JADES: A large population of obscured, narrow-line active galactic nuclei at high redshift

Abstract

We present the identification of 41 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 allowed us to select narrow-line AGN 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 used high ionisation lines, such as He IIλ4686, He IIλ1640, [Ne IV] λ2422, [Ne V] λ3420, and N V λ1240, also in combination with other UV transitions, to trace the presence of AGN. Out of a parent sample of 209 galaxies, we identified 42 type-2 AGN (although ten of them are tentative), making the fraction of galaxies in JADES hosting type-2 AGN about 20 ± 5%, which does not evolve significantly in the redshift range between 2 and 10. The selected type-2 AGN have estimated bolometric luminosities of 1041.3 - 44.9 erg s-1 and host-galaxy stellar masses of 107.2 - 9.3 M⊙. 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 ∼18- 30% to the UV luminosity function across different UV luminosity bins, increasing slightly with UV luminosity.