JADES. The diverse population of infant Black Holes at 4<z<11: merging, tiny, poor, but mighty

TL;DR

This study uncovers a diverse population of early black holes at redshifts 4 to 11, revealing their properties, growth rates, and potential role in cosmic reionization, using deep spectral data from the JADES survey.

Contribution

First detection of 12 new AGN at 4<z<7 with evidence for merging black holes and probing low-mass regimes, advancing understanding of early black hole formation and growth.

Findings

Black hole masses range from 4x10^5 to 8x10^7 Msun.

Most black holes accrete at sub-Eddington rates, but smaller ones can be super-Eddington.

Early black holes are over-massive relative to their host galaxies but align with local velocity dispersion relations.

Abstract

We present 12 new AGN at 4<z<7 in the JADES survey (in addition to the previously identified AGN in GN-z11 at z=10.6) revealed through the detection of a Broad Line Region as seen in Halpha. The depth of JADES, together with the use of three different spectral resolutions, enables us to probe a lower mass regime relative to previous studies. In a few cases we find evidence for two broad components of Halpha which suggests that these could be candidate merging black holes (BHs). The inferred BH masses range between 8 x 10^7 Msun down to 4 x 10^5 Msun, interestingly probing the regime expected for Direct Collapse Black Holes (DCBHs). The inferred AGN bolometric luminosities (~10^44-10^45 erg/s) imply accretion rates that are < 0.5 times the Eddington rate in most cases. However, small BHs, with M_BH ~ 10^6 Msun, tend to accrete at Eddington or super-Eddington rates. These BH at z~4-11 are over-massive relative to their host galaxies stellar masses when compared to the local M_BH-Mstar relation, and even approaching M_BH~Mstar, as expected for DCBHs and super-Eddington scenarios. However, we find that these early BHs tend to be more consistent with the local relation between M_BH and velocity dispersion, as well as between M_BH and dynamical mass, suggesting that these are more fundamental and universal relations. On the BPT excitation-diagnostic diagram these AGN are located in the region that is that is locally occupied by star-forming galaxies, implying that they would be missed by the standard classification techniques if they did not display broad lines. Their location on the diagram is consistent with what expected for AGN hosted in metal poor galaxies (Z ~ 0.1-0.2 Zsun). The fraction of broad line AGN with L_AGN > 10^44 erg/s, among galaxies in the redshift range 4<z<6, is about 10%, suggesting that the contribution of AGN and their hosts to the reionization of the Universe is > 10%.