783 research outputs found
Stellar haloes in Milky-Way mass galaxies: From the inner to the outer haloes
We present a comprehensive study of the chemical properties of the stellar
haloes of Milky-Way mass galaxies, analysing the transition between the inner
to the outer haloes. We find the transition radius between the relative
dominance of the inner-halo and outer-halo stellar populations to be ~15-20 kpc
for most of our haloes, similar to that inferred for the Milky Way from recent
observations. While the number density of stars in the simulated inner-halo
populations decreases rapidly with distance, the outer-halo populations
contribute about 20-40 per cent in the fiducial solar neighborhood, in
particular at the lowest metallicities. We have determined [Fe/H] profiles for
our simulated haloes; they exhibit flat or mild gradients, in the range
[-0.002, -0.01 ] dex/kpc. The metallicity distribution functions exhibit
different features, reflecting the different assembly history of the individual
stellar haloes. We find that stellar haloes formed with larger contributions
from massive subgalactic systems have steeper metallicity gradients. Very
metal-poor stars are mainly contributed to the halo systems by lower-mass
satellites. There is a clear trend among the predicted metallicity distribution
functions that a higher fraction of low-metallicity stars are found with
increasing radius. These properties are consistent with the range of behaviours
observed for stellar haloes of nearby galaxies.Comment: 11 pages, 6 figures. Accepted MNRAS. Revised version after referee's
comment
Fingerprints of the Hierarchical Building up of the Structure on the Mass-Metallicity Relation
We study the mass-metallicity relation of galactic systems with stellar
masses larger than 10^9 Mo in Lambda-CDM scenarios by using chemical
hydrodynamical simulations. We find that this relation arises naturally as a
consequence of the formation of the structure in a hierarchical scenario. The
hierarchical building up of the structure determines a characteristic stellar
mass at M_c ~10^10.2 Moh^-1 which exhibits approximately solar metallicities
from z ~ 3 to z=0. This characteristic mass separates galactic systems in two
groups with massive ones forming most of their stars and metals at high
redshift. We find evolution in the zero point and slope of the mass-metallicity
relation driven mainly by the low mass systems which exhibit the larger
variations in the chemical properties. Although stellar mass and circular
velocity are directly related, the correlation between circular velocity and
metallicity shows a larger evolution with redshift making this relation more
appropriate to confront models and observations. The dispersion found in both
relations is a function of the stellar mass and reflects the different
dynamical history of evolution of the systems.Comment: 4 pages, 4 figures. Accepted MNRAS Letter
The Spatial Distribution of the Galactic First Stars II: SPH Approach
We use cosmological, chemo-dynamical, smoothed particle hydrodynamical
simulations of Milky-Way-analogue galaxies to find the expected present-day
distributions of both metal-free stars that formed from primordial gas and the
oldest star populations. We find that metal-free stars continue to form until
z~4 in halos that are chemically isolated and located far away from the biggest
progenitor of the final system. As a result, if the Population III initial mass
function allows stars with low enough mass to survive until z=0 (< 0.8 Msol),
they would be distributed throughout the Galactic halo. On the other hand, the
oldest stars form in halos that collapsed close to the highest density peak of
the final system, and at z=0 they are located preferentially in the central
region of the Galaxy, i.e., in the bulge. According to our models, these trends
are not sensitive to the merger histories of the disk galaxies or the
implementation of supernova feedback. Furthermore, these full hydrodynamics
results are consistent with our N-body results in Paper I, and lend further
weight to the conclusion that surveys of low-metallicity stars in the Galactic
halo can be used to directly constrain the properties of primordial stars. In
particular, they suggest that the current lack of detections of metal-free
stars implies that their lifetimes were shorter than a Hubble time, placing
constraints on the metal-free initial mass function.Comment: Accepted by ApJ. Emulate ApJ styl
Early Enrichment of the Intergalactic Medium and its Feedback on Galaxy Formation
Supernova-driven outflows from early galaxies may have had a large impact on
the kinetic and chemical structure of the intergalactic medium (IGM). We use
three-dimensional Monte Carlo cosmological realizations of a simple linear
peaks model to track the time evolution of such metal-enriched outflows and
their feedback on galaxy formation. We find that at most 30% of the IGM by
volume is enriched to values above 10^-3 solar in models that only include
objects that cool by atomic transitions. The majority of enrichment occurs
relatively early (5 < z < 12) and resulting in a mass-averaged cosmological
metallicity between 10^-3 and 10^-1.5 solar. The inclusion of Population III
objects that cool through H2 line emission has only a minor impact on these
results: increasing the mean metallicity and filling factor by at most a factor
of 1.4, and moving the dawn of the enrichment epoch to a redshift of
approximately 14 at the earliest. Thus enrichment by outflowing galaxies is
likely to have been incomplete and inhomogeneous, biased to the areas near the
starbursting galaxies themselves. Models with a 10% star formation efficiency
can satisfactorily reproduce the nearly constant (2 < z < 5, Z approximately
3.5 x 10^-4 solar) metallicity of the low column density Ly-alpha forest
derived by Songaila (2001), an effect of the decreasing efficiency of metal
loss from larger galaxies. Finally, we show that IGM enrichment is intimately
tied to the ram-pressure stripping of baryons from neighboring perturbations.
This results in the suppression of at least 20% of the dwarf galaxies in the
mass range 10^8.5 to 10^9.5 solar, in all models with filling factors greater
than 2%, and an overall suppression of approximately 50% of dwarf galaxies in
the most observationally-favored model.Comment: 8 pages, 5 figures, accepted to Ap
The role of tidal interactions in driving galaxy evolution
We carry out a statistical analysis of galaxy pairs selected from chemical
hydrodynamical simulations with the aim at assessing the capability of
hierarchical scenarios to reproduce recent observational results for galaxies
in pairs. Particularly, we analyse the effects of mergers and interactions on
the star formation (SF) activity, the global mean chemical properties and the
colour distribution of interacting galaxies. We also assess the effects of
spurious pairs.Comment: to appear in "Groups of galaxies in the nearby Universe" ESO
Workshop, (Dec 2005) Santiago, Chil
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