Supernova progenitors and iron density evolution from SN rate evolution measurements

Using an extensive compilation of literature supernova rate data we study to which extent its evolution constrains the star formation history, the distribution of the type Ia supernova (SNIa) progenitor's lifetime, the mass range of core-collapse supernova (CCSN) progenitors, and the evolution of the iron density in the field. We find that the diagnostic power of the cosmic SNIa rate on their progenitor model is relatively weak. More promising is the use of the evolution of the SNIa rate in galaxy clusters. We find that the CCSN rate is compatible with a Salpeter IMF, with a minimum mass for their progenitors > 10 Msun. We estimate the evolution in the field of the iron density released by SNe and find that in the local universe the iron abundance should be ~ 0.1 solar. We discuss the difference between this value and the iron abundance in clusters.Comment: Accepted for publication in New Astronom

Correlation of the rate of Type Ia supernovae with the parent galaxy properties: Light and shadows

The identification of the progenitors of Type Ia Supernovae (SNIa) is extremely important in several astrophysical contexts, ranging from stellar evolution in close binary systems to evaluating cosmological parameters. Determining the distribution of the delay times (DTD) of SNIa progenitors can shed light on their nature. In this paper we investigate on the diagnostic capabilities on the DTD of the correlation between the SNIa rate and the parent galaxy properties by examining its systematics with the various parameters at play: simple stellar population models, the adopted description for the star formation history in galaxies, and the way in which the masses of the galaxies are evaluated. We compute models for the correlations of the SNIa rate with the parent galaxy color and specific star formation rate for a variety of input ingredients, and for a few astrophysically motivated DTD laws. The models are compared to the results of three independent observational surveys. We find that the scaling of the SNIa rate with the properties of the parent galaxy is sensitive to all input ingredients mentioned above. This is a severe limitation on the possibility to discriminate alternative DTDs. In addition, current surveys show some discrepancies for the rate measured in the reddest and bluest galaxies, likely due to limited statistics and inhomogeneity of the observations. For galaxies with intermediate colors the rates are in agreement, leading to a robust determination of the productivity of SNIa from stellar populations of $\simeq$ 0.8 events per 1000 \msun. Large stastistics of SNIa events along with accurate measurements of the star formation history in the galaxies are required to derive firm constraints on the DTD. LSST will achieve these results by providing the homogeneous, unbiased and vast database on both SNIa and galaxies.Comment: Astronomy and Astrophysics in press. Includes one more figure in the appendix. Notice the slight change of titl

Constraints on galaxy formation from alpha-enhancement in luminous elliptical galaxies

We explore the formation of alpha-enhanced and metal-rich stellar populations in the nuclei of luminous ellipticals under the assumption of two extreme galaxy formation scenarios based on hierarchical clustering, namely a fast clumpy collapse and the merger of two spirals. We investigate the parameter space of star formation time-scale, IMF slope, and stellar yields. In particular, the latter add a huge uncertainty in constraining time-scales and IMF slopes. We find that -- for Thielemann, Nomoto & Hashimoto nucleosynthesis -- in a fast clumpy collapse scenario an [alpha/Fe] overabundance of approx. 0.2 dex in the high metallicity stars can be achieved with a Salpeter IMF and star formation time-scales of the order 10^9 yr. The scenario of two merging spirals which are similar to our Galaxy, instead, fails to reproduce alpha-enhanced abundance ratios in the metal-rich stars, unless the IMF is flattened during the burst ignited by the merger. This result is independent of the burst time-scale. We suggest that abundance gradients give hints to distinguish between the two extreme formation scenarios considered in this paper.Comment: Accepted for publication in MNRAS, LaTex 2.09 with mn.sty, 13 pages, 5 figure

On the metallicity distribution in the nuclei of elliptical galaxies

Using current models of spectrophotometric properties of single age, single metallicity stellar populations I have computed the Mg2, Hbeta, Fe52 and Fe53 line strengths for stellar populations with a metallicity spread. The comparison of these models with the nuclear indices of early type galaxies yield the following major conclusions. The metallicity distribution of the closed box, simple model for the chemical evolution of galaxies is not able to account for Mg2 and Fe52, Fe53 values in excess of 0.27,3 and 2.7, respectively, which are observed in the nuclei of a large fraction of Ellipticals. To reproduce the line strengths in these galaxies high average metallicities, small metallicity dispersion and old ages are required. In particular, Mg2 values of 0.3 are reproduced only with a metallicity distribution ranging from 0.5\Zsun to 3\Zsun, and 15 Gyr old stellar populations. I interpret the data as indicating that the gas out of which the nuclei of ellipticals formed was pre-enriched, to larger metallicities for increasing \Mgtw.The presence of a metallicity dispersion does not alter the relation between Mg2 and Iron indices with respect to the SSP models. Thus, the need for a Mg/Fe overabundance in the strongest lined galaxies is confirmed, and I present a simple way to estimate the [Mg/Fe] ratio on the basis of existing models with solar abundance ratios.Comment: 16 pages, Latex File+mnrasl.sty, 8 Postscript figures, to appear in MNRA

Studying stellar halos with future facilities

Stellar halos around galaxies retain fundamental evidence of the processes which lead to their build up. Sophisticated models of galaxy formation in a cosmological context yield quantitative predictions about various observable characteristics, including the amount of substructure, the slope of radial mass profiles and three dimensional shapes, and the properties of the stellar populations in the halos. The comparison of such models with the observations provides constraints on the general picture of galaxy formation in the hierarchical Universe, as well as on the physical processes taking place in the halos formation. With the current observing facilities, stellar halos can be effectively probed only for a limited number of nearby galaxies. In this paper we illustrate the progress that we expect in this field with the future ground based large aperture telescopes (E-ELT) and with space based facilities as JWST.Comment: 6 pages, 4 figures, to appear in Proc. IAU Symposium 317 "The General Assembly of Stellar Halos: Structure, Origin and Evolution.