First Detection of an Over-Massive Black Hole Galaxy UHZ1: Evidence for Heavy Black Hole Seed Formation from Direct Collapse (2308.02654v3)

Abstract: The recent Chandra-JWST discovery of a quasar in the z = 10.1 galaxy UHZ1 reveals that accreting supermassive black holes (SMBHs) were already in place 470 million years after the Big Bang. The Chandra X-ray source detected in UHZ1 is a Compton-thick quasar with a bolometric luminosity of $L_{\rm bol}\sim5\times10^{45}\ \rm{erg\ s^{-1}},$ which corresponds to an estimated BH mass of $\sim4\times10^7 \ \rm{M_{\odot}}$ assuming accretion at the Eddington rate. JWST NIRCAM and NIRSpec data yield a stellar mass estimate for UHZ1 comparable to its BH mass. These characteristics are in excellent agreement with prior theoretical predictions for a unique class of transient, high-redshift objects, Over-massive Black Hole Galaxies [OBGs] by Natarajan et al. that harbor a heavy initial black hole seed that likely formed from the direct collapse of the gas. Based on the excellent agreement between the observed multi-wavelength properties of UHZ1 with theoretical model template predictions, suggests that UHZ1 is the first detected OBG candidate. Our assertion rests on multiple lines of concordant evidence between model predictions and the following observed properties of UHZ1: its X-ray detection and the estimated ratio of the X-ray flux to the IR flux that is consistent with theoretical expectations for a heavy initial BH seed; its high measured redshift of z = 10.1, as predicted for the transient OBG stage (9 < z< 12); the amplitude and shape of the detected JWST Spectral Energy Distribution (SED) between 1 - 5 microns, which is in very good agreement with simulated template SEDs for OBGs; and the extended JWST morphology of UHZ1 that is suggestive of a recent merger, also expected for the formation of transient OBGs. As the first OBG candidate, UHZ1 provides compelling evidence for the formation of heavy initial seeds from direct collapse in the early Universe.

• The paper identifies UHZ1 as an over-massive black hole galaxy at z≈10.1, revealing a central SMBH nearly equal in mass to its stellar component.
• The methodology combines Chandra X-ray and JWST infrared observations, aligning with predictions for heavy black hole seed formation via direct collapse.
• The study’s key implication is that early universe galaxies can host SMBHs formed through direct gas collapse, challenging conventional growth models.

First Detection of an Over-Massive Black Hole Galaxy UHZ1: An Analysis

This paper provides a detailed exposition of the discovery of the over-massive black hole galaxy UHZ1, situated at a redshift of approximately 10.1. The detection was facilitated by the combined observations from the Chandra X-ray Observatory and the James Webb Space Telescope (JWST). The authors reveal that UHZ1 harbors a supermassive black hole (SMBH) with a mass estimate of approximately $4 \times 10^7$ solar masses, accompanied by a comparable stellar mass. The X-ray source in UHZ1 is characterized as a Compton-thick quasar, indicating significant absorption of its soft X-rays by surrounding gas.

This discovery substantiates the theoretical predictions surrounding over-massive black hole galaxies (OBGs), a novel class of high-redshift objects posited to emerge from the direct collapse of gas leading to the formation of heavy initial black hole seeds. These theories, particularly those articulated by Natarajan et al., predict scenarios where the forming SMBHs are almost comparable in mass to their host stellar systems, significantly deviating from the local universe's black hole-to-stellar mass relationship, where the central black hole typically comprises about 0.1% of the stellar mass.

Key Observational Data and Theoretical Alignment

The observational properties of UHZ1 align well with theoretical models postulated for OBGs:

1. Photometry and Redshift: The galaxy's high redshift ($z \approx 10.1$) falls within the predicted range for this transitory OBG phase, which theoretical models project to occur between $9 < z < 12$.
2. Spectral Energy Distribution (SED): The JWST-detected SED between 1 and 5 microns resonates closely with the simulated templates for OBGs. This suggests that the multimodal data observed in UHZ1 fits within the theoretical framework providing a coherent picture of its astrophysical characteristics.
3. X-ray and Infrared Flux Ratio: The X-ray luminosity and the calculated ratio of X-ray to infrared flux corroborate the theoretical expectations for a heavy initial black hole seed, distinguishing UHZ1 from other high-redshift galaxies harboring lighter seeds.
4. Morphological Evidence: The spatially extended morphology captured by JWST implies a recent galactic merger, a condition consistent with the formation narratives postulated for OBGs during their transitional evolutionary phase.

Implications and Future Prospects

The detection of UHZ1 offers compelling evidence supporting heavy black hole seed formation via direct collapse as an early universe phenomenon. This discovery challenges previous assumptions that such mass accumulations could only ensue from lighter ancestral stars. The implications extend toward understanding accretion behaviors and the interplay between nascent galaxies and their central black holes.

Theoretically, this could recalibrate the models estimating the growth timelines of black holes, particularly at high redshift epochs. Practically, it prompts reevaluations of observational strategies focusing on deep-field surveys using next-generation telescopes and advanced multi-wavelength techniques.

Future developments in cosmological simulations are expected to incorporate these empirical benchmarks, aiming for more accurate portrayals of the universe's early SMBH formation phases. Moreover, ongoing campaigns with instruments like JWST hold the potential to uncover further OBGs, significantly enriching understanding and constraining models centered on initial BH seed formation and growth mechanisms in the nascent universe. Overall, UHZ1 sets a foundational precedent, paving the way for elucidating fundamental astrophysical processes in the universe's formative epochs.