A Search for the Most Massive Galaxies. III. Global and Central Structure

TL;DR

This study uses high-resolution Hubble images to analyze the core structures of massive galaxies, revealing correlations between luminosity, core size, and black hole mass, and highlighting differences between core and power-law galaxies.

Contribution

It provides detailed measurements of galaxy core properties in the most massive galaxies, linking core size and mass deficits to black hole mass estimates and galaxy luminosity.

Findings

Core sizes correlate more strongly with luminosity than velocity dispersion.

Mass deficits are roughly twice the black hole masses from the M_bh-sigma relation.

Power-law galaxies show steeper inner profiles and higher ellipticity.

Abstract

We used the Advanced Camera for Surveys on board the Hubble Space Telescope to obtain high resolution i-band images of the centers of 23 single galaxies, which were selected because they have SDSS velocity dispersions larger than 350 km/s. The surface brightness profiles of the most luminous of these objects (M_i<-24) have well-resolved `cores' on scales of 150-1000 pc, and share similar properties to BCGs. The total luminosity of the galaxy is a better predictor of the core size than is the velocity dispersion. The correlations of luminosity and velocity dispersion with core size agree with those seen in previous studies of galaxy cores. Because of high velocity dispersions, our sample of galaxies can be expected to harbor the most massive black holes, and thus have large cores with large amounts of mass ejection. The mass-deficits inferred from core-Sersic fits to the surface-brightness profiles are approximately double the black-hole masses inferred from the M_bh-sigma relation and the same as those inferred from the M_bh-L relation. The less luminous galaxies (M_i>-23) tend to have steeper `power-law' inner profiles, higher-ellipticity, diskier isophotes, and bulge-to-total ratios of order 0.5 -- all of which suggest that they are `fast-rotators' and rotational motions could have contaminated the velocity dispersion estimate. There are obvious dust features within about 300 pc of the center in about 35% of the sample, predominantly in power-law rather than core galaxies.