A Likely Super Massive Black Hole Revealed by its Einstein Radius in Hubble Frontier Fields Images

TL;DR

This paper demonstrates a novel gravitational lensing method to directly estimate the mass of a supermassive black hole in a distant galaxy, revealing a SMBH of about 8.4 billion solar masses offset from its galaxy center.

Contribution

It introduces a new approach using Einstein radius measurements in Hubble images to directly determine SMBH masses at cosmological distances, independent of luminosity.

Findings

Estimated SMBH mass of approximately 8.4 billion solar masses.

Detected SMBH offset by about 4.4 kpc from galaxy center.

Proposed alternative lensing scenario involving a compact galaxy.

Abstract

At cosmological distances, gravitational lensing can provide a direct measurement of supermassive black hole (SMBH) masses irrespective of their luminosities. Here, we directly estimate the mass of a SMBH in the brightest cluster galaxy (BCG) of MACS J1149+2223.5 at $z=0.54$ through one of the multiply-lensed images of a background spiral galaxy at $z=1.49$ projected close to the BCG. In this particular image, an intrinsically compact region in one of the spiral arms is lensed into an arc that curves towards the BCG center. This arc has a radius of curvature of only $\sim$0."6, betraying the presence of a local compact deflector. Its curvature is most simply reproduced by a point-like object with a mass of $8.4^{+4.3}_{-1.8}\times10^{9}M_\odot$, similar to SMBH masses in local elliptical galaxies having comparable luminosities. The SMBH is noticeably offset by $4.4\pm0.3$ kpc from the BCG light centre, plausibly the result of a kick imparted $\sim2.0\times10^7$ years ago during the merger of two SMBHs, placing it just beyond the stellar core. A similar curvature can be produced by replacing the offset SMBH with a compact galaxy having a mass of $\sim2\times 10^{10}M_\odot$ within a cutoff radius of $<4$ kpc, and an unusually large $M/L>50(M/L)_\odot$ to make it undetectable in the deep Hubble Frontiers Fields image, at or close to the cluster redshift; such a lensing galaxy, however, perturbs the adjacent lensed images in an undesirable way.