JADES: Carbon enrichment 350 Myr after the Big Bang

¹ Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
² Cavendish Laboratory, University of Cambridge, 19 JJ Thomson Avenue, Cambridge CB3 0HE, UK
³ Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
⁴ Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126 Pisa, Italy
⁵ Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
⁶ Centre for Astrophysics Research, Department of Physics, Astronomy and Mathematics, University of Hertfordshire, Hatfield AL10 9AB, UK
⁷ Sorbonne Université, CNRS, UMR 7095, Institut d’Astrophysique de Paris, 98 bis bd Arago, 75014 Paris, France
⁸ Centro de Astrobiología (CAB), CSIC-INTA, Cra. de Ajalvir Km. 4, 28850 Torrejón de Ardoz, Madrid, Spain
⁹ School of Physics, University of Melbourne, Parkville, 3010 VIC, Australia
¹⁰ ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), Australia
¹¹ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
¹² Center for Astrophysics | Harvard & Smithsonian, 60 Garden St., Cambridge, MA 02138, USA
¹³ Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA
¹⁴ AURA for European Space Agency, Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21210, USA
¹⁵ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
¹⁶ Department for Astrophysical and Planetary Science, University of Colorado, Boulder, CO 80309, USA
¹⁷ Department of Astronomy and Astrophysics, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, USA
¹⁸ Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK
¹⁹ NRC Herzberg, 5071 West Saanich Rd, Victoria, BC V9E 2E7, Canada

Received: 16 November 2023
Accepted: 24 April 2024

Abstract

Finding the emergence of the first metals in the early Universe and identifying their origin are some of the most important goals of modern astrophysics. We present deep JWST/NIRSpec spectroscopy of GS-z12, a galaxy at z = 12.5, in which we report the detection of the C III]λλ1907,1909 nebular emission line. This represents the most distant detection of a metal transition, and the most distant redshift determination based on emission lines. In addition, we report tentative detections of [O II]λλ3726,3729 and [Ne III]λ3869, and possibly O III]λλ1661,1666. By using the accurate redshift obtained from C III], we can model the Lyα drop to reliably measure an absorbing column density of hydrogen of N_H I ≈ 10²² cm⁻², which is too high for an IGM origin and implies an abundant neutral ISM in GS-z12 or in the CGM around it. We tentatively infer a lower limit for the neutral gas mass of about 10⁷ M_⊙ which, compared with the galaxy stellar mass of ∼5 × 10⁷ M_⊙, implies a gas fraction higher than about 0.2–0.5. By comparing the measured emission lines with model-based diagnostic diagrams, we derive a solar or even super-solar carbon-to-oxygen ratio, tentatively log (C/O) >  − 0.21 dex ([C/O] > 0.15 dex), while a Bayesian modelling of the spectrum indicates log (C/O) = − 0.30 ± 0.07 dex ([C/O] = 0.06 ± 0.07 dex). This is higher than the C/O measured in galaxies discovered by JWST at z = 6 − 9, and higher than the C/O arising from Type II supernovae enrichment. Asymptotic giant branch stars can hardly contribute to the observed carbon enrichment at these early epochs and low metallicities. Such a high C/O in a galaxy observed 350 Myr after the Big Bang may thus be explained by the yields of extremely metal-poor stars, and may even be the heritage of the first generation of supernovae from Population III progenitors. A robust determination of the total metallicity in this galaxy is essential to constrain these scenarios.