On the Black Hole Mass - Bulge Mass Relation

We have re-examined the relation between the mass of the central black holes in nearby galaxies, M_bh, and the stellar mass of the surrounding spheroid or bulge, M_bulge. For a total of 30 galaxies bulge masses were derived through Jeans equation modeling or adopted from dynamical models in the literature. In stellar mass-to-light ratios the spheroids and bulges span a range of a factor of eight. The bulge masses were related to well-determined black hole masses taken from the literature. With these improved values for M_bh, compared to Magorrian et al. (1998), and our redetermination of M_bulge, we find the M_bh-M_bulge relation becomes very tight. We find M_bh ~ M_bulge^(1.12+/-0.06) with an observed scatter of < 0.30 dex, a fraction of which can be attributed to measurement errors. The scatter in this relation is therefore comparable to the scatter in the relations of M_bh with sigma and the stellar concentration. These results confirm and refine the work of Marconi and Hunt (2003). For M_bulge~5x10^10 M_sun the median black hole mass is 0.14% +/- 0.04% of the bulge mass.