AGN jets and a fanciful trio of black holes in the Abell 85 Brightest Cluster Galaxy

TL;DR

This study uses high-resolution radio and X-ray observations to clarify the black hole content in the Abell 85 BCG, showing no evidence for a binary black hole and clarifying the nature of a nearby quasar.

Contribution

It demonstrates how atmospheric seeing effects can mimic binary black holes and clarifies the true nature of a suspected third SMBH in the galaxy.

Findings

No evidence for binary black hole in Abell 85 BCG from radio and X-ray data.

SDSS J004150.75-091824.3 is a background quasar, not associated with the cluster.

High-resolution imaging clarifies black hole content in galaxy cores.

Abstract

A new radio map of the Abell 85 Brightest Cluster Galaxy (BCG) was obtained with the Karl G. Jansky Very Large Array (VLA). With a resolution of 0.02", this radio image shows two kiloparsec-scale bipolar jets emanating from the active galactic nucleus of the Abell 85 BCG. The galaxy core appears as a single entity on the new radio map. It has been assumed that the Abell 85 BCG contained a binary black hole in its core. However, Chandra X-ray data and the new high-resolution radio map show no evidence that the Abell 85 BCG harbors a binary black hole. The assumption that this galaxy contains a binary black hole was based on the analysis of its optical surface brightness profile obtained under poor seeing conditions. We demonstrate how the well-known blurring effects of atmospheric seeing can mimic the effects of a binary supermassive black hole (SMBH). Likewise, SDSS J004150.75-091824.3 was postulated to be "a third" SMBH associated with the BCG. In the optical and X-rays, SDSS J004150.75-091824.3 is a point-like source located ~14" away from the nucleus of the Abell 85 BCG. A new spectrum of SDSS J004150.75-091824.3, obtained with the 10.4-m Gran Telescopio Canarias, reveals that this source is a background quasar at a redshift of z=1.560+/-0.003 and not associated in any way with the Abell 85 cluster.