2024/03/15 by M. Castellano, Marco Castellano, Castellano, Marco +73 · 1 voice · 18 citations
Physics and Astronomy · Engineering · #Astronomy and Astrophysical Research #Stellar, planetary, and galactic studies #Astronomical Observations and Instrumentation
paper · pdf · doi:10.48550/arxiv.2403.10238
We spectroscopically confirm the M\rm UV = -20.5 mag galaxy GHZ2/GLASS-z12 to be at redshift z=12.34. The source was selected via NIRCam photometry in GLASS-JWST ERS data, providing the first evidence of a surprising abundance of bright galaxies at z \gtrsim 10. The NIRSpec PRISM spectrum shows detections of N IV, C IV, He II, O III, C III, O II, and Ne III lines, and the first detection at high-redshift of the O III Bowen fluorescence line at 3133 Å rest-frame. The prominent C IV line with rest-frame equivalent width (EW) ≈ 46 Å puts GHZ2 in the category of extreme C IV emitters. GHZ2 displays UV lines with EWs that are only found in active galactic nuclei (AGNs) or composite objects at low/intermediate redshifts. The UV line-intensity ratios are compatible both with AGNs and star formation in a low-metallicity environment, with the low limit on the [Ne IV]/[N IV] ratio favoring a stellar origin of the ionizing photons. We discuss a possible scenario in which the high ionizing output is due to low metallicity stars forming in a dense environment. We estimate a metallicity \lesssim 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 ratio similar to the recently discovered class of nitrogen-enhanced objects. Considering its abundance patterns and the high stellar mass density (104~M\odot~pc-2), GHZ2 is an ideal formation site for the progenitors of today's globular clusters. The remarkable brightness of GHZ2 makes it a ``Rosetta stone'' for understanding the physics of galaxy formation within just 360 Myr after the Big Bang.