The Brightest Cluster Galaxy in Abell 85: The Largest Core Known so far

TL;DR

This paper reports the discovery of the largest known core in a brightest cluster galaxy, Holm 15A in Abell 85, suggesting it may host an extremely massive black hole and indicating a short evolutionary phase for such large cores.

Contribution

It presents the identification and characterization of the largest core in a BCG, expanding understanding of galaxy core sizes and their relation to supermassive black holes.

Findings

Holm 15A's core radius exceeds 4.5 kpc, the largest known.

Core size suggests potential SMBH mass between 10^9 and 10^11 solar masses.

Large cores may represent a brief evolutionary phase of BCGs.

Abstract

We have found that the brightest cluster galaxy (BCG) in Abell~85, Holm 15A, displays the largest core so far known. Its cusp radius, $r_{\gamma} = 4.57 \pm 0.06$ kpc ($4.26^{\prime\prime}\pm 0.06^{\prime\prime}$), is more than 18 times larger than the mean for BCGs, and $\geq1$ kpc larger than A2261-BCG, hitherto the largest-cored BCG (Postman, Lauer, Donahue, et al. 2012) Holm 15A hosts the luminous amorphous radio source 0039-095B and has the optical signature of a LINER. Scaling laws indicate that this core could host a supermassive black hole (SMBH) of mass $M_{\bullet}\thicksim (10^{9}-10^{11})\,M_{\odot}$. We suggest that cores this large represent a relatively short phase in the evolution of BCGs, whereas the masses of their associated SBMH might be set by initial conditions.