23 research outputs found
About the Chemical Evolution of dSphs (and the peculiar Globular Cluster Omega Cen)
We present three dimensional hydrodynamical simulations aimed at studying the
dynamical and chemical evolution of the interstellar medium (ISM) in isolated
dwarf spheroidal galaxies (dSphs). This evolution is driven by the explosion of
Type II and Type Ia supernovae, whose different contribution on both the
dynamics and chemical enrichment is taken into account. Radiative losses are
effective in radiating away the huge amount of energy released by SNe
explosions, and the dSph is able to retain most of the gas allowing a long
period (>2-3 Gyr) of star formation, as usually observed in this kind of
galaxies. We are able to reproduce the stellar metallicity distribution
function (MDF) as well as the peculiar chemical properties of strongly
O-depleted stars observed in several dSphs. The model also naturally predicts
two different stellar populations, with an anti-correlation between [Fe/H] and
velocity dispersion, similarly to what observed in the Sculptor and Fornax
dSphs. These results derive from the inhomogeneous pollution of the SNe Ia, a
distinctive characteristic of our model. We also applied the model to the
peculiar globular cluster (GC) Omega Cen in the hypothesis that it is the
remnant of a formerly larger stellar system, possibly a dSph.Comment: To appear in the IAU Symposium 255, "Low-Metallicity Star Formation:
From the First stars to Dwarf Galaxies", contributed talk, 5 page
Chemical evolution of bulges at high redshift
We present a new class of hydrodynamical models for the formation of bulges
(either massive elliptical galaxies or classical bulges in spirals) in which we
implement detailed prescriptions for the chemical evolution of H, He, O and Fe.
Our results hint toward an outside-in formation in the context of the
supernovae-driven wind scenario. The build-up of the chemical properties of the
stellar populations inhabiting the galactic core is very fast. Therefore we
predict a non significant evolution of both the mass-metallicity and the
mass-[alpha/Fe] relations after the first 0.5 - 1 Gyr. In this framework we
explain how the observed slopes, either positive or negative, in the radial
gradient of the mean stellar [alpha/Fe], and their apparent lack of any
correlation with all the other observables, can arise as a consequence of the
interplay between star formation and metal-enhanced internal gas flows.Comment: 4 pages, 6 figures, to appear on the IAU Symposium 245 Proceedings,
Eds. M. Bureau, E. Athanassoula, B. Barbu
Abundance gradient slopes versus mass in spheroids: predictions by monolithic models
We investigate whether it is possible to explain the wide range of observed gradients in early-type galaxies in the framework of monolithic models. To do so, we extend the set of hydrodynamical simulations by Pipino et al. by including low-mass ellipticals and spiral (true) bulges. These models satisfy the mass-metallicity and the mass-[α/Fe] relations. The typical metallicity gradients predicted by our models have a slope of −0.3 dex per decade variation in radius, consistent with the mean values of several observational samples. However, we also find a few quite massive galaxies in which this slope is −0.5 dex per decade, in agreement with some recent data. In particular, we find a mild dependence from the mass tracers when we transform the stellar abundance gradients into radial variations of the Mg2 line-strength index, but not in the Mgb. We conclude that, rather than a mass-slope relation, is more appropriate to speak of an increase in the scatter of the gradient slope with the galactic mass. We can explain such a behaviour with different efficiencies of star formation in the framework of the revised monolithic formation scenario, hence the scatter in the observed gradients should not be used as an evidence of the need of mergers. Indeed, model galaxies that exhibit the steepest gradient slopes are preferentially those with the highest star formation efficiency at that given mas
Evolution of Binary Stars in Multiple-Population Globular Clusters - II. Compact Binaries
We present the results of a survey of N-body simulations aimed at exploring
the evolution of compact binaries in multiple-population globular clusters.We
show that as a consequence of the initial differences in the structural
properties of the first-generation (FG) and the second-generation (SG)
populations and the effects of dynamical processes on binary stars, the SG
binary fraction decreases more rapidly than that of the FG population. The
difference between the FG and SG binary fraction is qualitatively similar to
but quantitatively smaller than that found for wider binaries in our previous
investigations.The evolution of the radial variation of the binary fraction is
driven by the interplay between binary segregation, ionization and ejection.
Ionization and ejection counteract in part the effects of mass segregation but
for compact binaries the effects of segregation dominate and the inner binary
fraction increases during the cluster evolution. We explore the variation of
the difference between the FG and the SG binary fraction with the distance from
the cluster centre and its dependence on the binary binding energy and cluster
structural parameters. The difference between the binary fraction in the FG and
the SG populations found in our simulations is consistent with the results of
observational studies finding a smaller binary fraction in the SG population.Comment: 9 pages, 12 figures. Accepted for publication in MNRA
Evolution of Binary Stars in Multiple-Population Globular Clusters
The discovery of multiple stellar populations in globular clusters has
implications for all the aspects of the study of these stellar systems. In this
paper, by means of N-body simulations, we study the evolution of binary stars
in multiple-population clusters and explore the implications of the initial
differences in the spatial distribution of different stellar populations for
the evolution and survival of their binary stars. Our simulations show that
initial differences between the spatial distribution of first-generation (FG)
and second-generation (SG) stars can leave a fingerprint in the current
properties of the binary population. SG binaries are disrupted more efficiently
than those of the FG population resulting in a global SG binary fraction
smaller than that of the FG. As for surviving binaries, dynamical evolution
produces a difference between the SG and the FG binary binding energy
distribution with the SG population characterized by a larger fraction of high
binding energy (more bound) binaries. We have also studied the dependence of
the binary properties on the distance from the cluster centre. Although the
global binary fraction decreases more rapidly for the SG population, the local
binary fraction measured in the cluster inner regions may still be dominated by
SG binaries. The extent of the differences between the surviving FG and SG
binary binding energy distribution also varies radially within the cluster and
is larger in the cluster inner regions.Comment: 10 pages, 12 figures. Accepted for publication in MNRA