The multitude of unresolved continuum sources at 1.6 microns in Hubble space telescope images of Seyfert galaxies.
QUILLEN A.C., McDONALD C., ALONSO-HERRERO A., LEE A., SHAKED S., RIEKE M.J. and RIEKE G.H.
Abstract (from CDS):
We examine 112 Seyfert galaxies observed by the Hubble Space Telescope at 1.6 µm. We find that ∼50% of the Seyfert 2.0 galaxies which are part of the Revised Shapely-Ames (RSA) Catalog or the CfA redshift sample contain unresolved continuum sources at 1.6 µm. All but a couple of the Seyfert 1.0-1.9 galaxies display unresolved continuum sources. The unresolved sources have fluxes of order 1 mJy, near-infrared luminosities of order 1041 ergs.s–1, and absolute magnitudes MH~-16. Comparison non-Seyfert galaxies from the RSA Catalog display significantly fewer (∼20%), somewhat lower luminosity nuclear sources, which could be due to compact star clusters. We find that the luminosities of the unresolved Seyfert 1.0-1.9 sources at 1.6 µm are correlated with [O III] λ5007 and hard X-ray luminosities, implying that these sources are nonstellar. Assuming a spectral energy distribution similar to that of a Seyfert 2 galaxy, we estimate that a few percent of local spiral galaxies contain black holes emitting as Seyferts at a moderate fraction, ∼10–1-10–4, of their Eddington luminosities. We find no strong correlation between 1.6 µm fluxes and hard X-ray or [O III] λ5007 fluxes for the pure Seyfert 2.0 galaxies. These galaxies also tend to have lower 1.6 µm luminosities compared to the Seyfert 1.0-1.9 galaxies of similar [O III] luminosity. Either large extinctions (AV∼20-40) are present toward their continuum-emitting regions or some fraction of the unresolved sources at 1.6 µm are compact star clusters. With increasing Seyfert type the fraction of unresolved sources detected at 1.6 µm and the ratio of 1.6 µm to [O III] fluxes tend to decrease. These trends are consistent with the unification model for Seyfert 1 and 2 galaxies.