Star Formation in Early‐Type Galaxies11The conference was held in Guanajuanto, Mexico, in 1998 July. Proceedings will be edited by P. Carral and J. Cepa and will be published in the ASP Conference Series.

Abstract

The proceedings of this meeting will provide a great deal of information concerning current views on early-type galaxies, covering a broader perspective than their star formation history (SFH). Throughout the meeting, three questions were continuously posed by the speakers: (1) Do we need a new definition of early-type galaxies? (2) Are normal E galaxies those in clusters or in the field? and (3) Where do all these data fit in? Contrary to early beliefs, the notion that early-type galaxies may belong to different families is gaining increasing support. Observational evidence indicates that there are wide ranges of values allowed for most properties observed in early-type galaxies (e.g., luminosity, radius, density, isophotal shape, brightness profile, central vs. global properties, surface brightness variations, stellar populations, merger and interaction history, etc.). Both age and metallicity seem to vary along the early-type galaxy sequence, with most luminous ellipticals being the oldest and most metal-rich systems. The observed points to a nonhomologous 0.12 0.15 M/L ∝ M –M formation process, with differences in SFH among mergers. More luminous ellipticals may form from mergers of more massive spirals, resulting in higher star formation rates (SFRs) as well as stronger color and metallicity gradients in these systems. Solar scale abundance ratios are inconsistent with the observations: Mg and other a elements are enhanced with respect to solar values. The presence of dark matter, less concentrated than the luminous matter, seems well established in most ellipticals. However, NGC 404 seems to have no dark matter! Early-type galaxies have an ISM that is reminiscent of later types. Hot, warm, cool, and cold gas and dust have been detected in these galaxies. In general, the amount of gas detected is less than expected from stellar evolution during . S0 and pE galaxies show a 45% detection rate of H i 1 H0 (accreted disk?), whereas normal E galaxies show only a 5% detection rate. CO has been detected in 40% of E galaxies, including pE galaxies. The amount of molecular gas in some dE galaxies is higher than expected from their H i content. H i is centrally concentrated in low-mass E-type galaxies but not in gE galaxies. Star formation has been detected in some galaxies with an unusually high central density of H i. In most