James Webb Space Telescope Feed Post

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

Paper abstract: 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 pc means that stars dominate the observed UV emission. We report the ALMA detection of [OIII]88\mum line emission with a significance of 6.67\sigma and at a frequency of 223.524 GHz, corresponding to a redshift of 14.1796\pm0.0007, which is consistent with the candidate CIII] line detected in the NIRSpec spectrum. At this spectroscopic redshift, the Lyman break identified with NIRSpec requires a damped Lyman-\alpha absorber with a column density of \log(N_{\rm HI}/\mathrm{cm}^{-2})=22.23. The total [OIII]88\mum luminosity (log((L_{\rm [OIII]}/L_\odot) = 8.3\pm0.1) is fully consistent with the local L_{\rm [OIII]}-SFR relation. Based on the {L_{\rm [OIII]}/SFR}, we infer a gas-phase metallicity >0.1~{\rm Z_{\rm \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_{\rm \odot}} and an escape fraction of ionizing photons of 20%, which is necessary to explain the UV spectrum. We measure an [O III]5007\r{A}/[O III]88\mum line flux ratio between 1 and 10, resulting in an upper limit to the electron density of roughly 300 cm^{-3}, which is lower than those measured in other high-z luminous galaxies. The [OIII]88\mum emission line is spectrally resolved, with a FWHM of 100 km/s, resulting in a dynamical mass of \log(M_{\rm dyn}/M_\odot) = 9.0\pm0.2. 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.