A likely supermassive black hole revealed by Its Einstein radius in Hubble frontier fields images

Abstract

At cosmological distances, gravitational lensing can in principle provide direct mass measurements of supermassive black holes (SMBHs). Here, we directly estimate the mass of a SMBH in the brightest cluster galaxy (BCG) of MACS J1149.5+2223 at z = 0.54 using one of the multiply lensed images of a background spiral galaxy at z = 1.49 projected close to the BCG. A lensed arc is curved toward the BCG center, corresponding to an intrinsically compact region in one of the spiral arms. This arc has a radius of curvature of only ∼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 , similar to SMBH masses in local elliptical galaxies having comparable luminosities. The SMBH is noticeably offset by 4.4 ± 0.3 kpc from the BCG light center, which is plausibly the result of a kick imparted ∼2.0 ×10 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 ∼2 ×10 M within a cutoff radius of <4 kpc, and an unusually large to make it undetectable in the deep Hubble Frontiers Fields image, at or close to the cluster redshift. However, such a lensing galaxy perturbs the adjacent lensed images in an undesirable way.© 2018. The American Astronomical Society. All rights reserved..The authors would like to thank the anonymous referee for providing detailed and constructive suggestions to improve this paper. J.L. acknowledges support from the Research Grants Council of Hong Kong through grant 17319316. J.L. also acknowledges a Seed Fund for Basic Research from the University of Hong Kong. T.B. was supported by a Visiting Research Professor Scheme from the University of Hong Kong, during which major parts of this work were conducted. J.M.D. acknowledges the support of projects AYA2015-64508-P (MINECO/FEDER, UE), AYA2012-39475-C02-01, and the consolider project CSD2010-00064 funded by the Ministerio de Economia y Competitividad. Y.O. is supported by the Ministry of Science and Technology (MOST) of Taiwan, MOST 106-2112-M001-008