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 ] λ λ 1907, 1909, [O ii ] λ 3727, [Ne iii ] λ 3869, [Ne iii ] λ 3968, H δ λ 4101, H γ λ 4340, and [O iii ] λ 4363. 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) Z _⊙, ionization parameter log (U) = −1.9 ± 0.2, and an ionizing photon production efficiency log (ξ ion) = 25.2 ± 0.2 erg⁻¹ Hz. The spectrum has a softened Ly α break, evidence for a strong Ly α damping wing. The Ly α 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 / M _⊙) = 8.1 ± 0.3, including ∼6 × 10⁷ M _⊙ in component A, most of which formed recently (within ∼20 Myr) with a star formation rate ∼ 2 ± 1 M _⊙ 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. [ABSTRACT FROM AUTHOR]