An empirical connection between the ultraviolet color of early-type galaxies and the stellar initial mass function

Abstract

Using new UV magnitudes for a sample of early-type galaxies (ETGs) with published stellar mass-to-light ratios, Υ_*, we find a correlation between UV color and Υ_* that is tighter than those previously identified between Υ_* and either the central stellar velocity dispersion, metallicity, or alpha enhancement. The sense of the correlation is that galaxies with larger Υ_* are bluer in the UV. We conjecture that differences in the lower mass end of the stellar initial mass function (IMF) are related to the nature of the extreme horizontal branch populations that are generally responsible for the UV flux in ETGs. If so, then UV color can be used to identify ETGs with particular IMF properties and to estimate Υ_*.