JADES: Nitrogen Enhancement in High-Redshift Broad-Line Active Galactic Nuclei

TL;DR

This study investigates the link between nitrogen enrichment and black hole formation in high-redshift AGNs, revealing dense, nitrogen-rich gas in broad-line AGNs and proposing a connection to early black hole seeding within proto-globular clusters.

Contribution

It provides new evidence of nitrogen-rich, dense gas in high-z broad-line AGNs and suggests a novel connection between nitrogen enrichment, dense star formation, and early black hole seed formation.

Findings

Nitrogen-rich, dense gas detected in high-z broad-line AGNs.

Evidence linking nitrogen enrichment to proto-globular cluster star formation.

Support for models connecting black hole seeds to stellar collisions in early clusters.

Abstract

The unexpectedly high nitrogen-to-oxygen (N/O) ratios observed in high-redshift (z) galaxies have challenged our understanding of early star formation. Notably, many of these nitrogen-rich galaxies show signatures of active galactic nuclei (AGNs), suggesting a possible connection between black hole formation and nitrogen enrichment. To explore this connection, we analyse stacked spectra of z=4-7 broad-line and narrow-line AGNs using deep NIRSpec data from the JADES survey. We identify a significant Niii] quintuplet and a high electron density ($\sim10^{4}\,\mathrm{cm^{-3}}$) only in the broad-line AGN stack, indicating nitrogen-rich ($\log(\mathrm{N/C})\simeq0.5$, $\log(\mathrm{N/O})>-0.6$) and dense gas similar to the high-z nitrogen-rich galaxies. Our findings suggest that dense nuclear star formation may trap nitrogen-rich gas in proto-globular clusters, in line with the high N/O observed in local globular clusters; associated runaway stellar collisions could produce intermediate-mass black hole seeds, as predicted by some models and simulations, whose accretion results into AGN signatures. These findings support scenarios connecting the early black hole seeding and growth to merging processes within and between proto-globular clusters in primeval galaxies.