Extended Enriched Gas in a Multi-Galaxy Merger at Redshift 6.7

Abstract

Recent JWST observations have uncovered high-redshift galaxies characterized by multiple star-forming clumps, many of which appear to be undergoing mergers. Such mergers, especially those of two galaxies with equivalent masses, play a critical role in driving galaxy evolution and regulating the chemical composition of their environments. Here, we report a major merger of at least five galaxies, dubbed JWST's Quintet (JQ), at redshift 6.7, discovered in the JWST GOODS-South field. This system resides in a small area $\sim4.5''\times4.5''$ ($24.6\times24.6$ pkpc$^2$), containing over 17 galaxy-size clumps with a total stellar mass of $10^{10}\ M_\odot$. The JQ system has a total star formation rate of 240 -- 270 $M_\odot$ yr$^{-1}$, placing it $\sim1$ dex above the median star formation rate-mass main sequence at this epoch. The high mass and star formation rate of the JQ galaxies are consistent with the star formation history of those unexpected massive quiescent galaxies observed at redshift 4-5, offering a plausible evolutionary pathway for the formation of such galaxies. We also detect a large [O III]+H$\beta$ emitting gaseous halo surrounding and connecting four galaxies in the JQ, suggesting the existence of heavy elements in the surrounding medium -- inner part of its circumgalactic medium (CGM). This provides direct evidence for the metal enrichment of galaxies' environments through merger-induced tidal stripping, just 800 Myr after the Big Bang.