A Near-infrared-faint, Far-infrared-luminous Dusty Galaxy at z 5 in COSMOS-Web

October 2023 • 2023ApJ...956...72M

Authors • McKinney, Jed • Manning, Sinclaire M. • Cooper, Olivia R. • Long, Arianna S. • Akins, Hollis • Casey, Caitlin M. • Faisst, Andreas L. • Franco, Maximilien • Hayward, Christopher C. • Lambrides, Erini • Magdis, Georgios • Whitaker, Katherine E. • Yun, Min • Champagne, Jaclyn B. • Drakos, Nicole E. • Gentile, Fabrizio • Gillman, Steven • Gozaliasl, Ghassem • Ilbert, Olivier • Jin, Shuowen • Koekemoer, Anton M. • Kokorev, Vasily • Liu, Daizhong • Rich, R. Michael • Robertson, Brant E. • Valentino, Francesco • Weaver, John R. • Zavala, Jorge A. • Allen, Natalie • Kartaltepe, Jeyhan S. • McCracken, Henry Joy • Paquereau, Louise • Rhodes, Jason • Shuntov, Marko • Toft, Sune

Abstract • A growing number of far-infrared (FIR) bright sources completely invisible in deep extragalactic optical surveys hint at an elusive population of z > 4 dusty, star-forming galaxies. Cycle 1 JWST surveys are now detecting their rest-frame optical light, which provides key insight into their stellar properties and statistical constraints on the population as a whole. This work presents the JWST Near Infrared Camera (NIRCam) counterpart from the COSMOS-Web survey to an FIR SCUBA-2 and Atacama Large Millimeter/submillimeter Array (ALMA) source, AzTECC71, which was previously undetected at wavelengths shorter than 850 μm. AzTECC71, among the reddest galaxies in COSMOS-Web with F277W - F444W ~ 0.9, is undetected in NIRCam/F150W and F115W and fainter in F444W than other submillimeter galaxies identified in COSMOS-Web by 2-4 magnitudes. This is consistent with the system having both a lower stellar mass and higher redshift than the median dusty, star-forming galaxy. With deep ground- and space-based upper limits combined with detections in F277W, F444W, and the FIR including ALMA Band 6, we find a high probability (99%) that AzTECC71 is at z > 4 with ${z}_{\mathrm{phot}}={5.7}_{-0.7}^{+0.8}$ . This galaxy is massive ( $\mathrm{log}\,{M}_{* }/{M}_{\odot }\sim 10.7$ ) and infrared-luminous ( $\mathrm{log}\,{L}_{\mathrm{IR}}/{L}_{\odot }\sim 12.7$ ), comparable to other optically undetected but FIR-bright dusty, star-forming galaxies at z > 4. This population of luminous, infrared galaxies at z > 4 is largely unconstrained but comprises an important bridge between the most extreme dust-obscured galaxies and more typical high-redshift star-forming galaxies. If further FIR-selected galaxies that drop out of the F150W filter in COSMOS-Web have redshifts z > 4 like AzTECC71, then the volume density of such sources may be ~3-10 × greater than previously estimated.

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Andreas Faisst

Assistant Scientist