Dusty Starbursts Masquerading as Ultra-high Redshift Galaxies in JWST CEERS Observations
Authors: Zavala Jorge A. , Buat Véronique , Casey Caitlin M. , Finkelstein Steven L. , Burgarella Denis , Bagley Micaela B. , Ciesla Laure , Daddi Emanuele , Dickinson Mark , Ferguson Henry C. , Franco Maximilien , Jiménez-Andrade E. F. , Kartaltepe Jeyhan S. , Koekemoer Anton M. , Le Bail Aurélien , Murphy E. J. , Papovich Casey , Tacchella Sandro , Wilkins Stephen M. , Aretxaga Itziar , Behroozi Peter , Champagne Jaclyn B. , Fontana Adriano , Giavalisco Mauro , Grazian Andrea , Grogin Norman A. , Kewley Lisa J. , Kocevski Dale D. , Kirkpatrick Allison , Lotz Jennifer M. , Pentericci Laura , Pérez-González Pablo G. , Pirzkal Nor , Ravindranath Swara , Somerville Rachel S. , Trump Jonathan R. , Yang Guang , Yung L. Y. Aaron , Almaini Omar , Amorín Ricardo O. , Annunziatella Marianna , Arrabal Haro Pablo , Backhaus Bren E. , Barro Guillermo , Bell Eric F. , Bhatawdekar Rachana , Bisigello Laura , Buitrago Fernando , Calabrò Antonello , Castellano Marco , Chávez Ortiz Óscar A. , Chworowsky Katherine , Cleri Nikko J. , Cohen Seth H. , Cole Justin W. , Cooke Kevin C. , Cooper M. C. , Cooray Asantha R. , Costantin Luca , Cox Isabella G. , Croton Darren , Davé Romeel , de la Vega Alexander , Dekel Avishai , Elbaz David , Estrada-Carpenter Vicente , Fernández Vital , Finkelstein Keely D. , Freundlich Jonathan , Fujimoto Seiji , García-Argumánez Ángela , Gardner Jonathan P. , Gawiser Eric , Gómez-Guijarro Carlos , Guo Yuchen , Hamilton Timothy S. , Hathi Nimish P. , Holwerda Benne W. , Hirschmann Michaela , Huertas-Company Marc , Hutchison Taylor A. , Iyer Kartheik G. , Jaskot Anne E. , Jha Saurabh W. , Jogee Shardha , Juneau Stéphanie , Jung Intae , Kassin Susan A. , Kurczynski Peter , Larson Rebecca L. , Leung Gene C. K. , Long Arianna S. , Lucas Ray A. , Magnelli Benjamin , Mantha Kameswara Bharadwaj , Matharu Jasleen , McGrath Elizabeth J. , McIntosh Daniel H. , Medrano Aubrey , Merlin Emiliano , Mobasher Bahram , Morales Alexa M. , Newman Jeffrey A. , Nicholls David C. , Pandya Viraj , Rafelski Marc , Ronayne Kaila , Rose Caitlin , Ryan Russell E. , Santini Paola , Seillé Lise-Marie , Shah Ekta A. , Shen Lu , Simons Raymond C. , Snyder Gregory F. , Stanway Elizabeth R. , Straughn Amber N. , Teplitz Harry I. , Vanderhoof Brittany N. , Vega-Ferrero Jesús , Wang Weichen , Weiner Benjamin J. , Willmer Christopher N. A. , Wuyts Stijn ,   (The CEERS Team)
Published: January 2023

Lyman-break galaxy (LBG) candidates at z ≳ 10 are rapidly being identified in James Webb Space Telescope (JWST)/NIRCam observations. Due to the (redshifted) break produced by neutral hydrogen absorption of rest-frame UV photons, these sources are expected to drop out in the bluer filters while being well detected in redder filters. However, here we show that dust-enshrouded star-forming galaxies at lower redshifts (z ≲ 7) may also mimic the near-infrared (near-IR) colors of z > 10 LBGs, representing potential contaminants in LBG candidate samples. First, we analyze CEERS-DSFG-1, a NIRCam dropout undetected in the F115W and F150W filters but detected at longer wavelengths. Combining the JWST data with (sub)millimeter constraints, including deep NOEMA interferometric observations, we show that this source is a dusty star-forming galaxy (DSFG) at z ≈ 5.1. We also present a tentative 2.6σ SCUBA-2 detection at 850 μm around a recently identified z ≈ 16 LBG candidate in the same field and show that, if the emission is real and associated with this candidate, the available photometry is consistent with a z ∼ 5 dusty galaxy with strong nebular emission lines despite its blue near-IR colors. Further observations on this candidate are imperative to mitigate the low confidence of this tentative submillimeter emission and its positional uncertainty. Our analysis shows that robust (sub)millimeter detections of NIRCam dropout galaxies likely imply z ∼ 4–6 redshift solutions, where the observed near-IR break would be the result of a strong rest-frame optical Balmer break combined with high dust attenuation and strong nebular line emission, rather than the rest-frame UV Lyman break. This provides evidence that DSFGs may contaminate searches for ultra-high redshift LBG candidates from JWST observations.