SIMBAD references

Near-infrared spectra of 50 elliptical galaxies in the Pisces, Abell 2199 and 2634 clusters, and in the general field, have been obtained. The strength of the CO (2.3-µ m) absorption feature in these galaxies is used to explore the presence of an intermediate-age population (e.g. asymptotic giant branch stars) in ellipticals in different environments. We find that the strongest evidence for such a population comes from ellipticals in groups of a few members, which we interpret as the result of recent minor merging of these galaxies with later-type galaxies. Field galaxies from very isolated environments, on the other hand, show no evidence for young or intermediate-age stars as revealed by Hβ and CO absorptions, and appear to form a very uniform, old population with very little scatter in metallicity and star formation history.