Public Seminar of PhD Candidate:- First Direct Mass Measurement of a Distant Supermassive Black Hole through Gravitational Lensing
At cosmological distances, gravitational lensing can in principle provide direct mass measurements of supermassive black holes (SMBH). Here, the speaker present my thesis work on directly estimating 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 towards the BCG centre, 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 ~8.4 x 109 solar masses, similar to SMBH masses in local elliptical galaxies having comparable luminosities. The SMBH is noticeably offset by 4.4 kpc from the BCG light centre, plausibly the result of a kick imparted 2.9 x 107 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 x 1010 solar masses within a cutoff radius of < 4 kpc, and an unusually large M/L > 50 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.