The M_BH-σ* relation in local active galaxies

We examine whether active galaxies obey the same relation between black hole mass and stellar velocity dispersion as inactive systems, using the largest published sample of velocity dispersions for active nuclei to date. The combination of 56 original measurements with objects from the literature not only increases the sample from the 15 considered previously to 88 objects but allows us to cover an unprecedented range in both stellar velocity dispersion (30-268 km s^-1) and black hole mass (10⁵-10^8.6 M_⊙). In the M/_BH-σ*. relation of active galaxies, we find a lower zero point than the best-fit relation of Tremaine et al. for inactive galaxies, and an upper limit on the intrinsic scatter of 0.4 dex. There is also evidence of a flatter slope at low black hole masses. We discuss potential contributors to the observed offsets, including variations in the geometry of the broad-line region, evolution in the M_BH- σ* relation, and differential growth between black holes and galaxy bulges.