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 (NLS1s) are estimated by some different methods to test their theoretical models. Apart from the methods using the H$\beta$ 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 H$\beta$ linewidth assuming random orbits of broad-line reigns (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 (BLS1s) are not. We found that the black hole mass estimated from [O III] linewidth is not in agreement with above two methods. Using the Eddington limit relation for the super-Eddington accretion suggested by Wang (2004), we found that there are 16 NLS1s satisfied with this Eddington limit relation. The masses of these 16 NLS1s derived from X-ray luminosity are systematically larger than that from H$\beta$ linewidth assuming random BLRs orbits. If the mass derived from X-ray luminosity is true, the mean disk inclination to the line of sight in these 16 NLS1s is about $17^{\circ}$, which provided new support for the pole-on orientation effect in NLS1s.