxy evolution.Comment: Accepted for publication in Astrophysical Journal Letters, 5 pages, 4
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