Detection of faint broad emission lines in type 2 AGN - II. On the measurement of the black hole mass of type 2 AGN and the unified model

Abstract

We report the virial measurements of the black hole (BH) mass of a sample of 17 type 2 active galactic nuclei (AGN), drawn from the Swift/BAT 70-month 14-195 keV hard X-ray catalogue, where a faint BLR component has been measured via deep NIR (0.8-2.5 μm) spectroscopy. We compared the type 2 AGN with a control sample of 33 type 1 AGN. We find that the type 2 AGN BH masses span the 5 < log(M<SUB>BH</SUB>/M<SUB>☉</SUB>) < 7.5 range, with an average log(M<SUB>BH</SUB>/M<SUB>☉</SUB>) = 6.7, which is ∼0.8 dex smaller than found for type 1 AGN. If type 1 and type 2 AGN of the same X-ray luminosity log(L_{14-195}/erg s<SUP>-1</SUP>) ∼ 43.5 are compared, type 2 AGN have 0.5 dex smaller BH masses than type 1 AGN. Although based on few tens of objects, this result disagrees with the standard AGN unification scenarios in which type 1 and type 2 AGN are the same objects observed along different viewing angles with respect to a toroidal absorbing material.