Astronomy Colloquium / Fall 2008

October 8

Prof. Laura Ferrarese

Herzberg Institute of Astrophysics, Victoria, Canada

The Structure of Early-Type Galaxies from the ACS Virgo and Fornax Cluster Surveys: Cores, Stellar Nuclei and Supermassive Black Holes.

In this talk I shall address the connection between global and nuclear structural properties of early-type galaxies, and probe deeper into the SBH-galaxy connection by exploiting the unprecedented view of the inner structure of galactic spheroids afforded by the ACS Virgo and Fornax Cluster Surveys, two large HST programs to image 143 early-type members of the Virgo and Fornax clusters, from giants to dwarfs, spanning a factor of over 700 in B-band luminosity. Particularly revealing is the finding that, in moving from bright to faint early-type galaxies, the surface brightness profiles within the inner few hundred parsecs undergo a systematic but smooth transition from low-density cores to high density stellar nuclei. Cores, which are identified as luminosity deficits relative to the Sersic law best fitting the profiles on kiloparsec scales, are uniquely associated with galaxies brighter than M(B) ~ -20.5 mag, the same galaxies which are believed to hosts SBHs. Stellar nuclei, which are manifested as a luminosity excess over a Sersic fit, are present in as many as 80% of low- and intermediate-luminosity galaxies. Remarkably, SBHs and stellar nuclei obey a similar "M-sigma" relation, and both contain the same mean fraction, ~0.2%, of the total galactic mass. I will argue that the creation of a “central massive object” (CMO) is a generic by-product of galaxy formation, with SBHs and stellar nuclei being the dominant modes of CMO formation in bright and intermediate/faint galaxies respectively.