HST/STIS results on nuclear star clusters in spiral galaxies

Recent HST imaging surveys have revealed the presence of central star clusters in a majority of spiral galaxies. These nuclear clusters (NCs) may provide important clues to the central structure and secular evolution of disk galaxies. However, their origin and nature are not entirely understood. We therefore performed a spectroscopic survey with HST/STIS of NCs in 40 early- and late-type spiral galaxies. To study the ages and physical properties of the clusters we performed stellar population synthesis modeling using Bruzual-Charlot template spectra. The luminosity-weighted NC ages are almost always less than a Hubble time, indicating that star formation is an ongoing process in spiral galaxy centers. We find that NCs in late-type spirals are younger and less massive than those in early-type spirals