Strong Balmer Lines in Old Ellipticals

Abstract

Because of the wide range of Balmer line strengths observed, elliptical galaxies are usually interpreted to exhibit an appreciable scatter in age. Here we show that Composite Stellar Population models containing an old metal-poor subcomponent simultaneously produce strong Balmer lines and strong metallic lines without invoking a young population. The key to this result is that our SSP models better match the steep increase of Hβ in metal-poor globular clusters than models in the literature. Hence, the scatter of Hβ observed in cluster and luminous field elliptical galaxies can be explained by a spread in the metallicity of old stellar populations. The proposed model is checked against other observational constraints like colors and the flux in the mid-UV.