The Eddington ratios in Seyfert 2 galaxies with and without hidden broad-line regions.
BIAN W. and GU Q.
Abstract (from CDS):
Using a large sample of 90 Seyfert 2 galaxies (Sy2s) with spectropolarimetric observations, we test the suggestion that the presence of hidden broad-line regions (HBLRs) in Sy2s depends upon the Eddington ratio. The stellar velocity dispersion and extinction-corrected [O III] luminosity are used to derive the masses of central supermassive black holes and the Eddington ratio. We find that (1) below an Eddington ratio threshold of 10–1.37, all of the objects but one are non-HBLR Sy2s, while at higher Eddington ratios there is no obvious distinction in the Eddington ratio and black hole mass distributions between Sy2s with and without HBLRs; (2) almost no low-luminosity Sy2s (e.g., L[OIII]<1041 ergs/s) show HBLRs, regardless of the column density of neutral hydrogen; (3) for high luminosities, the possibility of detecting HBLR Sy2s is almost the same as that for non-HBLR Sy2s; and (4) when considering only Compton-thin Sy2s with higher [O III] luminosity (>1041 ergs/s), the detectability of HBLRs is very high, ∼85%. These results suggest that AGN luminosity plays a major role in the failure to detect HBLRs in low-luminosity Sy2s, while for high-luminosity Sy2s the detectability of HBLRs depends not only upon the AGN activity, but also upon the torus obscuration.
Galaxies: Active - Galaxies: Seyfert - Polarization