James Webb Space Telescope Feed Post

Harvard ADS: The dual nature of GHZ9: coexisting AGN and star formation activity in a remote X-ray source at z=10.145

Paper abstract: We present JWST/NIRSpec PRISM spectroscopic characterization of GHZ9 at z= 10.145 \pm 0.010, currently the most distant source detected by the Chandra X-ray Observatory. The spectrum reveals several UV high-ionization lines, including CII, SiIV, [NIV], CIV, HeII, OIII], NIII], and CIII]. The prominent rest-frame equivalent widths (EW(CIV)~eq65A, EW(HeII)~eq18A, EW(CIII])~eq48A) show the presence of a hard radiation field, while the analysis of line ratio diagnostics suggest this galaxy hosts both AGN and star-formation activity. GHZ9 is nitrogen-enriched (6--9.5 times solar), carbon-poor (0.2--0.65 times solar), metal-poor (Z = 0.01--0.1 Z_{\odot}), and compact (< 106 pc), similarly to GNz11, GHZ2, and recently discovered N-enhanced high redshift objects. We exploited the newly available JWST/NIRSpec and NIRCam dataset to perform an independent analysis of the Chandra data confirming that GHZ9 is the most likely JWST source associated to X-ray emission at 0.5-7 keV. Assuming a spectral index \Gamma = 2.3 (1.8), we estimate a black hole (BH) mass of 1.60 \pm 0.31 (0.48 \pm 0.09) \times 10^8M_{\odot}, which is consistent either with Eddington-accretion onto heavy (>= 10^6 M_{\odot}) BH seeds formed at z=18, or super-Eddington accretion onto a light seed of ~ 10^2-10^4 M_{\odot} at z = 25. The corresponding BH-to-stellar mass ratio M_{BH}/M_{star}= 0.33\pm0.22 (0.10\pm0.07), 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 multi-frequency observations.