97 research outputs found
Metallicity of high stellar mass galaxies with signs of merger events
We focus on an analysis of galaxies of high stellar mass and low metallicity.
We cross-correlated the Millenium Galaxy Catalogue (MGC) and the Sloan Digital
Sky Survey (SDSS) galaxy catalogue to provide a sample of MGC objects with high
resolution imaging and both spectroscopic and photometric information available
in the SDSS database. For each galaxy in our sample, we conducted a systematic
morphological analysis by visual inspection of MGC images using their
luminosity contours. The galaxies are classified as either disturbed or
undisturbed objects. We divide the sample into three metallicity regions,
within wich we compare the properties of disturbed and undisturbed objects. We
find that the fraction of galaxies that are strongly disturbed, indicative of
being merger remnants, is higher when lower metallicity objects are considered.
The three bins analysed consist of approximatively 15%, 20%, and 50% disturbed
galaxies (for high, medium, and low metallicity, respectively). Moreover, the
ratio of the disturbed to undisturbed relative distributions of the population
age indicator, Dn(4000), in the low metallicity bin, indicates that the
disturbed objects have substantially younger stellar populations than their
undisturbed counterparts. In addition, we find that an analysis of colour
distributions provides similar results, showing that low metallicity galaxies
with a disturbed morphology are bluer than those that are undisturbed. The
bluer colours and younger populations of the low metallicity, morphologically
disturbed objects suggest that they have experienced a recent merger with an
associated enhanced star formation rate. [abridged]Comment: Astronomy & Astrophysics, in pres
Building Blocks in Hierarchical Clustering Scenarios and their Connection with Damped Ly Systems
We carried out a comprehensive analysis of the chemical properties of the
interstellar medium (ISM) and the stellar population (SP) of current normal
galaxies and their progenitors in a hierarchical clustering scenario. We
compared the results with observations of Damped Lyman- systems (DLAs)
under the hypothesis that, at least, part of the observed DLAs could originate
in the building blocks of today normal galaxies. We used a hydrodynamical
cosmological code which includes star formation and chemical enrichment.
Galaxy-like objects are identified at and then followed back in time.
Random line-of-sights (LOS) are drawn through these structures in order to
mimic Damped Lyman systems. We then analysed the chemical properties
of the ISM and SP along the LOS. We found that the progenitors of current
galaxies in the field with mean and virial circular velocity of
could be the associated DLA galaxies. For these systems
we detected a trend for to increase with redshift.(Abridged)Comment: 15 pages, 11 Postscript figures. Accepted to MNRA
Satellite Galaxies and Fossil Groups in the Millennium Simulation
We use a semianalytic galaxy catalogue constructed from the Millennium
Simulation to study the satellites of isolated galaxies in the LCDM cosmogony.
This sample (~80,000$ bright primaries, surrounded by ~178,000 satellites)
allows the characterization, with minimal statistical uncertainty, of the
dynamical properties of satellite/primary galaxy systems in a LCDM universe. We
find that, overall, the satellite population traces the dark matter rather
well: its spatial distribution and kinematics may be approximated by an NFW
profile with a mildly anisotropic velocity distribution. Their spatial
distribution is also mildly anisotropic, with a well-defined ``anti-Holmberg''
effect that reflects the misalignment between the major axis and angular
momentum of the host halo. The isolation criteria for our primaries picks not
only galaxies in sparse environments, but also a number of primaries at the
centre of ''fossil'' groups. We find that the abundance and luminosity function
of these unusual systems are in reasonable agreement with the few available
observational constraints. We recover the expected L_{host} \sigma_{sat}^3
relation for LCDM models for truly-isolated primaries. Less strict primary
selection, however, leads to substantial modification of the scaling relation.
