Theoretical astrophysics and plasma physics at RPC

Abstract:

We describe a correlation between the mass Mbh of a galaxy's central black hole and the luminosity-weighted line-of-sight velocity dispersion σe within the half-light radius. The result is based on a sample of 26 galaxies, including 13 galaxies with new determinations of black hole masses from Hubble Space Telescope measurements of stellar kinematics. The best-fit correlation is Mbh = 1.2(±0.2) × 10⁸ M⊙(σe/200 km s^-1)^{3.75 (±0.3)}over almost 3 orders of magnitude in Mbh; the scatter in Mbh at fixed σe is only 0.30 dex, and most of this is due to observational errors. The Mbh-σe relation is of interest not only for its strong predictive power but also because it implies that central black hole mass is constrained by and closely related to properties of the host galaxy's bulge.

Abstract:

We generalize to elliptical models an argument introduced by Gould, which connects the microlensing optical depth toward the Galactic bulge to the Galactic rotation curve. When applied to the latest value from the MACHO collaboration for the optical depth for microlensing of bulge sources, the argument implies that even a barred Galactic model cannot plausibly reconcile the measured values of the optical depth, the rotation curve, and the local mass density. Either there is a problem with the interpretation of the microlensing data or our line of sight to the Galactic center is highly atypical in that it passes through a massive structure with small solid angle as seen from the Galactic center.