The eventful life of a luminous galaxy at z = 14: metal enrichment, feedback, and low gas fraction?

JADES-GS-z14-0 is the most distant spectroscopically confirmed galaxy so far, at $z > 14$ . With a UV magnitude of $-20.81$ , it is one of the most luminous galaxies at cosmic dawn and its half-light radius of $260\ \mathrm{pc}$ means that stars dominate the observed UV emission. We report the ALMA detection of $\mathrm{[OIII]}88\mu\mathrm{m}$ line emission with a significance of $6.67\sigma$ and at a frequency of $223.524\ \mathrm{GHz}$ , corresponding to a redshift of $14.1796 \pm 0.0007$ , which is consistent with the candidate $\mathrm{CIII]}$ line detected in the NIRSpec spectrum. At this spectroscopic redshift, the Lyman break identified with NIRSpec requires a damped $\mathrm{Lyman}-\alpha$ absorber with a column density of $\mathrm{log}_{10}(N_{\mathrm{HI}}/\mathrm{cm}^{2}) = 22.23$ . The total $\mathrm{[OIII]}88\mu\mathrm{m}$ luminosity ($\mathrm{log}_{10}(L_{\mathrm{[OIII]}}/L_{\odot}) = 8.3 \pm 0.1$ ) is fully consistent with the local $L_{\mathrm{[OIII]}}-\mathrm{SFR}$ relation. Based on the $L_{\mathrm{[OIII]}}/\mathrm{SFR}$ , we infer a gas-phase metallicity $> 0.1\ Z_{\odot}$ , which is somewhat unexpected given the weakness of the UV emission lines. Using prospector SED modeling and combining the ALMA data with JWST observations, we find $Z = 0.17\ Z_{\odot}$ and an escape fraction of ionizing photons of $20\%$ , which is necessary to explain the UV spectrum. We measure an $\mathrm{[OIII]}5007\mathrm{\AA}/\mathrm{[OIII]}88\mu\mathrm{m}$ line flux ratio between $1$ and $10$ , resulting in an upper limit to the electron density of roughly $300\ \mathrm{cm}^{-3}$ , which is lower than those measured in other $\mathrm{high}-z$ luminous galaxies. The $\mathrm{[OIII]}88\mu\mathrm{m}$ emission line is spectrally resolved, with a FWHM of $100\ \mathrm{km/s}$ , resulting in a dynamical mass of $\mathrm{log}_{10}(M_{\mathrm{dyn}}/M_{\odot}) = 9.0 \pm 0.2$ . This value is comparable to the stellar mass derived from the SED fitting, which implies a very low gas fraction. Past radiation-driven outflows may have cleared the galaxy from the gas, reducing the gas fraction and thus increasing the escape fraction of ionizing photons.

eprint arXiv:2409.20533