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Arxiv: GA-NIFS: ISM properties and metal enrichment in a merger-driven starburst during the Epoch of Reionisation probed with JWST and ALMA Published: 11/12/2024 12:18:11 PM Updated: 11/12/2024 12:18:11 PM

Paper abstract: We present deep JWST/NIRSpec integral-field spectroscopy (IFS) and ALMA[CII]\lambda158\mum observations of COS-3018, a star-forming galaxy atz~6.85, as part of the GA-NIFS programme. Both G395H (R~ 2700) andPRISM (R~ 100) NIRSpec observations revealed that COS-3018 is comprised ofthree separate components detected in [OIII]\lambda5008, which we dub asMain, North and East, with stellar masses of 10^{9.4 \pm 0.1}, 10^{9.2 \pm0.07}, 10^{7.7 \pm 0.15} M_{\odot}. We detect [OIII]\lambda5008,[OIII]\lambda\lambda3727,29 and multiple Balmer lines in all three componentstogether with [OIII]\lambda4363 in the Main and North components. This allowsus to measure an ISM temperature of T_{e}= 1.27\pm0.07\times 10^4 andT_{e}= 1.6\pm0.14\times 10^4 K with densities of n_{e} = 1250\pm250 andn_{e} = 700\pm200 cm^{-3}, respectively. These deep observations allow usto measure an average metallicity of 12+log(O/H)=7.9--8.2 for the threecomponents with the T_{e}-method. We do not find any significant evidence ofmetallicity gradients between the components. Furthermore, we also detect[NII]\lambda6585, one of the highest redshift detections of this emissionline. We find that in a small, metal-poor clump 0.2 arcsec west of the Northcomponent, N/O is elevated compared to other regions, indicating that nitrogenenrichment originates from smaller substructures, possibly proto-globularclusters. [OIII]\lambda5008 kinematics show that this system is merging,which is probably driving the ongoing, luminous starburst.