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Literature
Date: 12/4/2023

Arxiv: GA-NIFS: JWST/NIRSpec IFU observations of HFLS3 reveal a dense galaxy group at z~6.3 Published: 8/31/2023 1:28:16 PM Updated: 12/1/2023 7:10:37 PM

Paper abstract: Massive, starbursting galaxies in the early Universe represent some of themost extreme objects in the study of galaxy evolution. One such source is HFLS3(z~6.34), which was originally identified as an extreme starburst galaxy withmild gravitational magnification (\mu~2.2). Here, we present new observationsof HFLS3 with the JWST/NIRSpec IFU in both low (PRISM/CLEAR; R~100) and highspectral resolution (G395H/290LP; R~2700), with high spatial resolution (~0.1")and sensitivity. Thanks to the combination of the NIRSpec data and a newlensing model with accurate spectroscopic redshifts, we find that the 3"x3"field is crowded, with a lensed arc (C, z=6.3425\pm0.0002), two galaxies tothe south (S1 and S2, z=6.3592\pm0.0001), two galaxies to the west (W1,z=6.3550\pm0.0001; W2, z=6.3628\pm0.0001), and two low-redshift interlopers(G1, z=3.4806\pm0.0001; G2, z=2.00\pm0.01). We present spectral fits andmorpho-kinematic maps for each bright emission line from the R2700 data for allsources except G2. From a line ratio analysis, the galaxies in component C arelikely powered by star formation, while we cannot rule out or confirm thepresence of AGN in the other high-redshift sources. We perform gravitationallens modelling, finding evidence for a two-source composition of the lensedcentral object and a comparable magnification factor (\mu=2.1-2.4) toprevious work. The projected distances and velocity offsets of each galaxysuggest that they will merge within the next ~1Gyr. Finally, we examine thedust extinction-corrected SFR(Ha) of each z>6 source, finding that the totalstar formation (510\pm140Msol/yr, magnification-corrected) is distributedacross the six z~6.34-6.36 objects over a region of diameter ~11kpc.Altogether, this suggests that HFLS3 is not a single starburst galaxy, butinstead is a merging system of star-forming galaxies in the Epoch ofReionisation.