JADES: A large population of obscured, narrow line AGN at high redshift

TL;DR

This paper identifies 42 high-redshift narrow-line AGN candidates using JWST/NIRSpec data, revealing their properties and prevalence up to z=10, and highlighting the importance of UV lines for AGN detection at early cosmic times.

Contribution

It introduces a novel method combining optical and UV emission lines to identify obscured AGN at high redshift, expanding the known population.

Findings

Approximately 20% of galaxies host type-2 AGN across z=2-10.

AGN host galaxies have stellar masses between 10^7.2 and 10^9.3 solar masses.

AGN contribute up to 30% of the UV luminosity at high redshift.

Abstract

We present the identification of 42 narrow-line active galactic nuclei (type-2 AGN) candidates in the two deepest observations of the JADES spectroscopic survey with JWST/NIRSpec. The spectral coverage and the depth of our observations allow us to select narrow-line AGNs based on both rest-frame optical and UV emission lines up to z=10. Due to the metallicity decrease of galaxies, at $z>3$ the standard optical diagnostic diagrams (N2-BPT or S2-VO87) become unable to distinguish many AGN from other sources of photoionisation. Therefore, we also use high ionisation lines, such as HeII$\lambda$4686, HeII$\lambda$1640, NeIV$\lambda$2422, NeV$\lambda$3420, and NV$\lambda$1240, also in combination with other UV transitions, to trace the presence of AGN. Out of a parent sample of 209 galaxies, we identify 42 type-2 AGN (although 10 of them are tentative), giving a fraction of galaxies in JADES hosting type-2 AGN of about $20\pm3$\%, which does not evolve significantly in the redshift range between 2 and 10. The selected type-2 AGN have estimated bolometric luminosities of $10^{41.3-44.9}$ erg s$^{-1}$ and host-galaxy stellar masses of $10^{7.2-9.3}$ M$_{\odot}$. The star formation rates of the selected AGN host galaxies are consistent with those of the star-forming main sequence. The AGN host galaxies at z=4-6 contribute $\sim$8-30 \% to the UV luminosity function, slightly increasing with UV luminosity.