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

Tiger Yu Yang Hsiao, Dan Coe, Abdurro’uf, Lily Whitler, Intae Jung, Gourav Khullar, Ashish Kumar Meena, Pratika Dayal, Kirk S.S. Barrow, Lillian Santos-Olmsted, Adam Casselman, Eros Vanzella, Mario Nonino, Yolanda Jiménez-Teja, Masamune Oguri, Daniel P. Stark, Lukas J. Furtak, Adi Zitrin, Angela Adamo, Gabriel BrammerLarry Bradley, Jose M. Diego, Erik Zackrisson, Steven L. Finkelstein, Rogier A. Windhorst, Rachana Bhatawdekar, Taylor A. Hutchison, Tom Broadhurst, Paola Dimauro, Felipe Andrade-Santos, Jan J. Eldridge, Ana Acebron, Roberto J. Avila, Matthew B. Bayliss, Alex Benítez, Christian Binggeli, Patricia Bolan, Maruša Bradač, Adam C. Carnall, Christopher J. Conselice, Megan Donahue, Brenda Frye, Seiji Fujimoto, Alaina Henry, Bethan L. James, Susan A. Kassin, Lisa Kewley, Rebecca L. Larson, Tod Lauer, David Law, Guillaume Mahler, Ramesh Mainali, Stephan McCandliss, David Nicholls, Norbert Pirzkal, Marc Postman, Jane R. Rigby, Russell Ryan, Peter Senchyna, Keren Sharon, Ikko Shimizu, Victoria Strait, Mengtao Tang, Michele Trenti, Anton Vikaeus, Brian Welch

Research output: Contribution to journalArticlepeer-review

12 Scopus citations


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.

Original languageEnglish (US)
Article numberL34
JournalAstrophysical Journal Letters
Issue number2
StatePublished - Jun 1 2023

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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