Seyfert Galaxies. IV. Nuclear Profiles of Markarian Seyfert Galaxies from Hubble Space Telescope Images

Abstract

We have examined the nuclear profiles of the Seyfert and non-Seyfert Markarian galaxies in our near-infrared Hubble Space Telescope WF/PC-1 snapshot survey. We find that nuclei of types 1-1.5 Seyfert galaxies are dominated by strong point sources, while those of Seyfert 2 and non- Seyfert Markarian galaxies tend to be resolved, less distinguished, and similar in shape to normal galaxy luminosity profiles. Two possible interpretations of this result for type 2 Seyfert galaxies are that their nuclear continuum sources are undetected in our bandpass, contributing less than 10% of the nuclear light (within 0.5 radius) in all cases or that their nuclear components are resolved and blend in smoothly with the brightness profile of the host galaxy's bulge. Since spectroscopic studies support typical nuclear continuum fractions distinctly greater than 10%, the latter conclusion is clearly preferable. If the continua observed in Seyfert 2 galaxies originate as nuclear light that is redirected into the line of sight by scattering, as predicted by unified models of active galactic nuclei, then the scattering regions must be extended. Simple simulations suggest that these regions must cover several tens of parsecs or more, in agreement with estimates of the sizes of the scattering "mirrors" in other Seyfert 2 galaxies. However, the similarity of the profiles of non-Seyfert Markarian and type 2 Seyfert nuclei suggests that circumnuclear star formation may also be an important component in the nuclear profiles of the latter.