Massive black holes in Galactic Nuclei

Key:

Triangle - kinematics of gas

Circle - dynamics of stars

Diamond - masers

Square - Ground-based stellar kinematics

There is growing evidence that many, if not most, galaxies contain massive black holes at their centers. There are enough observations to make estimates of the number of massive black holes based on the masses of galaxies.

The figure shows the mass estimates of the candidate massive black holes in galaxies plotted against the bulge luminosity of their host galaxy. The labeled points are the results of painstaking observation and detailed modeling. The symbols indicate how the mass estimate was derived. Arrows indicate upper limits on the black hole mass. The solid line is a model with M_bh = 0.005 M_bulge and M_bulge = 5 [L_bulge/10⁹L_☉] ^1.2. The distribution of M_bh is roughly Gaussian in log (M_bh/M_bulge). The dashed line is the quasar light prediction apportioned according to bulge mass:

M_bh = 2 x 10⁷[L_bulge/(5 x 10⁹L_☉)]^1.2

The small offset from the observed black-hole/bulge-mass relation indicates that the present integrated density in massive black holes is broadly consistent with the integrated luminosity produced by active galactic nuclei over the life of the Universe. This offset may reflect a radiative efficiency of average quasar accretion less than 0.10.

Ref:D. Richstone et al. Nature 395, A14 1998