Synthetic colors and the chemical evolution of elliptical galaxies

Abstract

Detailed photometric and chemical evolution models for elliptical galaxies of various initial masses are presented. The observed color-magnitude diagrams and the mass-metallicity relation are well reproduced. In particular, the mass-metallicity relation is obtained by computing the detailed evolution of the abundances of Fe. Particular attention is given to interpreting the UV excess observed in ellipticals and its behavior as a function of the metal content of these galaxies. It is suggested that the UV excess in ellipticals is determined mainly by metal-rich stars, which do not experience any thermal pulsing phase during their advanced evolution following the horizontal branch phase and which leave the AGB well before the onset or the thermal pulses. It is shown that this scenario is well-grounded, and that above a critical metallicity the masses of the stars in the post-early AGB phase are lower for larger metallicities. 76 refs.