arXiv subjects

Antonio Pipino

Publications and source records attributed to Antonio Pipino.

24 records · Page 2Linked to original sources

arXiv2004

The effects of population III stars on the chemical and photometrical evolution of ellipticals

We have studied the effects of an hypothetical initial generation containing very massive stars (M > 100 Msun, pair-creation SNe) on the chemical and photometric evolution of elliptical galaxies. To this purpose, we have computed the evolution of a typical elliptical galaxy with luminous mass of the order of 10^11 Msun and adopted chemical evolution models already tested to reproduce the main features of ellipticals. We have tested several sets of yields for very massive zero-metallicity stars: these stars should produce quite different amounts of heavy elements than lower mass stars. We found that the effects of population III stars on the chemical enrichment is negligible if only one or two generations of such stars occurred, whereas they produce quite different results from the standard models if they continuously formed for a period not shorter than 0.1 Gyr. In this case, the results are at variance with the main observational constraints of ellipticals such as the average [ ] ratio in stars and the integrated colors. Therefore, we conclude that if population III stars ever existed they must have been present for a very short period of time and their effects on the following evolution of the parent galaxy must have been negligible. This effect is minimum if a more realistic model with initial infall of gas rather than the classic monolithic model is adopted. Ultimately, we conclude that there is no need to invoke a generation of very massive stars in ellipticals to explain their chemical and photometric properties.

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arXiv2003

Photo-Chemical Evolution of Elliptical Galaxies I. The high-redshift formation scenario

In this paper we compute new multi-zone photo-chemical evolution models for elliptical galaxies, taking into account detailed nucleosynthetic yields, feedback from supernovae and an initial infall episode. By comparing model predictions with observations, we derive a picture of galaxy formation in which the higher is the mass of the galaxy, the shorter are the infall and the star formation timescales. Therefore, in this scenario, the most massive objects are older than the less massive ones, in the sense that larger galaxies stop forming stars at earlier times. Each galaxy is created outside-in, i.e. the outermost regions accrete gas, form stars and develop a galactic wind very quickly, compared to the central core in which the star formation can last up to ~1.3 Gyr. In particular, we suggest that both the duration of the star formation and the infall timescale decrease with galactic radius. (abridged) By means of our model, we are able to match the observed mass-metallicity and color-magnitude relations for the center of the galaxies as well as to reproduce the overabundance of Mg relative to Fe, observed in the nuclei of bright ellipticals, and its increase with galactic mass. Furthermore, we find that the observed Ca underabundance relative to Mg can be real, due to the non-neglibile contribution of type Ia SN to the production of this element. We predict metallicity and color gradients inside the galaxies which are in good agreement with the mean value of the observed ones. (abridged)

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arXiv2003

Modelling the nova rate in galaxies

We compute theoretical nova rates as well as type Ia SN rates in galaxies of different morphological type (Milky Way, ellipticals and irregulars) by means of detailed chemical evolution models, and compare them with the most recent observations. The main difference among the different galaxies is the assumed history of star formation. In particular, we predict that the nova rates in giant ellipticals such as M87 are 100-300 nova/yr, about a factor of ten larger than in our Galaxy (25 nova/yr), in agreement with very recent estimates from HST data. The best agreement with the observed rates is obtained if the recurrence time of novae in ellipticals is assumed to be longer than in the Milky Way. This result indicates that the star formation rate in ellipticals, and in particular in M87, must have been very efficient at early cosmic epochs. We predict a nova rate for the LMC of 1.7 nova/yr, again in agreement with observations. We compute also the K- and B-band luminosities for ellipticals of different luminous mass and conclude that there is not a clear trend for the luminosity specific nova rate with luminosity among these galaxies. However, firm conclusions about ellipticals cannot be drawn because of possible observational biases in observing these objects. The comparison between the specific nova rates in the Milky Way and the LMC indicates a trend of increasing nova rate passing from the Galaxy towards late-type spirals and Magellanic irregulars.

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arXiv2002

Chemical evolution of Elliptical Galaxies and the ICM

We present a new model for the chemical evolution of elliptical galaxies taking into account SN feedback, detailed nucleosynthesis and galactic winds. We discuss the effect of galactic winds on the chemical enrichment of the ICM and compute the energy per particle injected by the galaxies into the ICM.

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arXiv2002

Outflows from ellipticals: the role of supernovae

Models of SN driven galactic winds for ellipticals are presented. We assume that ellipticals formed at high redshift and suffered an intense burst of star formation. The role of supernovae of type II and Ia in the chemical enrichment and in triggering galactic winds is studied. In particular, several recipes for SN feed-back together with detailed nucleosynthesis prescriptions are considered. It is shown that SNe of type II have a dominant role in enriching the interstellar medium of elliptical galaxies whereas type Ia SNe dominate the enrichment and the energetics of the intracluster medium.

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arXiv2002

SNe heating and the chemical evolution of the intra-cluster medium

We compute the chemical and thermal history of the intra-cluster medium in rich and poor clusters under the assumption that supernovae (I, II) are the major responsible both for the chemical enrichment and the heating of the intra-cluster gas. We assume that only ellipticals and S0 galaxies contribute to the enrichment and heating of the intra-cluster gas through supernova driven winds and explore several prescriptions for describing the feed-back between supernovae and the interstellar medium in galaxies. We integrate then the chemical and energetical contributions from single cluster galaxies over the cluster luminosity function and derive the variations of these quantities as functions of the cosmic time. We reach the following conclusions: i) while type II supernovae dominates the chemical enrichment and energetics inside the galaxies, type Ia supernovae play a predominant role in the intra-cluster medium, ii) galaxy models, which reproduce the observed chemical abundances and abundance ratios in the intra-cluster medium, predict a maximum of 0.3-0.4 keV per particle of energy input, a result obtained by assuming that type Ia supernovae contribute 100% of their initial blast wave energy whereas type II supernovae contribute only by a few percents of their initial energy.

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