Supermassive black holes in brightest cluster galaxies

We want to characterize the high mass end of the local supermassive black hole (SMBH) mass function. Indeed, it is in the high mass regime that the unavoidable link between the evolution of SMBHs and the hierarchical build-up of galaxies leaves its clearest signature. We carefully selected three brightest cluster galaxies (BCG). Their large masses, luminosities and stellar velocity dispersions, as well as their having a merging history which is unmatched by galaxies in less crowded environments, make these galaxies the most promising hosts of the most massive SMBHs in the local Universe. We observed the BCG sample with the Space Telescope Imaging Spectrograph (STIS) and the Advanced Camera for Surveys (ACS). For each target galaxy we performed high-resolution spectroscopy of the H-alpha + [NII] emission lines at three slit positions, to measure the central ionized gas kinematics. Two galaxies, named Abell 3565-BCG and Abell 1836-BCG, show a regular rotation curve and a strong central velocity gradient. ACS images with three filters (F435W, F625W and FR656N) have been used to determine the optical depth of the dust, the stellar mass distribution near the nucleus and an intensity map. We used a dynamical model of the gaseous disk taking into account the whole bi-dimensional velocity field and the instrumental set-up. The extension of the high mass end of the local SMBH mass unction is necessary to improve our understanding of how SMBHs, and their hosts, formed and evolved.