2025ApJ...989...75N

We present James Webb Space Telescope (JWST)/NIRSpec PRISM spectroscopic characterization of GHZ9 at z = 10.145 ± 0.010, currently the most distant source detected by the Chandra X-ray Observatory. The spectrum reveals several UV high-ionization lines, including C II, Si IV, N IV], C IV, He II, O III], N III], and C III]. The prominent rest-frame equivalent widths (EW(C IV) ≃ 65 Å, EW(O III]) ≃ 28 Å, and EW(C III]) ≃ 48 Å) show the presence of a hard active galactic nucleus (AGN) radiation field, while line ratio diagnostics are consistent with either AGN or star formation as the dominant ionizing source. GHZ9 is nitrogen-enriched (6-9.5 (N/O)_⊙), carbon-poor (0.2-0.65 (C/O)_⊙), metal-poor (Z = 0.01-0.1 Z_⊙), and compact (<106 pc), similarly to GN-z11, GHZ2, and recently discovered N-enhanced high redshift objects. We exploited the newly available JWST/NIRSpec and NIRCam data set to perform an independent analysis of the Chandra data confirming that GHZ9 is the most likely JWST source associated with X-ray emission at 0.5-7 keV. Assuming a spectral index Γ = 2.3 (1.8), we estimate a black hole (BH) mass of 1.60 ± 0.31 (0.48 ± 0.09) × 10⁸M_⊙, which is consistent either with Eddington-accretion onto heavy (≥10⁶M_⊙) BH seeds formed at z = 18 or super-Eddington accretion onto a light seed of ∼10²-10⁴M_⊙at z = 25. The corresponding BH-to-stellar mass ratio M_BH/M_star = 0.33 ± 0.22 (0.10 ± 0.07), with a stringent limit >0.02, implies an accelerated growth of the BH mass with respect to the stellar mass. GHZ9 is the ideal target to constrain the early phases of AGN-galaxy coevolution with future multifrequency observations.