THE DIFFERENT NATURE OF SEYFERT 2 GALAXIES WITH AND WITHOUT HIDDEN BROAD-LINE REGIONS

We compile a large sample of 120 Seyfert 2 galaxies (Sy2s) which contains 49 hidden broad-line region (HBLR) Sy2s and 71 non-HBLR Sy2s. From the difference in the power sources between two groups, we test whether HBLR Sy2s are dominated by active galactic nuclei (AGNs) and whether non-HBLR Sy2s are dominated by starbursts. We show that (1) HBLR Sy2s have larger accretion rates than non-HBLR Sy2s; (2) HBLR Sy2s have larger [ Ne v] lambda 14.32/[Ne II] lambda 12.81 and [O IV] lambda 25.89/[ Ne II] lambda 12.81 line ratios than non-HBLR Sy2s; and (3) HBLR Sy2s have smaller IRAS f(60)/f(25) flux ratios, which show the relative strength of the host galaxy and nuclear emission, than non-HBLR Sy2s. Consequently, we suggest that HBLR Sy2s and non-HBLR Sy2s are AGN dominated and starburst dominated, respectively. In addition, non-HBLR Sy2s can be classified into luminous (L-[O III] > 10(41) erg s(-1)) and less luminous (L-[O III] < 10(41) erg s(-1)) samples, when considering only their obscuration. We suggest that (1) the invisibility of polarized broad lines (PBLs) in the luminous non-HBLR Sy2s depends on the obscuration and (2) the invisibility of PBLs in the less luminous non-HBLR Sy2s depends on the very low Eddington ratio rather than the obscuration.