GA-NIFS: JWST/NIRSpec IFU observations of HFLS3 reveal a dense galaxy group at z~6.3

G. C. Jones; H. Ubler; M. Perna; S. Arribas; A. J. Bunker; S. Carniani; S. Charlot; R. Maiolino; B. Rodriguez Del Pino; C. Willott; R. A. A. Bowler; T. Boker; A. J. Cameron; J. Chevallard; G. Cresci; M. Curti; F. D'Eugenio; N. Kumari; A. Saxena; J. Scholtz; G. Venturi; J. Witstok

arXiv · 2308.16620

GA-NIFS: JWST/NIRSpec IFU observations of HFLS3 reveal a dense galaxy group at z~6.3

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Abstract

Massive, starbursting galaxies in the early Universe represent some of the most 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 with mild gravitational magnification ($\mu$~2.2). Here, we present new observations of HFLS3 with the JWST/NIRSpec IFU in both low (PRISM/CLEAR; R~100) and high spectral resolution (G395H/290LP; R~2700), with high spatial resolution (~0.1") and sensitivity. Thanks to the combination of the NIRSpec data and a new lensing 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 to the 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 and morpho-kinematic maps for each bright emission line from the R2700 data for all sources except G2. From a line ratio analysis, the galaxies in component C are likely powered by star formation, while we cannot rule out or confirm the presence of AGN in the other high-redshift sources. We perform gravitational lens modelling, finding evidence for a two-source composition of the lensed central object and a comparable magnification factor ($\mu$=2.1-2.4) to previous work. The projected distances and velocity offsets of each galaxy suggest that they will merge within the next ~1Gyr. Finally, we examine the dust extinction-corrected SFR(Ha) of each z>6 source, finding that the total star formation ($510\pm140$Msol/yr, magnification-corrected) is distributed across 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, but instead is a merging system of star-forming galaxies in the Epoch of Reionisation.

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G. C. Jones, H. Ubler, M. Perna, S. Arribas, A. J. Bunker, S. Carniani, S. Charlot, R. Maiolino, B. Rodriguez Del Pino, C. Willott, R. A. A. Bowler, T. Boker, A. J. Cameron, J. Chevallard, G. Cresci, M. Curti, F. D'Eugenio, N. Kumari, A. Saxena, J. Scholtz, G. Venturi, J. Witstok. 2023-08-31. GA-NIFS: JWST/NIRSpec IFU observations of HFLS3 reveal a dense galaxy group at z~6.3. https://arxiv.org/abs/2308.16620

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