Binary Black Holes, Gas Sloshing, and Cold Fronts in the X-ray Halo Hosting 4C+37.11

TL;DR

This study uses deep Chandra X-ray observations to analyze the gas dynamics, merger history, and black hole pairing in the galaxy cluster hosting 4C+37.11, revealing evidence of sloshing, cold fronts, and long-lived black hole binaries.

Contribution

First detailed X-ray analysis of the 4C+37.11 cluster revealing gas sloshing, merger history, and long-term black hole binary stability.

Findings

Identified surface brightness jumps indicating gas sloshing.

Estimated the cluster's mass, temperature, and gas fraction.

Inferred the merger occurred 1-2 Gyr ago, with black holes remaining at pc-scale separation for over 2 Gyr.

Abstract

We analyzed deep $Chandra$ ACIS-I exposures of the cluster-scale X-ray halo surrounding the radio source 4C+37.11. This remarkable system hosts the closest resolved pair of super-massive black hole and an exceptionally luminous elliptical galaxy, the likely product of a series of past mergers. We characterize the halo with $r_{500} = 0.95$ Mpc, $M_{500} = (2.5 \pm 0.2) \times 10^{14} \ M_{\rm{\odot}}$, $ kT = 4.6\pm 0.2$ keV, and a gas mass of $M_{\rm g,500} = (2.2 \pm 0.1) \times 10^{13} M_\odot$. The gas mass fraction within $r_{500}$ is $f_{\rm g} = 0.09 \pm 0.01$. The entropy profile shows large non-gravitational heating in the central regions. We see several surface brightness jumps, associated with substantial temperature and density changes, but approximate pressure equilibrium, implying that these are sloshing structures driven by a recent merger. A residual intensity image shows core spiral structure closely matching that seen for the Perseus cluster, although at $z=0.055$ the spiral pattern is less distinct. We infer the most recent merger occurred $1-2$ Gyr ago and that the event that brought the two observed super-massive black holes to the system core is even older. Under that interpretation, this black hole binary pair has, unusually, remained at pc-scale separation for more than 2 Gyr.