Black hole masses in narrow-line Seyfert 1 galaxies

The masses of central supermassive black holes in a soft X-ray-selected sample of the narrow-line Seyfert 1 galaxies (NLS1s) are estimated by various methods to test the theoretical models. Apart from the methods using the Hbeta linewidth and the [O III] linewidth, soft X-ray excess as a prominent character of NLS1s is used to estimate the black hole masses. The virial mass derived from the Hbeta linewidth assuming random orbits of broad-line regions (BLRs) is consistent with that from the soft X-ray bump luminosity for NLS1s, 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 NLS1s satisfied by this Eddington limit relation. The masses of these 16 NLS1s derived from X-ray luminosity are systematically larger than that from Hbeta 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 NLS1s is approximately 17degrees, which provided new support for the pole-on orientation effect in NLS1s.