The most massive black holes on the Fundamental Plane of black hole accretion
Abstract
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 L_X ∝ L_R^{0.75 ± 0.08}, favouring 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 per cent) should have BH masses >1010 M⊙ 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.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- February 2018
- DOI:
- 10.1093/mnras/stx2812
- arXiv:
- arXiv:1710.10268
- Bibcode:
- 2018MNRAS.474.1342M
- Keywords:
-
- accretion;
- accretion discs;
- black hole physics;
- galaxies: active;
- galaxies: clusters: general;
- galaxies: jets;
- X-rays: galaxies: clusters;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- Accepted for publication in MNRAS, 22 pages, 12 figures