Strong Balmer Lines in Old Stellar Populations: No Need for Young Ages in Ellipticals?

Comparing models of Simple Stellar Populations (SSP) with observed linestrengths generally provides a tool to break the age-metallicity degeneracy inelliptical galaxies. Due to the wide range of Balmer line strengths observed,ellipticals have been interpreted to exhibit an appreciable scatter in age. Inthis paper, we analyze Composite Stellar Population models with a simple mix ofan old metal-rich and an old metal-poor component. We show that these modelssimultaneously produce strong Balmer lines and strong metallic lines withoutinvoking a young population. The key to this result is that our models arebased on SSPs that better match the steep increase of Hbeta in metal-poorglobular clusters than models in the literature. Hence, the scatter of Hbetaobserved in cluster and luminous field elliptical galaxies can be explained bya spread in the metallicity of old stellar populations. We check our model withrespect to the so-called G-dwarf problem in ellipticals. For a galaxy subsamplecovering a large range in UV-V colors we demonstrate that the addition of anold metal-poor subcomponent does not invalidate other observational constraintslike colors and the flux in the mid-UV.Comment: Accepted for publication in ApJ Main Journal, 9 pages, 5 figure