Unveiling Gargantua: A new search strategy for the most massive central cluster black holes

¹ Max Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
² School of Mathematics and Physics, University of Queensland, St. Lucia, QLD 4072, Australia
e-mail: h.baumgardt@uq.edu.au

Received: 1 July 2015
Accepted: 13 September 2015

Abstract

Aims. We aim to unveil the most massive central cluster black holes in the Universe.

Methods. We present a new search strategy, which is based on a black hole mass gain sensitive calorimeter and which links the innermost stellar density profile of a galaxy to the adiabatic growth of its central supermassive black hole (SMBH). As a first step we convert observationally inferred feedback powers into SMBH growth rates using reasonable energy conversion efficiency parameters, ϵ. In the main part of this paper we use these black hole growth rates, sorted in logarithmically increasing steps encompassing our whole parameter space, to conduct N-body computations of brightest cluster galaxies (BCGs) with the newly developed Muesli software. For the initial setup of galaxies, we use core-Sérsic models to account for SMBH scouring.

Results. We find that adiabatically driven core regrowth is significant at the highest accretion rates. As a result, the most massive black holes should be located in BCGs with less pronounced cores when compared to the predictions of empirical scaling relations, which are usually calibrated in less extreme environments. For efficiency parameters ϵ< 0.1, BCGs in the most massive, relaxed, and X-ray luminous galaxy clusters might even develop steeply rising density cusps. Finally, we discuss several promising candidates for follow-up investigations, among them the nuclear black hole in the Phoenix cluster. Based on our results, its central black hole might have a mass of the order of 10¹¹ M_⊙.