Two Massive, Compact, and Dust-obscured Candidate z ≃ 8 Galaxies Discovered by JWST
Papovich, Casey; Yang, Guang; Finkelstein, Steven L.; Barro, Guillermo; Buat, Véronique; Pérez-González, Pablo G.; Seillé, Lise-Marie; Arrabal Haro, Pablo; Bagley, Micaela B.; Bisigello, Laura; Casey, Caitlin M.; Costantin, Luca; Dickinson, Mark; Fontana, Adriano; Hathi, Nimish P.; Holwerda, Benne W.; Kartaltepe, Jeyhan S.; Kocevski, Dale D.; Koekemoer, Anton M.; Long, Arianna S.; Lucas, Ray A.; Pirzkal, Nor; Yung, L. Y. Aaron; Fujimoto, Seiji; Mobasher, Bahram; Rhodes, Jason; Ilbert, Olivier; Gillman, Steven; Robertson, Brant E.; McKinney, Jed; Whitaker, Katherine E.; Rich, R. Michael; Toft, Sune; Hirschmann, Michaela; Liu, Daizhong; Faisst, Andreas; Magdis, Georgios E.; Hayward, Christopher C.; Champagne, Jaclyn B.; Urry, C. Megan; Lambrides, Erini; Jin, Shuowen; Kokorev, Vasily; Shuntov, Marko; Valentino, Francesco; Allen, Natalie; Gómez-Guijarro, Carlos; Franco, Maximilien; Drakos, Nicole E.; McCracken, Henry Joy; Akins, Hollis B.; Gozaliasl, Ghassem; Harish, Santosh; Paquereau, Louise; Talia, Margherita; Magnelli, Benjamin; Cooper, Olivia; de La Vega, Alexander; Zavala, Jorge; Cosmos-Web Team; Ceers Team
United States, Denmark, France, Germany, Netherlands, Italy, Spain, Finland, Switzerland, Japan
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 $z={8.4}_{-0.4}^{+0.3}$ and ${7.6}_{-0.1}^{+0.1}$ , 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 (R eff ≲ 200 pc) and highly obscured (A V ~ 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 ~1010 M ⊙ 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 0.″5 of COS-z8M1, which, if real, would suggest a remarkably high IR luminosity of ~1012 L ⊙. 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.