A new chemo-evolutionary population synthesis model for early-type galaxies. II: Observations and Results

Abstract

We present here the results of applying a new chemo-evolutionary stellar population model developed by ourselves in a previous paper (Vazdekis et al. 1996) to new high quality observational data of the nuclear regions of two representative elliptical galaxies and the bulge of the Sombrero galaxy. Here we fit in detail about 20 absorption lines and 6 optical and near-infrared colors following two approaches: fitting a single-age single-metallicity model and fitting our full chemical evolutionary model. We find that all of the iron lines are weaker than the best fitting models predict, indicating that the iron-abundance is anomalous and deficient. We also find that the Ca_I index at 4227 A is much lower than predicted by the models. We can obtain good fits for all the other lines and observed colors with models of old and metal-rich stellar populations, and can show that the observed radial gradients are due to metallicity decreasing outward. We find that good fits are obtained both with fully evolutionary models and with single-age single-metallicity models. This is due to the fact that in the evolutionary model more than 80% of stars form with in 1.5 Gyr after the formation of the galaxies. The fact that slightly better fits are obtained with evolutionary models indicates these galaxies contain a small spread in metallicity.