1,097 research outputs found
Metallicity in damped Lyman-alpha systems: evolution or bias?
Assuming that damped Lyman-alpha(DLA) systems are galactic discs, we
calculate the corresponding evolution of metal abundances. We use detailed
multi-zone models of galactic chemical evolution (reproducing successfully the
observed properties of disc galaxies) and appropriate statistics (including
geometrical propability factors) to calculate the average metallicity as a
function of redshift. The results are compatible with available observations,
provided that observational biases are taken into account, as suggested by
Boisse et al. (1998). In particular, high column density and high metallicity
systems are not detected because the light of backround quasars is severely
extinguished, while low column density and low metallicity systems are not
detectable through their absorption lines by current surveys. We show that
these observational constraints lead to a ``no-evolution'' picture for the DLA
metallicity, which does not allow to draw strong conclusions about the nature
of those systems or about their role in ``cosmic chemical evolution''.Comment: 7 pages, 5 figures, MNRAS in pres
Chemo-spectrophotometric evolution of spiral galaxies: III. Abundance and colour gradients in discs
We study the relations between luminosity and chemical abundance profiles of
spiral galaxies, using detailed models for the chemical and spectro-photometric
evolution of galactic discs. The models are ``calibrated'' on the Milky Way
disc and are successfully extended to other discs with the help of simple
``scaling'' relations, obtained in the framework of semi-analytic models of
galaxy formation. We find that our models exhibit oxygen abundance gradients
that increase in absolute value with decreasing disc luminosity (when expressed
in dex/kpc) and are independent of disc luminosity (when expressed in
dex/scalelength), both in agreement with observations. We notice an important
strong correlation between abundance gradient and disc scalelength. These
results support the idea of ``homologuous evolution'' of galactic discs.Comment: 9 pages, 6 postscript figures, MNRAS in pres
Chemical evolution and depletion pattern in Damped Lyman-alpha (DLA) systems
In this paper we point out a previously unnoticed anticorrelation between the
observed abundance ratio [X/Zn] (where Zn is assumed to be undepleted and X
stands for the refractories Fe, Cr and Ni) and metal column density
([Zn/H]+log(N{HI})) in DLAs. We suggest that this trend is an unambiguous sign
of dust depletion, since metal column density is a measure of the amount of
dust along the line of sight. Assuming that DLAs are (proto-)galactic disks and
using detailed chemical evolution models with metallicity dependent yields we
study chemical evolution and dust depletion patterns for alpha and iron-peak
elements in DLAs. When observational constraints on the metal column density of
DLAs are taken into account (as suggested in Boisse et al. 1998) we find that
our models reproduce fairly well the observed mild redshift evolution of the
abundances of 8 elements (Al, Si, S, Cr, Mn, Fe, Zn and Ni) as well as the
observed scatter at a given redshift. By considering the aforementioned
dependence of abundance ratios on metal column density, we further explore the
general dust depletion pattern in DLAs, comparing to our model results and to a
solar reference pattern. We suggest that further measurements of the key
elements, i.e. Zn, S and Mn, will help to gain more insight into the nature of
DLAs. In any case, the presently uncertain nucleosynthesis of Zn in massive
stars (on which a large part of these conclusions is based) should be carefully
scrutinised.Comment: 12 pages, 4 figures, Astronomy and Astrophysics, in pres
{Chemo-spectrophotometric evolution of spiral galaxies: IV. Star formation efficiency and effective ages of spirals
We study the star formation history of normal spirals by using a large and
homogeneous data sample of local galaxies. For our analysis we utilise detailed
models of chemical and spectrophotometric galactic evolution, calibrated on the
Milky Way disc. We find that star formation efficiency is independent of
galactic mass, while massive discs have, on average, lower gas fractions and
are redder than their low mass counterparts; put together, these findings
convincingly suggest that massive spirals are older than low mass ones. We
evaluate the effective ages of the galaxies of our sample and we find that
massive spirals must be several Gyr older than low mass ones. We also show that
these galaxies (having rotational velocities in the 80-400 km/s range) cannot
have suffered extensive mass losses, i.e. they cannot have lost during their
lifetime an amount of mass much larger than their current content of gas+stars.Comment: 11 pages, 8 figures, MNRAS in pres
A SPECTROSCOPIC STUDY OF THE GIANT LOW SURFACE BRIGHTNESS GALAXY MALIN 1
International audienceLow Surface Brightness galaxies (LSBs) represent a significant fraction of galaxies in the nearby universe. However, despite their large fraction, the structure and origin of this class of galaxies is still poorly understood, especially due to the lack of high-resolution kinematics and spectroscopy. Malin 1 is the largest known low surface brightness galaxy to date, the archetype of so-called giant LSBs. We present new results based on spectroscopic observations of Malin 1, using the Hα and [OII]3727 emission lines in order to bring new constraints on the internal dynamics of this galaxy. We have extracted a total of 16 spectra from different regions of Malin 1 and calculated the inner rotational velocities using the observed shift in the emission line wavelengths. We show for the first time a steep rise in the rotation curve of Malin 1 up to ∼400 km s −1 (within r < 10 kpc), which had not been observed in any of the previous works on this galaxy. We will discuss the implications of this result in comparison with existing works on Malin 1 and also the possibility for making a new mass model for this galaxy
Chemo-spectrophotometric evolution of spiral galaxies: V. Properties of galactic discs at high redshift
We explore the implications for the high redshift universe of
``state-of-the-art'' models for the chemical and spectrophotometric evolution
of spiral galaxies. The models are based on simple ``scaling relations'' for
discs, obtained in the framework of Cold Dark Matter models for galaxy
formation, and were ``calibrated'' as to reproduce the properties of the Milky
Way and of nearby discs (at redshift z~0). In this paper, we compare the
predictions of our ``hybrid'' approach to galaxy evolution to observations at
moderate and high redshift. We find that the models are in fairly good
agreement with observations up to z~1, while some problems appear at higher
redshift (provided there is no selection bias in the data); these discrepancies
may suggest that galaxy mergers (not considered in this work) played a non
negligible role at z>1. We also predict the existence of a ``universal''
correlation between abundance gradients and disc scalelengths, independent of
redshift.Comment: 14 pages, 11 figures, MNRAS, in pres
From Spirals to Low Surface Brightness galaxies
We show that simple models of the chemical and spectrophotometric evolution
of galaxies can be used to explore the properties of present-day galaxies and
especially the causes of the observed variety among disc galaxies. We focus on
the link between ``classical'' spirals and Low Surface Brightness galaxies.Comment: 4 pages, To appear in the Proceedings of the Euroconference The
Evolution of Galaxies: III. From simple approaches to self-consistent models
(Kluwer
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