Two Massive, Compact, and Dust-obscured Candidate z ≃ 8 Galaxies Discovered by JWST

Hollis B. Akins*, Caitlin M. Casey, Natalie Allen, Micaela B. Bagley, Mark Dickinson, Steven L. Finkelstein, Maximilien Franco, Santosh Harish, Pablo Arrabal Haro, Olivier Ilbert, Jeyhan S. Kartaltepe, Anton M. Koekemoer, Daizhong Liu, Arianna S. Long, Henry Joy McCracken, Louise Paquereau, Casey Papovich, Nor Pirzkal, Jason Rhodes, Brant E. RobertsonMarko Shuntov, Sune Toft, Guang Yang, Guillermo Barro, Laura Bisigello, Véronique Buat, Jaclyn B. Champagne, Olivia Cooper, Luca Costantin, Alexander de la Vega, Nicole E. Drakos, Andreas Faisst, Adriano Fontana, Seiji Fujimoto, Steven Gillman, Carlos Gómez-Guijarro, Ghassem Gozaliasl, Nimish P. Hathi, Christopher C. Hayward, Michaela Hirschmann, Benne W. Holwerda, Shuowen Jin, Dale D. Kocevski, Vasily Kokorev, Erini Lambrides, Ray A. Lucas, Georgios E. Magdis, Benjamin Magnelli, Jed McKinney, Bahram Mobasher

*Corresponding author for this work

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Abstract

We present a search for extremely red, dust-obscured, z > 7 galaxies with JWST/NIRCam+MIRI imaging over the first 20 arcmin2 of publicly available Cycle 1 data from the COSMOS-Web, CEERS, and PRIMER surveys. Based on their red color in F277W−F444W (∼2.5 mag) and detection in MIRI/F770W (∼25 mag), we identify two galaxies, COS-z8M1 and CEERS-z7M1, that have best-fit photometric redshifts of Z= 8.4 +03 -04 and 7.6 +01 -0.1 respectively. We perform spectral energy distribution fitting with a variety of codes (including bagpipes, prospector, beagle, and cigale) and find a >95% probability that these indeed lie at z > 7. Both sources are compact (Reff ≲ 200 pc) and highly obscured (AV ∼ 1.5–2.5) and, at our best-fit redshift estimates, likely have strong [O iii]+Hβ emission contributing to their 4.4 μm photometry. We estimate stellar masses of ∼1010M for both sources; by virtue of detection in MIRI at 7.7 μm, these measurements are robust to the inclusion of bright emission lines, for example, from an active galactic nucleus. We identify a marginal (2.9σ) Atacama Large Millimeter/submillimeter Array detection at 2 mm within 05 of COS-z8M1, which, if real, would suggest a remarkably high IR luminosity of ∼1012L. These two galaxies, if confirmed at z ∼ 8, would be extreme in their stellar and dust masses and may be representative of a substantial population of highly dust-obscured galaxies at cosmic dawn.
Original languageEnglish
Article number61
JournalThe Astrophysical Journal
Volume956
Issue number1
Number of pages17
DOIs
Publication statusPublished - 2023

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