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) withspectropolarimetric observations, we test the suggestion that thepresence of hidden broad-line regions (HBLRs) in Sy2s depends upon theEddington ratio. The stellar velocity dispersion andextinction-corrected [O III] luminosity are used to derive the masses ofcentral supermassive black holes and the Eddington ratio. We find that(1) below an Eddington ratio threshold of 10-1.37, all of theobjects but one are non-HBLR Sy2s, while at higher Eddington ratiosthere is no obvious distinction in the Eddington ratio and black holemass distributions between Sy2s with and without HBLRs; (2) almost nolow-luminosity Sy2s (e.g., L[OIII]<1041 ergss-1) show HBLRs, regardless of the column density of neutralhydrogen; (3) for high luminosities, the possibility of detecting HBLRSy2s is almost the same as that for non-HBLR Sy2s; and (4) whenconsidering only Compton-thin Sy2s with higher [O III] luminosity(>1041 ergs s-1), the detectability of HBLRs isvery high, ~85%. These results suggest that AGN luminosity plays a majorrole in the failure to detect HBLRs in low-luminosity Sy2s, while forhigh-luminosity Sy2s the detectability of HBLRs depends not only uponthe AGN activity, but also upon the torus obscuration.