The size of the broad-line regions in dwarf active galaxies

Abstract

Using the empirical relation between black hole mass and bulge velocity dispersion established for active and quiescent galaxies, we derive the sizes of the broad-line regions (BLRs) for 22 dwarf active galaxies. These sizes are compared with those of Seyfert 1 galaxies and quasars. We find that the size of the BLRs of Seyfert 1s and quasars is well scaled with the luminosity of the Hα line with a slope of ≃0.5, and dwarf active galaxies show larger BLRs than the values predicted by the BLR size–luminosity relation for Seyfert 1 galaxies and quasi-stellar objects (QSOs). The results suggest that the BLRs of dwarf active galactic nuclei (AGN) have lower ionization or/and lower density than those of Seyfert 1 galaxies and QSOs. Photoionization calculations show that the large BLRs are consistent with observed emission line spectra.