2017/10/31 by M. Mezcua, J. Hlavacek-Larrondo, J. R. Lucey +3 · 1 citation
Physics and Astronomy · #astro-ph.GA
paper · pdf · doi:10.1093/mnras/stx2812
Accepted for publication in MNRAS, 22 pages, 12 figures
arxiv created 2017/11/06 · arxiv updated 2017/11/08
We perform a detailed study of the location of brightest cluster galaxies (BCGs) on the fundamental plane of black hole (BH) accretion, which is an empirical correlation between a BH X-ray and radio luminosity and mass supported by theoretical models of accretion. The sample comprises 72 BCGs out to z∼0.3 and with reliable nuclear X-ray and radio luminosities. These are found to correlate as LX ∝ LR0.75 ± 0.08, favoring an advection-dominated accretion flow as the origin of the X-ray emission. BCGs are found to be on average offset from the fundamental plane such that their BH masses seem to be underestimated by the MBH-MK relation a factor ∼10. The offset is not explained by jet synchrotron cooling and is independent of emission process or amount of cluster gas cooling. Those core-dominated BCGs are found to be more significantly offset than those with weak core radio emission. For BCGs to on average follow the fundamental plane, a large fraction (∼40%) should have BH masses > 1010 M\odot and thus host ultramassive BHs. The local BH-galaxy scaling relations would not hold for these extreme objects. The possible explanations for their formation, either via a two-phase process (the BH formed first, the galaxy grows later) or as descendants of high-z seed BHs, challenge the current paradigm of a synchronized galaxy-BH growth.