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A. M. N. Ferguson, J. M. van der Hulst (Kapteyn Institute, Groningen), J. H. van Gorkom (Columbia University, New York)
Although the star formation properties of disk galaxies across the Hubble sequence are now well-documented, there remains a paucity of information about the frequency and nature of star formation in the earliest types of galaxies, namely the ellipticals/S0s. Long thought to be old, quiescent systems, evidence has steadily been mounting to suggest that a large fraction of present-day field ellipticals/S0s actually contain substantial amounts of cold interstellar gas -- ie. the raw material for star formation.
We present the first results from a deep, narrow-band search for star formation in a sample of ~40 ellipticals and S0s known to have extended cold gas (HI and/or CO) distributions. Some of the galaxies in our sample exhibit peculiar optical features on deep broadband images (eg. faint stellar shells and/or tidal tails) while others look remarkably unperturbed. A wide variety of ionized gas morphologies is seen, ranging from systems with very active star-forming disks (akin to Cen A), to systems with a few isolated faint HII regions to systems with no detectable star formation at all. We discuss the implications of our findings for understanding both galactic star formation, and the evolution of early-type galaxies.