JWST NIRSpec spectroscopy of the triply lensed z = 10.17 galaxy MACS0647–JD

We present JWST/NIRSpec prism spectroscopy of MACS0647−JD, a triply lensed z ∼ 11 candidate discovered in Hubble Space Telescope imaging and spatially resolved by JWST imaging into two components, A and B. Spectroscopy of component A yields a spectroscopic redshift z = 10.17 based on seven detected emission lines: C III] λλ1907, 1909, [O II] λ3727, [Ne III] λ3869, [Ne III] λ3968, Hδ λ4101, Hγ λ4340, and [O III] λ4363. These are the second-most distant detections of these emission lines to date, in a galaxy observed just 460 million years after the Big Bang. Based on observed and extrapolated line flux ratios we derive a gas-phase metallicity 12 + log (O/H) ∼ 7.5–8.0, or Z ∼ (0.06–0.2) Ze, ionization parameter log(U) = −1.9 ± 0.2, and an ionizing photon production efficiency log 25.2 ± 0.2 erg-1 Hz. The spectrum has a softened Lyα break, evidence for a strong Lyα damping wing. The Lyα damping wing also suppresses the F150W photometry, explaining the slightly overestimated photometric redshift z = 10.6 ± 0.3. MACS0647−JD has a stellar mass log(M/Me) = 8.1 ± 0.3, including ∼6 × 10 7 Me in component A, most of which formed recently (within ∼20 Myr) with a star formation rate ∼ 2 ± 1 Me yr−1 , all within an effective radius 70 ± 24 pc. Spectroscopy of a fainter companion galaxy C separated by a distance of ∼ 3 kpc reveals a Lyman break consistent with z ∼ 10.17. MACS0647−JD is likely the most distant galaxy merger known.