JWST reveals a possible $z \sim 11$ galaxy merger in triply-lensed MACS0647$-$JD
Creators: name: Hsiao, Tiger Yu-Yang
name: Coe, Dan
name: Abdurro'uf
name: Whitler, Lily
name: Jung, Intae
name: Khullar, Gourav
name: Meena, Ashish Kumar
name: Dayal, Pratika
name: Barrow, Kirk S. S.
name: Santos-Olmsted, Lillian
name: Casselman, Adam
name: Vanzella, Eros
name: Nonino, Mario
name: Jimenez-Teja, Yolanda
name: Oguri, Masamune
name: Stark, Daniel P.
name: Furtak, Lukas J.
name: Zitrin, Adi
name: Adamo, Angela
name: Brammer, Gabriel
name: Bradley, Larry
name: Diego, Jose M.
name: Zackrisson, Erik
name: Finkelstein, Steven L.
name: Windhorst, Rogier A.
name: Bhatawdekar, Rachana
name: Hutchison, Taylor A.
name: Broadhurst, Tom
name: Dimauro, Paola
name: Andrade-Santos, Felipe
name: Eldridge, Jan J.
name: Acebron, Ana
name: Avila, Roberto J.
name: Bayliss, Matthew B.
name: Benitez, Alex
name: Binggeli, Christian
name: Bolan, Patricia
name: Bradac, Marusa
name: Carnall, Adam C.
name: Conselice, Christopher J.
name: Donahue, Megan
name: Frye, Brenda
name: Fujimoto, Seiji
name: Henry, Alaina
name: James, Bethan L.
name: Kassin, Susan
name: Kewley, Lisa
name: Larson, Rebecca L.
name: Lauer, Tod
name: Law, David
name: Mahler, Guillaume
name: Mainali, Ramesh
name: McCandliss, Stephan
name: Nicholls, David
name: Pirzkal, Norbert
name: Postman, Marc
name: Rigby, Jane R.
name: Ryan, Russell
name: Senchyna, Peter
name: Sharon, Keren
name: Shimizu, Ikko
name: Strait, Victoria
name: Tang, Mengtao
name: Trenti, Michele
name: Vikaeus, Anton
name: Welch, Brian
Publisher: name: arXiv
Year: 2022
Subjects: subject: Astrophysics of Galaxies (astro-ph.GA)
subject: Cosmology and Nongalactic Astrophysics (astro-ph.CO)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: MACS0647$-$JD is a triply-lensed $z\sim11$ galaxy originally discovered with the Hubble Space Telescope. Here we report new JWST imaging, which clearly resolves MACS0647$-$JD as having two components that are either merging galaxies or stellar complexes within a single galaxy. Both are very small, with stellar masses $\sim10^8\,M_\odot$ and radii $r&lt;100\,\rm pc$. The brighter larger component "A" is intrinsically very blue ($β\sim-2.6$), likely due to very recent star formation and no dust, and is spatially extended with an effective radius $\sim70\,\rm pc$. The smaller component "B" appears redder ($β\sim-2$), likely because it is older ($100-200\,\rm Myr$) with mild dust extinction ($A_V\sim0.1\,\rm mag$), and a smaller radius $\sim20\,\rm pc$. We identify galaxies with similar colors in a high-redshift simulation, finding their star formation histories to be out of phase. With an estimated stellar mass ratio of roughly 2:1 and physical projected separation $\sim400\,\rm pc$, we may be witnessing a galaxy merger 400 million years after the Big Bang. We also identify a candidate companion galaxy C $\sim3\,{\rm kpc}$ away, likely destined to merge with galaxies A and B. The combined light from galaxies A+B is magnified by factors of $\sim$8, 5, and 2 in three lensed images JD1, 2, and 3 with F356W fluxes $\sim322$, $203$, $86\,\rm nJy$ (AB mag 25.1, 25.6, 26.6). MACS0647$-$JD is significantly brighter than other galaxies recently discovered at similar redshifts with JWST. Without magnification, it would have AB mag 27.3 ($M_{UV}=-20.4$). With a high confidence level, we obtain a photometric redshift of $z=10.6\pm0.3$ based on photometry measured in 6 NIRCam filters spanning $1-5\rmμm$, out to $4300\,Å$ rest-frame. JWST NIRSpec observations planned for January 2023 will deliver a spectroscopic redshift and a more detailed study of the physical properties of MACS0647$-$JD.
description: 27 pages, 14 figures, accepted for publication in ApJL