It is feasible to directly measure black hole masses in the first galaxies

Abstract

In the local universe, black hole masses have been inferred from the observed increase in the velocities of stars at the centres of their host galaxies. So far, masses of supermassive black holes in the early universe have only been inferred indirectly, using relationships calibrated to their locally observed counterparts. Here, we use the latest observational constraints on the evolution of stellar masses in galaxies to predict, for the first time, that the region of influence of a central supermassive black hole at the epochs where the first galaxies were formed is directly resolvable by current and upcoming telescopes. We show that the existence of the black hole can be inferred from observations of the gas or stellar disc out to > 0.5 kpc from the host halo at redshifts z 6. Such measurements will usher in a new era of discoveries unraveling the formation of the first supermassive black holes based on subarcsecond-scale spectroscopy with the JW ST , ALM A, and the SKA. The measured mass distribution of black holes will allow forecasting of the future detection of gravitational waves from the earliest black hole mergers.

A Multi-messenger view of Cosmic Dawn: Conquering the Final Frontier

“…Specifically, since the stellar mass evolves much more modestly than the black hole mass (also found in recent observations, e.g., [195,196]), the dominance of the black hole can be felt at high redshifts to a much greater distance from the centre of the system. This leads to a direct, observable signature [197] of the prevalence of massive black holes in the centres of the first galaxies during the period of reionization. It is found that the influence of the central black hole can dominate the kinematics up to a distance of 0.5 kpc from the centre of the dark matter halo at redshifts z 6.…”