Nuclear Properties of a Sample of Nearby Spiral Galaxies fromHubble Space TelescopeSTIS Imaging

We present surface photometry for the central regions of a sample of 48spiral galaxies (mostly unbarred and barred of types Sbc or Sc) observed withthe Space Telescope Imaging Spectrograph on board the Hubble Space Telescope.Surface brightness profiles were derived and modeled with a Nuker law. We alsoanalyzed archival Wide Field Planetary Camera~2 images with a larger field ofview, available for 18 galaxies in our sample. We modeled the extracted bulgesurface brightness profiles with an exponential, a de Vaucouleurs or a Sersicprofile. In agreement with previous studies, we find that bulges of Sbcgalaxies fall into two categories: bulges well described by an exponentialprofile and those well described by an de Vaucouleurs profile. Only one galaxyrequires the use of a more general Sersic profile to properly describe thebulge. Nuclear photometrically distinct components are found in ~55% of thegalaxies. For those that we classify as star clusters based on their resolvedextent we find absolute magnitudes that are brighter on average than thosepreviously identified in spiral galaxies. This might be due to a bias in oursample toward star forming galaxies, combined with a trend for star forminggalaxies to host brighter central clusters.Comment: 33 pages, 7 figures. Accepted for publication on the Astronomical Journa