The Dual Nature of GHZ9: Coexisting Active Galactic Nuclei and Star Formation Activity in a Remote X-Ray Source at z = 10.145

August 2025 • 2025ApJ...989...75N

Authors • Napolitano, Lorenzo • Castellano, Marco • Pentericci, Laura • Vignali, Cristian • Gilli, Roberto • Fontana, Adriano • Santini, Paola • Treu, Tommaso • Calabrò, Antonello • Llerena, Mario • Piconcelli, Enrico • Zappacosta, Luca • Mascia, Sara • Tripodi, Roberta • Arrabal Haro, Pablo • Bergamini, Pietro • Bakx, Tom J. L. C. • Dickinson, Mark • Glazebrook, Karl • Henry, Alaina • Leethochawalit, Nicha • Mazzolari, Giovanni • Merlin, Emiliano • Morishita, Takahiro • Nanayakkara, Themiya • Paris, Diego • Puccetti, Simonetta • Roberts-Borsani, Guido • Rojas Ruiz, Sofia • Rosati, Piero • Vanzella, Eros • Vito, Fabio • Vulcani, Benedetta • Wang, Xin • Yoon, Ilsang • Zavala, Jorge A.

Abstract • 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.

Links

• PDF https://iopscience.iop.org/article/10.3847/1538-4357/ade706/pdf
• PREPRINT http://arxiv.org/abs/2410.18763
• DATA https://archive.stsci.edu/mastbibref.php?bibcode=2025ApJ...989...75N
• DATA https://archive.stsci.edu/mastbibref.php?bibcode=2025ApJ...989...75N
• DATA https://cda.harvard.edu/chaser?obsid=7712,7915,8477,8557,25277,25278,25279,25907,25908,25909,25910,25911,25912,25913,25914,25915,25916,25917,25918,25919,25920,25921,25922,25923,25924,25925,25926,25927,25928,25929,25930,25931,25932,25933,25934,25935,25936,25937,25938,25939,25940,25941,25942,25943,25944,25945,25946,25947,25948,25949,25950,25951,25952,25953,25954,25955,25956,25957,25958,25959,25960,25961,25962,25963,25964,25965,25966,25967,25968,25969,25970,25971,25972,25973,26280,27347,27449,27450,27556,27563,27575,27678,27679,27680,27681,27739,27780,27856,27857,27896,27974,28370,28483,28872,28886,28887,28910,28920,28934,28951,28952
• DATA https://doi.org/10.17909/4r6b-bx96
• DATA https://doi.org/10.25574/cdc.386
• ELECTR https://doi.org/10.3847/1538-4357/ade706