The Nature of Accretion in Seyfert Galaxies

Abstract

We present statistical results from a sample of 91,006 Seyfert galaxies obtained from SDSS DR14 (Sloan Digital Sky Survey Data Release 14). Using the ratio of the flux of doubly ionized oxygen [OIII] to that of the flux of hydrogen beta line Hβ, the Seyfert galaxy sample was separated into Seyferts 1 and 2. For each class of Seyfert galaxy, both bolometric luminosity and Eddington luminosity were calculated and these results were used to investigate the nature of accretion in both classes by estimating their Eddington ratios. The susceptibility of the [OIII] line to reddening necessitated its being extinction corrected before calculating bolometric luminosity from Lbol=3500L[OIII]. Our work shows that Seyfert 2 galaxies are 10 times more luminous than their Seyfert 1 counterparts. We also found Seyfert 2 galaxies to be centrally more massive than Seyfert 1 galaxies as a result of which Eddington ratio is less in Seyfert 1 galaxies. These results show that both Seyferts 1and 2 galaxies are powered by thick accretion disk and as such undergo predominantly super-Eddington accretion. Only a negligible percent of them (0.49% for Seyfert 1 galaxies and 0.28% for Seyfert 2 galaxies) are powered by thin accretion disk. Our results also indicate that black hole growth in both Seyfert 1 and Seyfert 2 galaxies is dominated by super-Eddington accretion rather than sub-Eddington accretion showing that though both Seyfert classes are good accretors, Seyfert 2 galaxies are better accretors and this means that Seyferts of thin accretion disks are still in the low-Eddington accretion era.