The M • ‐σ Relation for Supermassive Black Holes

Abstract

We investigate the differences in the M?-? relation derived recently by Ferrarese & Merritt and by 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 fit 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) ? 108 M?(?c/200 km s-1)4.72(?0.36).