The Unified Model of Active Galactic Nuclei. II. Evolutionary Connection

(Abbreviated) We assemble a sample composed of 243 nearby Seyfert galaxieswith redshifts $z\le 0.05$ to test the unification scheme. The sample contains94 BLS1s, 44 NLS1s, 36 X-ray absorbed HBLR S2s, 42 X-ray absorbed non-HBLR S2sand 27 X-ray unabsorbed Seyfert 2s (unabsorbed non-HBLR S2s and HBLR S2s). Wefind that: 1) NLS1s have less massive black hole masses than BLS1s; 2) HBLRS2shave the same mass distribution of the black holes with BLS1s; 3) the absorbednon-HBLR S2s have less massive black holes than HBLR S2s; 4) unabsorbednon-HBLR S2s have the most massive black holes. We thus have a queue of blackhole masses from small to large: narrow to broad line Seyfert galaxies,providing new evidence for the evolutionary sequence of Seyfert galaxies. Wefind that the opening angles of the torus in NLS1s and absorbed non-HBLR S2sare significantly smaller than that in BLS1s and HBLR S2s. The growth of theblack holes and increases of the opening angles of the tori determine thevarious appearances of Seyfert galaxies. We also find that the unabsorbedSeyfert 2 galaxies could be caused by low gas-to-dust ratios in the presentsample. This indicates that the star formation histories could be different inthe unabsorbed from in absorbed Seyfert 2 galaxies, showing evidence forsuppressed star formation by black hole activities. We outline a newunification scheme based on the orientation hypothesis: Seyfert galaxies can beunified by including growth of black holes, Eddington ratios, changing openingangles of tori and gas-to-dust ratios in the tori. Seyfert galaxies are tendingto finally evolve to unabsorbed non-HBLR Seyfert 2 galaxies, in which the blackholes are accreting with low accretion rates and both the broad line region anddusty torus disappear.Comment: ApJ, vol 661 (2007), in pres