A NEW CHEMO-EVOLUTIONARY POPULATION SYNTHESIS MODEL FOR EARLY-TYPE GALAXIES .2. OBSERVATIONS AND RESULTS

We present the results of applying a new chemo-evolutionary stellar po pulation model, developed in a previous paper, to new high-quality obs ervational data of the nuclear regions of two representative elliptica l galaxies and the bulge of the Sombrero galaxy. Here we fit in detail similar to 20 absorption lines and six optical and near-infrared colo rs, following two approaches: fitting a single-age, single-metallicity model and fitting our full chemical evolutionary model. We find that all the iron lines are weaker than the best-fitting models predict, in dicating that the iron abundance is anomalous and deficient. We also f ind that the Ca I index at 4227 Angstrom is much lower than predicted by the models. We can obtain good fits for all the other lines and obs erved colors with models of old and metal-rich stellar populations and can show that the observed radial gradients are due to metallicity de creasing outward. We find that good fits are obtained both with fully evolutionary models and with single-age, single-metallicity models. Th is is due to the fact that in the evolutionary model more than 80% of the stars form within 1.5 Gyr after the formation of the galaxies. The fact that slightly better fits are obtained with evolutionary models indicates that these galaxies contain a small spread in metallicity.