Disentangling Nitrogen and Carbon Abundances in Early-Type Galaxies

The near-UV NH3360 feature has been measured in a sample of 35 early-type galaxies in a wide range of masses and environments. We found that, contrary to what is seen with Mg- and C-sensitive Lick-style indices, NH3360 does not vary significantly with galaxy velocity dispersion. When compared with solar-scaled stellar population models N/Fe appears mildly enhanced. We do not detect any difference in the NH3360 index between galaxies in different environments. We outline the important implications of these conclusions for our understanding of the origin of carbon and nitrogen, and the star formation histories of early-type galaxies.