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Arxiv: JADES: The star-formation and chemical enrichment history of a luminous galaxy at z~9.43 probed by ultra-deep JWST/NIRSpec spectroscopy Published: 7/2/2024 9:00:32 PM Updated: 7/2/2024 9:00:32 PM

Paper abstract: We analyse ultra-deep JWST observations of the galaxy JADES-GS-z9-0 at z =9.4327, and derive detailed stellar and interstellar medium (ISM) properties ofthis luminous (MUV=-20.43) high-redshift system. Complementary information fromNIRCam imaging and NIRSpec (both low- and medium-resolution) spectroscopyreveal a compact system (Re ~110 pc) characterised by a steeply rising starformation history, which is reflected in the inferred young stellar age (t ~ 3Myr, light-weighted), high star-formation rate surface density ({\Sigma}SFR ~72 M yr-1 kpc-2), high ionisation parameter (log(U) ~ -1.5), low metallicity(12+log(O/H) ~ 7.5), and low carbon-over-oxygen abundance ([C/O] = -0.64).Leveraging the detection of N iii]1750 we derive nitrogen-over-oxygen abundance([N/O] ~ 0) higher than the plateau followed by low-redshift galaxies ofsimilar metallicity, possibly revealing the imprint from (very) massive starson the ISM enrichment and favouring a top-heavy Initial Mass Function (IMF)scenario. Massive stars powering a hard radiation field are also required toexplain the rest-frame UV line ratios, though the presence of thehigh-excitation [Ne v]{\lambda}3426 emission line possibly hints at additionalionization from an AGN. We also report the tentative detection of Ly{\alpha}emission in the G140M spectrum, shifted by ~450 km/s redward of the systemicredshift. Combined with a modelling of the Ly{\alpha} spectral break, we ruleout the presence of very high column densities of neutral gas pertaining tolocal absorbers, as well as any extended surrounding ionised bubble, suggestingthat JADES-GS-z9-0 has not yet significantly contributed to cosmicReionization.