The unified model of Seyfert galaxies suggests that there are hidden broad-line regions ( HBLRs ) in Seyfert 2 galaxies ( S2s ) .
However , there is increasing 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 S2s with other types of Seyfert galaxies and whether or not they can be included in the unified model .
We assemble two sub-samples consisting of 42 non-HBLR S2s and 44 narrow-line Seyfert 1s ( NLS1s ) with redshift z \leq 0.05 from published literatures to explore this issue .
We compare black hole masses in the galactic centers , accretion rates , infrared color ratio ( f _ { 60 \mu m } / f _ { 25 \mu m } ) as a potential indicator of the dusty torus orientation , [ O iii ] Â \lambda 5007 , radio and far infrared luminosities .
We find that non-HBLR S2s and NLS1s have : 1 ) similar distributions of the black hole masses ( 10 ^ { 6 } -3 \times 10 ^ { 7 } M _ { \odot } ) and the Eddington ratios ( L _ { Bol } / L _ { Edd } \sim 1 ) ; 2 ) significantly different distributions of f _ { 60 \mu m } / f _ { 25 \mu m } ratios ; 3 ) similar distributions of bulge magnitudes and luminosities of [ O iii ] , radio , far infrared emission .
The similarities and differences can be understood naturally if they are intrinsically same but non-HBLR S2s are viewed at larger angles of observer ’ s sight than NLS1s .
We thus suggest that non-HBLR S2s only have ” narrower ” broad line regions and they are the counterparts of NLS1s viewed at high inclination angles .
The absence of the polarized emission line in non-HBLR S2s is caused by the less massive black holes and high accretion rate similar to NLS1s .
The implications of the unification scheme of non-HBLR S2s and NLS1s are discussed .