The Unified Model of Active Galactic Nuclei. I. Non–Hidden Broad‐Line Region Seyfert 2 and Narrow‐Line Seyfert 1 Galaxies

The unified model of Seyfert galaxies suggests that there are hiddenbroad-line regions (HBLRs) in Seyfert 2 galaxies (S2s). However, there isincreasing evidence for the appearance of a subclass of S2s lacking of HBLR(non-HBLR S2s). An interesting issue arises as to relations of non-HBLR S2swith other types of Seyfert galaxies and whether or not they can be included inthe unified model. We assemble two sub-samples consisting of 42 non-HBLR S2sand 44 narrow-line Seyfert 1s (NLS1s) with redshift $z\le 0.05$ from publishedliteratures to explore this issue. We compare black hole masses in the galacticcenters, accretion rates, infrared color ratio ($f_{60 \mu \rm m}/f_{25 \mu \rmm}$) as a potential indicator of the dusty torus orientation, \oiii $\lambda5007$, radio and far infrared luminosities. We find that non-HBLR S2s and NLS1shave: 1) similar distributions of the black hole masses ($10^6-3\times10^7\sunm$) and the Eddington ratios ($L_{\rm Bol}/L_{\rm Edd}\sim 1$); 2)significantly different distributions of $f_{60 \mu \rm m}/f_{25 \mu \rm m}$ratios; 3) similar distributions of bulge magnitudes and luminosities of [O{\sc iii}], radio, far infrared emission. The similarities and differences canbe understood naturally if they are intrinsically same but non-HBLR S2s areviewed at larger angles of observer's sight than NLS1s. We thus suggest thatnon-HBLR S2s only have "narrower" broad line regions and they are thecounterparts of NLS1s viewed at high inclination angles. The absence of thepolarized emission line in non-HBLR S2s is caused by the less massive blackholes and high accretion rate similar to NLS1s. The implications of theunification scheme of non-HBLR S2s and NLS1s are discussed.Comment: 13 page in emulateapj.sty, ApJ in pres