The M•-σ relation for supermassive black holes

We investigate the differences in the relation derived recently by Ferrarese & Merritt and by M(.)-sigma Gebhardt and collaborators. The shallower slope found by the latter authors (3.75 vs. 4.8) is due partly to the use of a regression algorithm that ignores measurement errors and partly to the value of the velocity dispersion adopted for a single galaxy, the Milky Way. A steeper relation is shown to provide a better Dt to black hole masses derived from reverberation mapping studies. Combining the stellar dynamical, gasdynamical, and reverberation mapping mass estimates, we derive a best-fit relation M(.) = 1.30(+/-0.36) x 10(8) M(.)(sigma (c)/200 km s(-1))(4.72(+/-0.36)).