The Eddington Ratios in Seyfert 2 Galaxies with and without Hidden Broad‐Line Regions

Abstract

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 vertical bar O III vertical bar 10(41) ergs s(-1)), the detectability of HBLRs is very high, similar to 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.