James Webb Space Telescope Feed Post

JWST NIRSpec Spectroscopy of the Remarkable Bright Galaxy GHZ2/GLASS-z12 at Redshift 12.34

Observed 2D (top) and 1D (bottom) NIRSpec PRISM spectra of GHZ2. In the bottom panel the gray line shows the noise RMS, and red dashed lines highlight the wavelength of the UV features discussed in the present paper. Abstract: We spectroscopically confirm the MUV=-20.5 mag galaxy GHZ2/GLASS-z12 to be at redshift z=12.34. The source was selected via NIRCam photometry in GLASS-JWST Early Release Science data, providing the first evidence of a surprising abundance of bright galaxies at z?10. The NIRSpec PRISM spectrum is remarkable and unlike any local analog. It shows significant detections of N IV, C IV, He II, O III, C III, O II, and Ne III lines, and the first detection in a high-redshift object 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 characterised by hard radiation fields. GHZ2 displays UV lines with EWs that are only found in active galactic nuclei (AGNs) or composite objects at low/intermediate redshifts, and UV line-intensity ratios that are compatible both with AGNs and star formation in a low-metallicity environment. The nondetection of the very high-ionization lines [Ne IV] and [Ne V], 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 low metallicity, massive stars forming in a dense environment. We estimate a metallicity ?0.1Z/Z?, 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 at high redshift. Considering its abundance patterns and the high stellar mass density (104 M? 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.