%0 Journal Article
%T Star formation histories of early-type galaxies. I: Higher order Balmer lines as age indicators
%A Nelson Caldwell
%A James A. Rose
%A Kristi Dendy Concannon
%J Physics
%D 2003
%I arXiv
%R 10.1086/375308
%X (shortened) We have obtained blue integrated spectra of 175 nearby early-type galaxies, covering a wide range in galaxy velocity dispersion, and emphasizing those with sigma < 100 km/s. Galaxies have been observed both in the Virgo cluster and in lower-density environments. The main goals are the evaluation of higher order Balmer lines as age indicators, and differences in stellar populations as a function of mass, environment and morphology. In this first paper our emphasis is on presenting the evolutionary population synthesis models. Lower-sigma galaxies exhibit a substantially greater intrinsic scatter, in a variety of line strength indicators, than do higher-sigma galaxies, with the large intrinsic scatter setting in below a sigma of 100 km/s. Modeling of the observed spectral indices indicates that the strong Balmer lines found primarily among the low-sigma galaxies are caused by young age, rather than by low metallicity. Thus we find a trend between the population age and the velocity dispersion, such that low sigma galaxies have younger luminosity-weighted mean ages. We have repeated this analysis using several different Balmer lines, and find consistent results from one spectral indicator to another.
%U http://arxiv.org/abs/astro-ph/0303345v1