397 research outputs found
Disk galaxy evolution: from the Milky Way to high-redshift disks
We develop a detailed model of the Milky Way (a ``prototypical'' disk galaxy)
and extend it to other disks with the help of some simple scaling relations,
obtained in the framework of Cold Dark Matter models. This phenomenological
(``hybrid'') approach to the study of disk galaxy evolution allows us to
reproduce successfully a large number of observed properties of disk galaxies
in the local Universe and up to redshift z~1. The important conclusion is that,
on average, massive disks have formed the bulk of their stars earlier than
their lower mass counterparts: the ``star formation hierarchy'' has been
apparently opposite to the ``dark matter assembly'' hierarchy. It is not yet
clear whether ``feedback'' (as used in semi-analytical models of galaxy
evolution) can explain that discrepancy.Comment: 12 pages, 8 figures. Invited talk in "Galaxy Evolution III: From
Simple Approaches to Self-Consistent Models" (Kiel, Germany, July 16-20,
2002) Eds. G. Hensler et al., 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
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
Evolution of the Milky Way with radial motions of stars and gas I. The solar neighborhood and the thin and thick disk
We study the role of radial migration of stars on the chemical evolution of
the Milky Way disk. In particular, we are interested in the impact of that
process on the local properties of the disk (age-metallicity relation and its
dispersion, metallicity distribution, evolution of abundance ratios) and on the
morphological properties of the resulting thick and thin disks.We use a model
with several new or up-dated ingredients: atomic and molecular gas phases, star
formation depending on molecular gas, yields from the recent homogeneous grid
provided by Nomoto et al. (2013), observationally inferred SNIa rates. We
describe radial migration with parametrised time- and radius-dependent
diffusion coefficients, based on the analysis of a N-body+SPH simulation. We
also consider parametrised radial gas flows, induced by the action of the
Galactic bar. Our model reproduces well the present day values of most of the
main global observables of the MW disk and bulge, and also the observed
"stacked" evolution of MW-type galaxies from van Dokkum et al. (2013). The
azimuthally averaged radial velocity of gas inflow is constrained to less than
a few tenths of km/s. Radial migration is constrained by the observed
dispersion in the age-metallicity relation. Assuming that the thick disk is the
oldest (>9 Gyr) part of the disk, we find that the adopted radial migration
scheme can reproduce quantitatively the main local properties of the thin and
thick disk. The thick disk extends up to ~11 kpc and has a scale length of 1.8
kpc, considerably shorter than the thin disk, because of the inside-out
formation scheme. We also show how, in this framework, current and forthcoming
spectroscopic observations can constrain the nucleosynthesis yields of massive
stars for the metallicity range of 0.1 solar to 2-3 solar.Comment: 27 pages, 25 figures, accepted for publication in Astronomy and
Astrophysic
Radial migration in a bar-dominated disk galaxy I: Impact on chemical evolution
We study radial migration and chemical evolution in a bar-dominated disk
galaxy, by analyzing the results of a fully self-consistent, high resolution
N-body+SPH simulation. We find different behaviours for gas and star particles.
Gas within corotation is driven in the central regions by the bar, where it
forms a pseudo-bulge (disky-bulge), but it undergoes negligible radial
displacement outside the bar region. Stars undergo substantial radial migration
at all times, caused first by transient spiral arms and later by the bar.
Despite the important amount of radial migration occurring in our model, its
impact on the chemical properties is limited. The reason is the relatively flat
abundance profile, due to the rapid early evolution of the whole disk. We show
that the implications of radial migration on chemical evolution can be studied
to a good accuracy by post-processing the results of the N-body+SPH calculation
with a simple chemical evolution model having detailed chemistry and a
parametrized description of radial migration. We find that radial migration
impacts on chemical evolution both directly (by moving around the long-lived
agents of nucleosynthesis, like e.g. SNIa or AGB stars, and thus altering the
abundance profiles of the gas) and indirectly (by moving around the long-lived
tracers of chemical evolution and thus affecting stellar metallicity profiles,
local age-metallicity relations and metallicity distributions of stars, etc.).Comment: 13 pages, 16 figures, MNRAS in pres
The chemical evolution of the Milky Way in a cosmological context
A short overview is presented of several topics concerning the evolution of
the Milky Way (MW) in a cosmological context. In particular, the metallicity
distribution of the MW halo is derived analytically and the halo metallicity
and abundance patterns are compared to those of Local Group galaxies. The
inside-out formation of the MW disk is supported by the observed evolution of
the abundance gradients, while their magnitude suggests that the role of the
Galactic bar has been negligible. Finally, the empirical foundations
(age-metallicity relation and metallicity distribution) of the evolution of the
solar neighborhood, which is the best studied galactic sub-system, have been
seriously questioned recently.Comment: 12 pages, 17 figures. Invited review at CRAL-Conference Series I
"Chemodynamics: from first stars to local galaxies" (Lyon 10-14 July 2006),
Eds. Emsellem, Wozniak, Massacrier, Gonzalez, Devriendt, Champavert, EAS
Publications Serie
Perspectives in Galactic Chemical Evolution studies
In this review I focus on a few selected topics, where recent theoretical and/or observational progress has been made and important developments are expected in the future. They include: 1) Evolution of isotopic ratios, 2) Mixing processes and dispersion in abundance ratios, 3) Abundance gradients in the Galactic disk (and abundance patterns in the inner Galaxy), 4) The question of primary Nitrogen and 5) Abundance patterns in extragalactic damped Lyman-alpha systems (DLAs)
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