Black hole masses in narrow-line Seyfert 1 galaxies

Abstract

The masses of central supermassive black holes in a soft X-ray-selected sample of the narrow-line Seyfert 1 galaxies (NLS I s) are estimated by various methods to test the theoretical models. Apart from the methods using the Hβ linewidth and the [O III] linewidth, soft X-ray excess as a prominent character of NLS 1 s is used to estimate the black hole masses. The virial mass derived from the Hβ linewidth assuming random orbits of broad-line regions (BLRs) is consistent with that from the soft X-ray bump luminosity for NLS 1s, but with a larger scatter. The virial black hole masses showed that most of NLS1s are in the super-Eddington accretion state, while most of broad-line Seyfert 1 galaxies are not. We found that the black hole mass estimated from the [O III] linewidth is not in agreement with above two methods. Using the Eddington limit relation for the super-Eddington accretion suggested by Wang, we found that there are 16 NLSIs satisfied by this Eddington limit relation. The masses of these 16 NLS1s derived from X-ray luminosity are systematically larger than that from Hβ linewidth assuming random BLRs orbits. If the mass derived from X-ray luminosity is true, the mean disc inclination to the line of sight in these 16 NLS s is approximately 17°, which provided new support for the pole-on orientation effect in NLS 1 s.