Correlations Between Supermassive Black Holes, Velocity Dispersions, and Mass Deficits in Elliptical Galaxies with Cores

TL;DR

This paper reveals new correlations between stellar light deficits, black hole masses, and velocity dispersions in elliptical galaxy cores, supporting theories of galaxy formation and black hole influence.

Contribution

It establishes novel correlations linking core light deficits, black hole masses, and velocity dispersions, providing new methods to estimate black hole masses in elliptical galaxies.

Findings

L_def correlates with sigma and MBH

L_def/L ratio correlates with MBH/M

Core ellipticals show distinct properties from extra light ellipticals

Abstract

High-dynamic-range surface photometry in a companion paper makes possible accurate measurement of the stellar light deficits L_def and mass deficits M_def associated with the cores of elliptical galaxies. We show that L_def correlates with the velocity dispersion sigma of the host galaxy bulge averaged outside the central region that may be affected by a supermassive black hole (BH). We confirm that L_def correlates with BH mass MBH. Also, the fractional light deficit L_def/L correlates with MBH/M, the ratio of BH mass to the galaxy stellar mass. All three correlations have scatter similar to or smaller than the scatter in the well known correlation between MBH and sigma. The new correlations are remarkable in view of the dichotomy between ellipticals with cores and those with central extra light. Core light deficit correlates closely with MBH and sigma, but extra light does not. This supports the suggestion that extra light Es are made in wet mergers with starbursts whereas core Es are made in dry mergers. After dry mergers, cores are believed to be scoured by BH binaries that fling stars away as their orbits decay or by BHs that sink back to the center after recoiling from anisotropic gravitational radiation emitted when they merge. Direct evidence has been elusive. We interpret the new correlations as the "smoking gun" that connects cores with BHs. Together, the MBH - sigma and MBH - L_def correlations give us two independent ways to estimate BH masses in core ellipticals.