HST STIS Spectra of Nuclear Star Clusters in Spiral Galaxies
Publication date: 15 Sep 2006
Authors: Rossa, J., et al.
Journal: The Astronomical Journal
Copyright: The American Astronomical SocietyWe study the nuclear star clusters in spiral galaxies of various Hubble types using spectra obtained with STIS on-board HST. We observed the nuclear clusters in 40 galaxies, selected from two previous HST/WFPC2 imaging surveys. At a spatial resolution of about 0.2", the spectra provide a better separation of cluster light from underlying galaxy light than is possible with ground-based spectra. Approximately half of the spectra have sufficient signal-to-noise ratio for detailed stellar population analysis. For the other half we only measure the continuum slope, as quantified by the B-V color. To infer the star formation history, metallicity and dust extinction, we fit weighted superpositions of single-age stellar population templates to the high signal-to-noise spectra. We use the results to determine the luminosity-weighted age, mass-to-light ratio, and masses of the clusters. The models provide excellent fits to the data and generally require a mixture of populations of different ages. Approximately half of the sample clusters contain a population younger than 1 Gyr.