High-Resolution Optical and UV Observations of the Centers of NGC 1316 and NGC 3998 with the Hubble Space Telescope

Abstract

B and UV high-resolution images obtained with the HST FOC reveal centrally increasing surface brightness and UV-bright point sources at the nuclei of the early-type galaxies NGC 1316 and NGC 3998. Model fitting of the surface brightness distribution does not exclude a central flattening, which could however be the result of extinction and/or of improper evaluation of the point-source component. The present data, while not requiring the presence of central massive black holes in these two galaxies, make them possible candidates. Follow-up work is needed to study this point further. The presence of unresolved nuclei gives model- dependent support to this quest, if these sources are due to small AGN. These UV-bright sources could belong to the low-luminosity end of active nuclear emission.