JWST CEERS and JADES Active Galaxies at z = 4-7 Violate the Local M _•-M _⋆ Relation at >3σ: Implications for Low-mass Black Holes and Seeding Models

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 Hα-detected black holes, we investigate (i) the high-z M _•-M _⋆ relation and (ii) the black hole mass distribution, especially in its low-mass range (M _• ≲ 10^6.5 M _⊙). With a detailed statistical analysis, our findings conclusively reveal a high-z M _•-M _⋆ relation that deviates at >3σ confidence level from the local relation. The high-z relation is $\mathrm{log}({M}_{\bullet }/\,{M}_{\odot })=-{2.43}_{-0.83}^{+0.83}+{1.06}_{-0.09}^{+0.09}\mathrm{log}({M}_{\star }/\,{M}_{\odot })$ . Black holes are overmassive by ~10-100× 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× more black holes with M _• ≲ 10^6.5 M _⊙, and 10-30× more with M _• ≲ 10^8.5 M _⊙, compared to local relation's predictions. The lighter black holes preferentially occupy galaxies with a stellar mass of ~10^7.5-10⁸ M _⊙. We have yet to detect these sources because (i) they may be inactive (duty cycles 1%-10%), (ii) the host overshines the active galactic nucleus (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 _•-M _⋆ 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 coevolution with their galactic hosts.