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Arxiv: JADES -- The Rosetta Stone of JWST-discovered AGN: deciphering the intriguing nature of early AGN Published: 7/11/2024 7:23:28 PM Updated: 10/16/2024 7:07:39 PM

Paper abstract: JWST has discovered a large population of Active Galactic Nuclei (AGN) athigh redshift. Many of these newly discovered AGN have broad permitted lines(typically H\alpha), but are extremely weak in the X-rays. Here we presentthe NIRSpec spectrum of the most extreme of these objects, GN-28074, an AGN atz=2.26 with prominent Balmer, Paschen and \HeI broad lines, and with thehighest limit on the bolometric to X-ray luminosity ratio among allspectroscopically confirmed AGN in GOODS. This source is also characterized bya mid-IR excess, most likely associated with the AGN torus' hot dust. The highbolometric luminosity and moderate redshift of this AGN allow us to explore itsproperties more in depth relative to other JWST-discovered AGN. The NIRSpecspectrum reveals prominent, slightly blueshifted absorption of H\alpha,H\beta and \HeI\lambda10830. The Balmer absorption lines require gas withdensities of n_{\rm H}> 10^8~{\rm cm}^{-3}, inconsistent with an ISM origin,but fully consistent with clouds in the Broad Line Region (BLR). This findingsuggests that at least part of the X-ray weakness is due to high (Comptonthick) X-ray absorption by (dust-free) clouds in the BLR, or in its outer,slowly outflowing regions. GN-28074 is also extremely radio-weak. The radioweakness can also be explained in terms of absorption, as the inferred densityof the clouds responsible for H\alpha absorption makes them optically thickto radio emission through free-free absorption. Alternatively, in this andother JWST-discovered AGN, the nuclear magnetic field may have not developedproperly yet, resulting both in intrinsically weak radio emission and also lackof hot corona, hence intrinsic X-ray weakness. Finally, we show that recentlyproposed scenarios, invoking hyper-dense and ultra-metal-poor outflows or Ramanscattering to explain the broad H\alpha, are completely ruled out.