JADES: Carbon enrichment 350 Myr after the Big Bang in a gas-rich galaxy

Abstract: Finding the emergence of the first generation of 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 C III]${\lambda}{\lambda}$1907,1909 nebular emission. This is the most distant detection of a metal transition and the most distant redshift determination via emission lines. In addition, we report tentative detections of [O II]${\lambda}{\lambda}$3726,3729 and [Ne III]${\lambda}$3869, and possibly O III]${\lambda}{\lambda}$1661,1666. By using the accurate redshift from C III], we can model the Ly${\alpha}$ drop to reliably measure an absorbing column density of hydrogen of $N_{HI} \approx 10^{22}$ cm$^{-2}$ - too high for an IGM origin and implying abundant ISM in GS-z12 or CGM around it. We infer a lower limit for the neutral gas mass of about $10^7$ MSun which, compared with a stellar mass of $\approx4 \times 10^7$ MSun inferred from the continuum fitting, implies a gas fraction higher than about 0.1-0.5. We derive a solar or even super-solar carbon-to-oxygen ratio, tentatively [C/O]>0.15. 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, while AGB stars cannot contribute to 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 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.

• The paper reports the detection of remote CIII] emissions in GS-z12, marking the most distant metal transition observed 350 Myr post-Big Bang.
• It applies Bayesian spectral analysis to JWST NIRSpec data, extracting key parameters like stellar mass, SFR, and dust attenuation.
• The findings challenge conventional enrichment models by revealing a super-solar [C/O] ratio, hinting at non-standard early star formation processes.

Analysis of High-Redshift Metallicity and Gas Dynamics in GS-z12 via JWST Observations

In exploring the early Universe's chemical evolution, understanding the emergence of metals and the enrichment processes of galaxies is of critical importance. The study by D’Eugenio et al. utilizes the observations from the James Webb Space Telescope (JWST) Near InfraRed Spectrograph (NIRSpec) to detail the properties of GS-z12, a galaxy situated at a redshift of z = 12.5. This study reports the detection of Ciii]λλ1907, 1909 emission lines, marking it as the most remote metal transition ever observed and providing us with new insights into the conditions prevalent merely 350 million years after the Big Bang.

Core Findings

The researchers applied a detailed spectral analysis using the Bayesian modeling tool beagle to extract physical properties of GS-z12. Key parameters include a stellar mass M⋆ = 4 × 10⁷ M⊙, a star formation rate (SFR) of 1.15 ± 0.15 M⊙ yr⁻¹, and a pronounced dust attenuation optical depth τV = 0.12 ± 0.04, with a corresponding 12 + log(O/H) = 7.9 ± 0.2. The detection of these Ciii] emissions implies a minimum carbon-to-oxygen ratio [C/O] > 0.15 dex, suggesting super-solar abundances.

The researchers also inferred from the Lyα drop a significant amount of neutral hydrogen, indicating abundant interstellar medium (ISM) or circum-galactic medium (CGM). The inferred neutral hydrogen column density is NHI ≈ 10²² cm⁻², suggesting a high gas fraction in GS-z12, which is consistent with other high-redshift galaxies.

Methodological Approach

The study combines NIRSpec Micro-Shutter Assembly (MSA) spectroscopy with deep multi-band imaging from JWST programs to reach unparalleled spectroscopic depths. Various models are employed to interpret the photometric and spectroscopic observations, including local pixel-integrated Gaussian models for emission-line analysis and comparative abundance modeling contrasting different ionization sources like AGNs and star-forming regions.

Significance and Implications

The implications of detecting such distant metal transitions extend beyond mere redshift records. The super-solar [C/O] ratio challenges the common understanding that early galactic chemical evolution is dominated by Type-II supernova yields, which normally predict sub-solar C/O ratios. Instead, these findings highlight non-standard enrichment processes, possibly involving Population III supernovae, which could have left behind atypical abundance signatures rich in carbon.

Furthermore, with GS-z12's high SFR combined with significant gas fractions, the study also offers a backdrop for discussing the Schmidt–Kennicutt relation in early cosmic epochs. The observed SFR density suggests either a substantial molecular gas component not accounted for or an overestimation of star-formation rates based on current models.

Future Outlook

The meticulous approach in revisiting cosmic chemical histories in GS-z12 serves as a foundational step for future investigations with JWST. Continued observation campaigns aiming at larger sample sizes could help establish whether GS-z12’s characteristics are outliers or indicative of common conditions in early galaxies. Additionally, the findings encourage a re-evaluation of chemical evolution models to account for non-standard early Universe star formation and enrichment processes. As JWST observes more systems in this redshift regime, we should anticipate a more nuanced understanding of the Universe’s formative years, informing models of galaxy formation and evolution as well as chemical enrichment narratives.

In summary, the analysis undertaken by D’Eugenio and colleagues not only sets a new observational benchmark but also invites theoretical astrophysicists to consider the implications of non-traditional metal enrichment in shaping the galaxies of the early Universe. This paper pushes the envelope in how we perceive the interplay of star formation, supernova yields, and gas dynamics at cosmic dawn.