Our analysis also highlights a number of difficulties afflicting studies that
rely on blind stacking of satellite systems to constrain the mean halo mass of
the primary galaxies.Comment: 18 pages, 14 figures, MNRAS in press. Accepted version with minor
changes. Version with high resolution figures available at:
http://www.astro.uvic.ca/~lsales/SatPapers/SatPapers.htm
Dependence of Galaxy Shape on Environment in the Sloan Digital Sky Survey
Using a sample of galaxies from the Sloan Digital Sky Survey (SDSS) Data
Release 4, we study the trends relating surface brightness profile type and
apparent axis ratio to the local galaxy environment. We use the SDSS parameter
`fracDeV' to quantify the profile type. We find that galaxies with M_r > -18
are mostly described by exponential profiles in all environments. Galaxies with
-21 < M_r < -18 mainly have exponential profiles in low density environments
and de Vaucouleurs profiles in high density environments. The most luminous
galaxies, with M_r < -21, are mostly described by de Vaucouleurs profiles in
all environments. For galaxies with M_r < -19, the fraction of de Vaucouleurs
galaxies is a monotonically increasing function of local density, while the
fraction of exponential galaxies is monotonically decreasing. For a fixed
surface brightness profile type, apparent axis ratio is frequently correlated
with environment. As the local density of galaxies increases, we find that for
-20 < M_r < -18, galaxies of all profile types become slightly rounder, on
average; for -22 < M_r < -20, galaxies with exponential profiles tend to become
flatter, while galaxies with de Vaucouleurs profiles become rounder; for M_r <
-22, galaxies with exponential profiles become flatter, while the de
Vaucouleurs galaxies become rounder in their inner regions, yet exhibit no
change in their outer regions. We comment on how the observed trends relate to
the merger history of galaxies.Comment: 23 pages, 7 figures, accepted by Ap
The host galaxies of long-duration GRBs in a cosmological hierarchical scenario
We developed a Monte Carlo code to generate long-duration gamma ray burst
(LGRB) events within cosmological hydrodynamical simulations consistent with
the concordance model. As structure is assembled, LGRBs are generated in the
substructure that formed galaxies today. We adopted the collapsar model so that
LGRBs are produced by single, massive stars at the final stage of their
evolution. We found that the observed properties of the LGRB host galaxies
(HGs) are reproduced if LGRBs are also required to be generated by low
metallicity stars. The low metallicity condition imposed on the progenitor
stars of LGRBs selects a sample of HGs with mean gas abundances of 12 + log O/H
\~ 8.6. For z<1 the simulated HGs of low metallicity LGRB progenitors tend to
be faint, slow rotators with high star formation efficiency, compared with the
general galaxy population, in agreement with observations. At higher redshift,
our results suggest that larger systems with high star formation activity could
also contribute to the generation of LGRBs from low metallicity progenitors
since the fraction of low metallicity gas available for star formation
increases for all systems with look-back time. Under the hypothesis of our LGRB
model, our results support the claim that LGRBs could be unbiased tracers of
star formation at high redshifts.Comment: Final revised version with minor changes. 9 pages, 9 figures,
mn2e.cls. To appear in MNRA
Nitrogen Abundances in DLA Systems: The Combined Effects of SNII and SNIa in a Hierarchical Clustering Scenario
The combined enrichment of Supernovae II and I in a hierarchical clustering
scenario could produce regions with low N content respect to -elements
consistent with observed values measured in Damped Ly- (DLAs). We have
studied the formation of DLAs in a hierarchical clustering scenario under the
hypothesis that the building blocks of current field galaxies could be part of
the structures mapped by DLAs. In our models the effects of the non-linear
evolution of the structure (which produces bursty star formation histories, gas
infall, etc.) and the contributions of SNIa and SNII are found to be
responsible of producing these N regions with respect to the -elements.
Although SNIa are not main production sites for Si or O, because of the
particular timing Consistently, we found the simulated low nitrogen DLAs to
have sub-solar [Fe/H]. We show that low nitrogen DLAs have experienced
important star formation activity in the past with higher efficiency than
normal DLAs. Our chemical model suggests that SNIa play a relevant role in the
determination of the abundance pattern of DLA and, that the observed low
nitrogen DLA frequency could be explained taking into account the time-delay of
0.5 Gyr introduced by these supernova to release metals.Comment: 4 pages, 2 Postscript figures. Accepted for publication in MNRAS
(pink pages
Effects of mergers and galaxy interactions at intermediate densities in the SDSS-DR4
Recently, several observational works have provided evidence in favor of a pre-processing of galaxies at moderate environments. These evidences show that the transition of galaxies onto the red-sequence could take place in galaxy groups in the outskirt of clusters or in the infalling populations. Based on the evidence that interacting and merging systems are priviledged found at intermediate densities, we use the SDSSDR4 data to analyse the role of mergers and close galaxy interactions as environmental processes to lead to evolutionary transformations. We explore the properties of galaxy pairs and merging systems at different local and global density environments, comparing them with those of isolated galaxies in an unbiased control sample.Recientemente varios autores han aportado evidencia observacional que sugerir´ıa que las galaxias son pre-procesadas en regiones de densidad intermedia, produciendo una gran transformacion en las mismas. Estos resultados observacionales muestran que la transicion de las galaxias hacia la secuencia roja se producir´ıa en regiones perifericas de los cumulos de galaxias. Por otra parte, existe evidencia tanto teorica como observacional que indicar´ıa que las interacciones y fusiones de galaxias son particularmente frecuentes en estas regiones. En este trabajo analizamos el rol de las interacciones y colisiones de galaxias en regiones de densidad intermedia, utilizando para tal efecto galaxias del cat´alogo SDSS-DR4.Facultad de Ciencias Astronómicas y GeofísicasConsejo Nacional de Investigaciones Científicas y Técnica
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