Dr. Hamsa Padmanabhan

The radiation from the first supermassive black holes (SMBHs) is believed to have played an important role in the reionization of hydrogen and helium in the early universe. I will describe a holistic, multi-messenger approach towards characterizing the properties of these first luminous sources, by combining the immense potential of forthcoming observatories in the gravitational-wave, submillimetre, radio and optical bands. In particular, it is feasible to make a direct, kinematic measurement of the central black hole masses of the very first galaxies (at z ~ 6-10) based on sub-arcsecond scale spectroscopy with the ALMA, GMT/ELT, JWST, VLA and SKA. The gravitational wave (GW) emission from massive black hole binary coalescences is capable of constraining several properties of their host haloes (such as the occupation fractions at high redshift) to sub-percent precision with the forthcoming LISA observatory. Further, it can be shown that robust electromagnetic follow-ups of GW detections of the first SMBHs, coming from the stellar light of the galaxy itself – which is much longer lived than the transient counterparts arising from the gas accretion – are possible using the LSST on the Rubin observatory, enabling a comprehensive study of properties of their hosts.