The Central Regions of Early-Type Galaxies Hosting Active Galactic Nuclei as Viewed with HST/NICMOS

Abstract

We present preliminary results from surface photometry of a sample of early-type galaxies observed with NICMOS on board HST in the F160W (H-band) filter. Dust is found to occur mostly in galaxies which possess unresolved nuclei, and in a few cases the presence of dust causes the isophotes to appear boxy. We performed a 2-D modeling of the host galaxy light distribution using the empirical Nuker function, which proves to be an adequate representation of the surface-brightness profile for most early-type galaxies. The accurate modeling of the bulge light allows us to obtain the magnitude of the unresolved central source without contamination from the underlying stellar population. Our classification of early-type galaxies into core-type and power-law galaxies agrees with the results from previous work based on HST optical images, with core profiles occurring in luminous galaxies and power-law profiles occurring in low-luminosity galaxies with disky isophotes. We do not find a clear dichotomy in the distribution of inner slopes. Unresolved nuclear point sources are evident in about one-third of the sample galaxies, with H magnitudes in the range 13.5 to 17.3. Most of the type 1 Seyfert and LINER nuclei (83%) reveal a distinct point source, while the detection rate is much less for type 2 nuclei (35%). The occurrence of point sources appears to be independent of whether the underlying galaxy has core-type profile or power-law profile.