RELICS: Small-scale Star Formation in Lensed Galaxies at z = 6–10

Abstract

Abstract Detailed observations of star-forming galaxies at high redshift are critical to understanding the formation and evolution of the earliest galaxies. Gravitational lensing provides an important boost, allowing observations at physical scales unreachable in unlensed galaxies. We present three lensed galaxies from the RELICS survey at z phot = 6–10, including the most highly magnified galaxy at z phot ∼ 6 (WHL 0137–zD1, dubbed the Sunrise Arc), the brightest known lensed galaxy at z phot ∼ 6 (MACS 0308–zD1), and the only spatially resolved galaxy currently known at z phot ∼ 10 (SPT 0615–JD). The Sunrise Arc contains seven star-forming clumps with delensed radii as small as 3 pc, the smallest spatial scales yet observed in a z > 6 galaxy, while SPT 0615–JD contains features measuring a few tens of parsecs. MACS 0308–zD1 contains an r ∼ 30 pc clump with a star formation rate (SFR) of ∼3 M ⊙ yr−1, giving it an SFR surface density of ΣSFR ∼ 103 M ⊙ yr−1 kpc−2. These galaxies provide a unique window into small-scale star formation during the epoch of reionization. They will be excellent targets for future observations with JWST, including one approved program targeting the Sunrise Arc.