An atlas of the circumnuclear regions of 75 Seyfert galaxies in the near-ultraviolet with the Hubble Space Telescope advanced camara for surveys

Abstract

We present an atlas of the central regions of 75 Seyfert galaxies imaged in the near-UV with the Advanced Camera for Surveys of the Hubble Space Telescope at an average resolution of ~10 pc. These data complement archival high resolution data from the Hubble Space Telescope at optical and near-IR wavelengths, creating an extremely valuable data set for astronomers with a broad range of scientific interests. Our goal is to investigate the nature of the near-UV light in these objects, its relation to the circumnuclear starburst phenomenon, and the connection of this to the evolution and growth of the galaxy bulge and central black hole. In this paper we describe the near-UVmorphology of the objects and characterize the near-UVemission. We estimate the size and the luminosity of the emitting regions and extract the luminosity profile. We also determine the presence of unresolved compact nuclei. In addition, the circumnuclear stellar cluster population is identified, and the contribution of the stellar clusters to the total light, at this wavelength, is estimated. The size of the sample allows us to draw robust statistical conclusions.We find that Seyfert 1 galaxies (Sy1’s) are completely dominated by their bright and compact nuclei, which remains pointlike at this resolution, while we find almost no unresolved nuclei in Seyfert 2 galaxies (Sy2’s). The Seyfert types 1 and 2 are quite segregated in an asymmetry versus compactness plot. Stellar clusters are found somewhat more frequently in Sy2’s (in ~70% of the galaxies) than in Sy1’s (~57%), and contribute more to the total light in Sy2’s, but these two differences seem to be mostly due to the large contribution of the compact nuclei in Sy1’s, as the luminosity distribution of the clusters is similar in both Seyfert types.