A candidate supermassive black hole in a gravitationally-lensed galaxy at $z\approx10$

TL;DR

This paper reports the detection of a candidate supermassive black hole at redshift 10, supporting the heavy seed formation scenario, and constructs the first AGN luminosity function at this epoch, indicating a higher-than-expected black hole abundance.

Contribution

It presents the first evidence of a supermassive black hole at z≈10 and constructs the earliest AGN luminosity function, providing new insights into black hole seed formation.

Findings

Detection of a candidate black hole with ~8×10^7 M☉ at z≈10

Construction of the first AGN luminosity function at z≈10

Indication of a higher-than-expected black hole formation efficiency

Abstract

While supermassive black holes (BHs) are widely observed in the nearby and distant universe, their origin remains debated with two viable formation scenarios with light and heavy seeds. In the light seeding model, the first BHs form from the collapse of massive stars with masses of $10-100 \ \rm{M_{\odot}}$, while the heavy seeding model posits the formation of $10^{4-5} \ \rm{M_{\odot}}$ seeds from direct collapse. The detection of BHs at redshifts $z\gtrsim10$, edging closer to their formation epoch, provides critical observational discrimination between these scenarios. Here, we focus on the JWST-detected galaxy, GHZ 9, at $z\approx10$ that is lensed by the foreground cluster, Abell 2744. Based on 2.1 Ms deep Chandra observations, we detect a candidate X-ray AGN, which is spatially coincident with the high-redshift galaxy, GHZ 9. The BH candidate is inferred to have a bolometric luminosity of $(1.0^{+0.5}_{-0.4})\times10^{46} \ \rm{erg \ s^{-1}}$, which corresponds to a BH mass of $(8.0^{+3.7}_{-3.2})\times10^7 \ \rm{M_{\odot}}$ assuming Eddington-limited accretion. This extreme mass at such an early cosmic epoch suggests the heavy seed origin for this BH candidate. Based on the Chandra and JWST discoveries of extremely high-redshift quasars, we have constructed the first simple AGN luminosity function extending to $z\approx10$. Comparison of this luminosity function with theoretical models indicates an over-abundant $z\approx10$ BH population, consistent with a higher-than-expected seed formation efficiency.