On TP-AGB stars and the mass of galaxies

Recent calculations of evolutionary tracks of TP-AGB stars of different mass and metallicity by Marigo et al. (2007) have been incorporated in the Bruzual & Charlot evolutionary population synthesis models. The mass of the stellar population in HUDF galaxies at z from 1 to 3 determined from fits to the spectro-photometric data of these galaxies is 50 to 80% lower than the mass determined from the BC03 models. The ages inferred for these populations are, with exceptions, 40 to 60% of the BC03 estimates.Comment: 7 pages, 4 figures, in Proceedings of the IAU Symposium No. 241 "Stellar populations as building blocks of galaxies", eds. A. Vazdekis and R. Peletier, Cambridge: Cambridge University Press, in pres

Stellar Populations in Normal Galaxies

I describe very briefly the new libraries of empirical spectra of stars covering wide ranges of values of the atmospheric parameters Teff, log g, [Fe/H], as well as spectral type, that have become available in the recent past, among them the HNGSL, MILES, UVES-POP, and Indo-US libraries. I show the results of using the HNGSL to build population synthesis models. These libraries are complementary in spectral resolution and wavelength coverage, and will prove extremely useful to describe spectral features expected in galaxy spectra from the NUV to the NIR.Comment: 6 pages, 4 figures, in Proceedings of the IAU Symposium No. 222 "The Interplay Among Black Holes, Stars, and ISM in Galactic Nuclei", eds. T. Storchi-Bergmann, L.C. Ho, and H.R. Schmitt, Cambridge: Cambridge University Press, 121-12

Modelling the nebular emission from primeval to present-day star-forming galaxies

We present a new model of the nebular emission from star-forming galaxies in a wide range of chemical compositions, appropriate to interpret observations of galaxies at all cosmic epochs. The model relies on the combination of state-of-the-art stellar population synthesis and photoionization codes to describe the ensemble of HII regions and the diffuse gas ionized by young stars in a galaxy. A main feature of this model is the self-consistent yet versatile treatment of element abundances and depletion onto dust grains, which allows one to relate the observed nebular emission from a galaxy to both gas-phase and dust-phase metal enrichment. We show that this model can account for the rest-frame ultraviolet and optical emission-line properties of galaxies at different redshifts and find that ultraviolet emission lines are more sensitive than optical ones to parameters such as C/O abundance ratio, hydrogen gas density, dust-to-metal mass ratio and upper cutoff of the stellar initial mass function. We also find that, for gas-phase metallicities around solar to slightly sub-solar, widely used formulae to constrain oxygen ionic fractions and the C/O ratio from ultraviolet and optical emission-line luminosities are reasonable faithful. However, the recipes break down at non-solar metallicities, making them inappropriate to study chemically young galaxies. In such cases, a fully self-consistent model of the kind presented in this paper is required to interpret the observed nebular emission.Comment: 20 pages, 15 figures, Accepted for publication in MNRA