The Multitude of Unresolved Continuum Sources at 1.6 microns in Hubble Space Telescope images of Seyfert Galaxies

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  • 21 December 1999
Abstract
We examine 112 Seyfert galaxies observed by the Hubble Space Telescope (HST) at 1.6 microns. We find that ~50% of the Seyfert 2.0 galaxies which are part of the Revised Shapeley-Ames (RSA) Catalog or the CfA redshift sample contain unresolved continuum sources at 1.6 microns. All but one of the Seyfert 1.0-1.9 galaxies display unresolved continuum sources. These sources have fluxes of order a mJy, luminosities of order 10^41 ergs/s and absolute magnitudes M_H \~-16. Comparison normal galaxies from the RSA Catalog display significantly fewer (21%), somewhat lower luminosity nuclear sources, which could be due to compact star clusters. We find that the luminosities of the unresolved Seyfert sources at 1.6 microns are correlated with [OIII] 5007A and hard X-ray luminosities, which suggests that the majority of the 1.6 micron sources are non-stellar. We estimate that a few percent of local spiral galaxies contain black holes emitting at moderate fraction, 10^-1 to 10^-4 of their Eddington luminosities. The Seyfert 2.0 galaxies tend to have lower 1.6 micron luminosities compared to Seyfert 1.0-1.9 galaxies with similar [OIII] luminosities, suggesting that there is significant extinction (A_V > 40) towards their continuum emitting region. This offset and the fraction of unresolved sources detected are broadly consistent with the dusty torus unification model for Seyfert 1 and 2 galaxies. Assuming a color typical of a Seyfert 1 galaxy for the non-stellar continuum, only a moderate amount of foreground extinction, A_V > 3, is required to account for the detections of unresolved emission at 1.6 microns and previous non-detections at 0.6 microns.

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