Star Formation in the Nuclei of Spiral Galaxies

Recent observations with the Hubble Space Telescope (HST) have revealed that a large fraction of late-type (Sc and later) spiral galaxies harbor a bright, compact stellar cluster in their dynamical centers. Statistics of the mass, age, and star formation history of these clusters as a function of their host galaxy's Hubble type can be used to constrain models of secular galaxy evolution. Since late-type spirals by definition do not possess a prominent bulge, their nuclear clusters are more easily separated from the underlying disk population. Their spectroscopic properties can thus be studied from ground-based observations. Here, I will discuss plans for, and first results of, a program to study a sample of known nuclear clusters in late-type spirals. For one galaxy (IC 342), we have used high-resolution near infrared spectroscopy to determine the cluster mass directly via its stellar velocity dispersion. The analysis conclusively shows a very low mass-to-light ratio for the nuclear cluster in IC 342, indicative of a young cluster age (about 50 Myrs). From probability arguments, this result favors the scenario that such bursts are a recurrent phenomenon in late-type spiral nuclei.