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American Astronomical Society, Astrophysical Journal Letters, 2(949), p. L34, 2023

DOI: 10.3847/2041-8213/acc94b

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JWST Reveals a Possible z ∼ 11 Galaxy Merger in Triply Lensed MACS0647–JD

Journal article published in 2023 by Tiger Yu-Yang Hsiao ORCID, Dan Coe ORCID, Abdurro’uf ORCID, Lily Whitler ORCID, Intae Jung ORCID, Gourav Khullar ORCID, Ashish Kumar Meena ORCID, Pratika Dayal ORCID, Kirk S. S. Barrow ORCID, Lillian Santos-Olmsted ORCID, Adam Casselman ORCID, Eros Vanzella ORCID, Mario Nonino ORCID, Yolanda Jiménez-Teja ORCID, Masamune Oguri ORCID and other authors.
This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Preprint: archiving forbidden
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Postprint: archiving forbidden
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Data provided by SHERPA/RoMEO

Abstract

Abstract MACS0647–JD is a triply lensed z ∼ 11 galaxy originally discovered with the Hubble Space Telescope. The three lensed images are magnified by factors of ∼8, 5, and 2 to AB mag 25.1, 25.6, and 26.6 at 3.5 μm. The brightest is over a magnitude brighter than other galaxies recently discovered at similar redshifts z > 10 with JWST. Here, we report new JWST imaging that clearly resolves MACS0647–JD as having two components that are either merging galaxies or stellar complexes within a single galaxy. The brighter larger component “A” is intrinsically very blue (β ∼ −2.6 ± 0.1), likely due to very recent star formation and no dust, and is spatially extended with an effective radius ∼70 ± 24 pc. The smaller component “B” (r ∼ 20 − 5 + 8 pc) appears redder (β ∼ −2 ± 0.2), likely because it is older (100–200 Myr) with mild dust extinction (A V ∼ 0.1 mag). With an estimated stellar mass ratio of roughly 2:1 and physical projected separation ∼400 pc, we may be witnessing a galaxy merger 430 million years after the Big Bang. We identify galaxies with similar colors in a high-redshift simulation, finding their star formation histories to be dissimilar, which is also suggested by the spectral energy distribution fitting, suggesting they formed further apart. We also identify a candidate companion galaxy “C” ∼3 kpc away, likely destined to merge with A and B. Upcoming JWST Near Infrared Spectrograph observations planned for 2023 January will deliver spectroscopic redshifts and more physical properties for these tiny magnified distant galaxies observed in the early universe.