JWST CEERS & JADES Active Galaxies at z = 4-7 Violate the Local $M_\bullet-M_\star$ Relation at $>3σ$: Implications for Low-Mass Black Holes and Seeding Models (2308.12331v2)

Abstract: JWST is revolutionizing our understanding of the high-$z$ Universe by expanding the black hole horizon, looking farther and to smaller masses, and revealing the stellar light of their hosts. By examining JWST galaxies at $z=4-7$ that host H$\alpha$-detected black holes, we investigate (i) the high-$z$ $M_\bullet-M_\star$ relation and (ii) the black hole mass distribution, especially in its low-mass range ($M_\bullet \lesssim 10^{6.5} M_\odot$). With a detailed statistical analysis, our findings conclusively reveal a high-$z$ $M_\bullet-M_\star$ relation that deviates at $>3\sigma$ confidence level from the local relation. The high-$z$ relation is: $\log(M_\bullet/M_\odot) = -2.43^{+0.83}_{-0.83} + 1.06^{+0.09}_{-0.09} \log(M_\star/M_\odot)$. Black holes are overmassive by $\sim 10-100\times$ compared to their low-$z$ counterparts in galactic hosts of the same stellar mass. This fact is not due to a selection effect in surveys. Moreover, our analysis predicts the possibility of detecting in high-$z$ JWST surveys $5-15\times$ more black holes with $M_\bullet \lesssim 10^{6.5} M_\odot$, and $10-30\times$ more with $M_\bullet \lesssim 10^{8.5} M_\odot$, compared to local relation's predictions. The lighter black holes preferentially occupy galaxies with a stellar mass of $\sim 10^{7.5}-10^8 M_\odot$. We have yet to detect these sources because (i) they may be inactive (duty cycles $1\%-10\%$), (ii) the host overshines the AGN, or (iii) the AGN is obscured and not immediately recognizable by line diagnostics. A search of low-mass black holes in existing JWST surveys will further test the $M_\bullet-M_\star$ relation. Current JWST fields represent a treasure trove of black hole systems at $z = 4-7$; their detection will provide crucial insights into their early evolution and co-evolution with their galactic hosts.

• The paper reveals that high-redshift galaxies host black holes 10–100× overmassive relative to their stellar mass, deviating from local scaling at >3σ significance.
• It uses JWST’s CEERS and JADES observations combined with MCMC analysis to control for biases and establish a steeper, more scattered M•–M☆ relation.
• The findings challenge standard black hole seeding models and propose a revised view on the co-evolution of early galaxies and supermassive black holes.

Analysis of High-Redshift Active Galaxies: Implications from JWST Observations

The paper "JWST CEERS and JADES Active Galaxies at $z = 4-7$ Violate the Local $M_\bullet-M_\star$ Relation at $>3\sigma$: Implications for Low-Mass Black Holes and Seeding Models" explores the properties of supermassive black holes (SMBHs) and their host galaxies at high redshifts using observations from the James Webb Space Telescope (JWST). The work focuses primarily on the $M_\bullet-M_\star$ scaling relation at redshifts $z = 4-7$, questioning an extrapolation of local relations to these earlier cosmic epochs.

Key Findings and Methodology

This paper leverages JWST's data from the CEERS and JADES fields to investigate the scaling relation between the mass of SMBHs ($M_\bullet$) and the stellar mass ($M_\star$) of their host galaxies. Central to the paper is the departure of observed high-redshift systems from the local $M_\bullet-M_\star$ relation defined by \cite{Reines_Volonteri_2015}, with deviations observed at a $>3\sigma$ confidence level. Through a meticulous statistical analysis using a Markov Chain Monte Carlo (MCMC) approach, the authors establish a new high-redshift $M_\bullet-M_\star$ relation, proposing a steeper slope and larger scatter compared to the local universe.

Their findings suggest that black holes at these redshifts are overmassive by approximately $10-100$ times relative to their local counterparts of similar stellar mass hosts. This deviation arises not from selection effects but indicates a different growth history or initial seeding conditions for these early cosmic structures.

Statistical and Observational Framework

The paper employs a robust analytical framework to derive its conclusions. The authors account for potential observational biases, such as the flux limit sensitivities of JWST's NIRSpec instrument, and adjust for these within their models. By fitting the data within the context of the galaxy stellar mass function, the paper effectively assesses the likelihood of observing specific black hole masses at given stellar masses.

The authors also address systematic uncertainties in estimating black hole and stellar masses, concluding that these are insufficient to account for the magnitude of the observed departures from local relations.

Implications and Future Directions

The implications of these findings are multifaceted. The apparent overmassiveness of high-redshift black holes relative to their stellar hosts challenges existing theories of black hole and galaxy co-evolution, particularly questioning the universality of the local $M_\bullet-M_\star$ relation.

This research prompts a reconsideration of black hole seed models. The early Universe, as portrayed by JWST observations, suggests possible scenarios of black hole seeds growing at a faster rate than their stellar counterparts, or alternatively, that initial seed masses were much larger than those modeled in current light seed paradigms.

Furthermore, the paper speculates on the detectability of low-mass black holes ($M_\bullet \lesssim 10^{6.5} M_\odot$) in extant JWST fields, which could provide critical insights for understanding the early mass distribution of black holes. The results suggest that such low-mass black holes should be observable in current surveys at rates significantly higher than observed, potentially accessible with further deep field observations or alternative detection strategies.

Conclusion

This paper presents a comprehensive paper into the nature of early SMBHs, providing a crucial piece to the puzzle of cosmic evolution. By pushing the observational frontier, JWST not only enhances our ability to detect faint black holes at higher redshifts but also challenges the assumptions of black hole and galaxy co-evolution models. Continued refinement of these models is essential, alongside future observations that probe both the low and high-mass ends of the SMBH spectrum, to unravel the intricacies of their formation and growth in the early Universe.