[Paper Review] Evidence for heavy seed origin of early supermassive black holes from a z~10 X-ray quasar

Ákos Bogdán, Andy D. Goulding+10 more|arXiv (Cornell University)|May 24, 2023

Galaxies: Formation, Evolution, Phenomena20 citations

TL;DR

The paper reports the discovery of a heavily obscured, likely Compton-thick accreting black hole with M_BH ~ 10^7–10^8 M_sun at z ~ 10.3 in a JWST-detected lensed galaxy, supporting heavy seed black hole formation.

ABSTRACT

Observations of quasars reveal that many supermassive black holes (BHs) were in place less than 700 million years after the Big Bang. However, the origin of the first BHs remains a mystery. Seeds of the first BHs are postulated to be either light (i.e., $10-100~ m{M_{\odot}})$, remnants of the first stars or heavy (i.e., $10^4-10^5~ m{M_{\odot}})$, originating from the direct collapse of gas clouds. Harnessing recent data from the Chandra X-ray Observatory, we report the detection of an X-ray-luminous massive BH in a gravitationally-lensed galaxy identified by JWST at $z\approx10.3$ behind the cluster lens Abell 2744. This heavily-obscured quasar with a bolometric luminosity of $L_{ m bol}\sim5 imes10^{45}~ m{erg\ s^{-1}}$ harbors a $M_{ m BH}\sim10^7-10^8~ m{M_{\odot}}$ BH assuming accretion at the Eddington limit. This mass is comparable to the inferred stellar mass of its host galaxy, in contrast to what is found in the local Universe wherein the BH mass is $\sim0.1\%$ of the host galaxy's stellar mass. The combination of such a high BH mass and large BH-to-galaxy stellar mass ratio just $\sim$500 Myrs after the Big Bang was theoretically predicted and is consistent with a picture wherein BHs originated from heavy seeds.

Motivation & Objective

• Motivate the origin question of the first black holes and distinguish light vs. heavy seed scenarios.
• Detect and characterize high-redshift accreting black holes using JWST lensing and deep Chandra X-ray data.
• Assess whether the observed black hole mass supports heavy seed formation and Eddington-limited growth.
• Infer implications for black hole-galaxy coevolution at cosmic dawn.

Proposed method

• Combine deep Chandra X-ray observations (1.25 Ms) with JWST-detected lensed galaxies behind Abell 2744 to search for high-z X-ray sources.
• Perform astrometric alignment between Chandra and JWST positions to locate X-ray counterparts.
• Extract X-ray spectra using a small source aperture and an annular background region to isolate the cluster ICM contribution.
• Fit the cluster emission with an APEC model and the source with a MyTorus-based absorbed AGN model to estimate N_H and L_X,int.
• Estimate BH mass from L_X,int with bolometric correction, considering uncertainties in N_H and L_bol/L_X.
• Discuss growth histories of light vs. heavy seeds and compare to the observed UHZ1 properties.

Experimental results

Research questions

• RQ1 Is there X-ray evidence for an accreting black hole in a z~10 JWST-detected lensed galaxy?
• RQ2 Does the inferred black hole mass at z~10.3 favor heavy seed formation over light seeds?
• RQ3 Can the X-ray spectral analysis constrain the column density and intrinsic luminosity of the high-z AGN?
• RQ4 What do the results imply about early black hole growth scenarios and BH-galaxy mass relations?

Key findings

• A statistically significant 4.2 sigma X-ray excess is detected at the position of UHZ1, a z~10.3 galaxy behind Abell 2744.
• Best-fit spectral modeling yields a heavily obscured AGN with N_H ~ 8e24 cm^-2 and L_X,int ~ 9e45 erg/s, though degeneracies with N_H exist.
• After lensing correction (mu = 3.81), the intrinsic 2-10 keV luminosity is constrained to L_X,int ~ 1.9e44 erg/s, implying M_BH ~ 4e7–1e8 M_sun depending on assumptions.
• The inferred BH-to-stellar mass ratio is high for z~10.3, consistent with heavy seed scenarios and OB G evolution, rather than local Universe ratios.
• A light-seed, continuous-Eddington-growth scenario would require implausibly high, sustained super-Eddington accretion and gas supply for hundreds of Myr.
• The results provide direct observational support for heavy seeds as plausible progenitors of early supermassive black holes.