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 5 galaxies, dubbed JWST’s Quintet (JQ), at redshift 6.7. This system resides in a small area of approximately 4.5″ × 4.5″ (24.6 × 24.6 pkpc²), containing over 17 galaxy-size clumps with a total stellar mass of 10¹⁰ M_⊙. JQ has a total star formation rate of 255 M_⊙ yr⁻¹, placing it approximately 1 dex above the star formation rate–mass main sequence at this epoch. The high mass and star formation rate of JQ 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] + Hβ gaseous halo surrounding and connecting four galaxies in JQ, suggesting the existence of metals in the surrounding medium—the inner part of its circumgalactic medium. This provides direct evidence for metal enrichment of galaxies’ environments through merger-induced tidal stripping, just 800 Myr after the Big Bang.