Radiation pressure force and black hole mass determination in low redshift type-I and type-II active galactic nuclei

Abstract

The distributions of L(oiii 5007), black hole (BH) mass and L/L(Edd) in two large samples of type-I and type-II active galactic nuclei (AGNs) are compared in order to test the suggestion that radiation pressure force is affecting the gas velocity in the broad line region and hence the BH mass determination. The samples are drawn from the SDSS archive and are modified to represent the same parent distribution at 0.1 < z < 0.2. BH masses in type-I sources are calculated in two different ways, one using a simple virial mass assumption and the other by taking into account the effect of radiation pressure force on the gas. The simple virial mass estimate results in good agreement with the sigma*-based BH mass and L/L(Edd) estimates in type-II sources. In contrast, there is a clear disagreement in the L/L(Edd) distributions when radiation pressure-based estimates are used. This indicates that radiation pressure force is not important in 0.1 < z < 0.2 AGNs with L(5100)=10^{42.8-44.8} erg/s. This has important implications to the physics of the gas producing the broad emission lines in AGNs, in particular the existence of extremely large (about 10^24 cm^(-2)) column density clouds.