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, O. Ilbert, Jeyhan S. Kartaltepe, Anton M. Koekemoer, Daizhong Liu, Arianna S. Long, H. J. McCracken, Louise Paquereau, Casey Papovich, Nor Pirzkal, Jason Rhodes, Brant Robertson, Marko Shuntov, Sune Toft, Guang Yang, Guillermo Barro, Laura Bisigello, V. Buat, Jaclyn B. Champagne, Olivia R. Cooper, Luca Costantin, Alexander de la Vega, Nicole E. Drakos, Andreas L. Faisst, A. Fontana, Seiji Fujimoto, Steven Gillman, Carlos Gómez-Guijarro, G. Gozaliasl, Nimish P. Hathi, Christopher C. Hayward, Michaela Hirschmann, Benne W. Holwerda, Shuowen Jin, Dale D. Kocevski, Vasily Kokorev, Erini Lambrides, Ray A. Lucas, G. Magdis, B. Magnelli, Jed McKinney, Bahram Mobasher, Pablo G. Pérez‐González, R. Michael Rich, Lise-Marie Seillé, M. Talia, C. M. Urry, Francesco Valentino, Katherine E. Whitaker, L. Y. Aaron Yung, Jorge A. Zavala, the COSMOS-Web and CEERS teams
Abstract
Abstract We present a search for extremely red, dust-obscured, z > 7 galaxies with JWST/NIRCam+MIRI imaging over the first 20 arcmin 2 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>z</mml:mi> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>8.4</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.4</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.3</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>7.6</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.1</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.1</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> , 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 ]+H β emission contributing to their 4.4 μ m photometry. We estimate stellar masses of ∼10 10 M ⊙ for both sources; by virtue of detection in MIRI at 7.7 μ m, these measurements are robust to the inclusion of bright emission lines, for example, from an active galactic nucleus. We identify a marginal (2.9 σ ) 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 ∼10 12 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.