Nuclei of nearby disk galaxies .1. A Hubble Space Telescope imaging survey

We present deconvolved images of the central regions of 20 nearby disk galaxies, obtained with the original Planetary Camera of the Hubble Space Telescope. The galaxies span a range in Hubble type from SO to Sm. We have measured surface brightness profiles, and inverted these to estimate luminosity-density profiles. Surface brightness profiles in the central regions show a variety of forms, sometimes clearly affected by heavy dust obscuration. All galaxies in the sample earlier than type Sc show a continuing rise in surface brightness up to the resolution limit in the deconvolved images. Later types show shallower slopes, consistent with exponential disks either continuing into the center or else flattening in the central regions. These galaxies often, but not always, exhibit an unresolved nucleus which is likely a dense nuclear star cluster. Luminosity densities in the earlier-type galaxies reach or exceed 10(4) L(.,V) pc(-3), and the nuclei of the later-type galaxies occasionally approach the same level. The dS0 galaxies in our sample have central characteristics most closely resembling the late-type galaxies. A comparison of the central luminosity and central surface brightness of our galaxies with elliptical galaxies and nucleated dwarfs supports an association of late-type disks systems and such dwarfs. (C) 1996 American Astronomical Society.