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Arxiv: JWST NIRSpec Spectroscopy of the Remarkable Bright Galaxy GHZ2/GLASS-z12 at Redshift 12.34 Published: 3/15/2024 2:12:44 PM Updated: 3/15/2024 2:12:44 PM

Paper abstract: We spectroscopically confirm the M_{\rm UV} = -20.5 mag galaxyGHZ2/GLASS-z12 to be at redshift z=12.34. The source was selected via NIRCamphotometry in GLASS-JWST Early Release Science data, providing the firstevidence of a surprising abundance of bright galaxies at z \gtrsim 10. TheNIRSpec PRISM spectrum is remarkable and unlike any local analog. It showssignificant detections of N IV, C IV, He II, O III, C III, O II, and Ne IIIlines, and the first detection in a high-redshift object of the O III Bowenfluorescence line at 3133 {\AA} rest-frame. The prominent C IV line withrest-frame equivalent width (EW) ~ 46 {\AA} puts GHZ2 in the category ofextreme C IV emitters characterised by hard radiation fields. GHZ2 displays UVlines with EWs that are only found in active galactic nuclei (AGNs) orcomposite objects at low/intermediate redshifts, and UV line-intensity ratiosthat are compatible both with AGNs and star formation in a low-metallicityenvironment. The nondetection of the very high-ionization lines [Ne IV] and [NeV], and the remarkable similarity between GHZ2 and other known C IV emitters,favors a scenario in which the high ionizing output is due to very lowmetallicity, massive stars forming in a dense environment. We estimate ametallicity <~ 0.1 Z/{\rm Z}_{\odot}, a high ionization parameter logU> -2, a N/O abundance 4--5 times the solar value, and a subsolar C/O ratiosimilar to the recently discovered class of nitrogen-enhanced objects at highredshift. Considering its abundance patterns and the high stellar mass density(10^4 M_{\odot} pc^{-2}), GHZ2 is an ideal formation site for theprogenitors of today's globular clusters. The remarkable brightness of GHZ2makes it a "Rosetta stone" for understanding the physics of galaxy formationwithin just 360 Myr after the Big Bang.