ALMA FIR View of Ultra-high-redshift Galaxy Candidates at z ∼ 11-17: Blue Monsters or Low-z Red Interlopers?

Seiji Fujimoto, Steven L. Finkelstein, Denis Burgarella, Chris L. Carilli, Véronique Buat, Caitlin M. Casey, Laure Ciesla, Sandro Tacchella, Jorge A. Zavala, Gabriel Brammer, Yoshinobu Fudamoto, Masami Ouchi, Francesco Valentino, M. C. Cooper, Mark Dickinson, Maximilien Franco, Mauro Giavalisco, Taylor A. Hutchison, Jeyhan S. Kartaltepe, Anton M. KoekemoerTakashi Kojima, Rebecca L. Larson, E. J. Murphy, Casey Papovich, Pablo G. Pérez-González, Rachel S. Somerville, Ilsang Yoon, Stephen M. Wilkins, Hollis Akins, Ricardo O. Amorín, Pablo Arrabal Haro, Micaela B. Bagley, Katherine Chworowsky, Nikko J. Cleri, Olivia R. Cooper, Luca Costantin, Emanuele Daddi, Henry C. Ferguson, Norman A. Grogin, E. F. Jiménez-Andrade, Stéphanie Juneau, Allison Kirkpatrick, Dale D. Kocevski, Aurélien Le Bail, Arianna Long, Ray A. Lucas, Benjamin Magnelli, Jed McKinney, Caitlin Rose, Lise Marie Seillé, Raymond C. Simons, Benjamin J. Weiner, L. Y.Aaron Yung

Research output: Contribution to journalArticlepeer-review

5 Scopus citations


We present Atacama Large Millimeter/submillimeter Array (ALMA) Band 7 observations of a remarkably bright galaxy candidate at z phot = 16.7 − 0.3 + 1.9 (M UV = −21.6), S5-z17-1, identified in James Webb Space Telescope (JWST) Early Release Observation data of Stephen’s Quintet. We do not detect the dust continuum at 866 μm, ruling out the possibility that S5-z17-1 is a low-z dusty starburst with a star formation rate of ≳30 M yr−1. We detect a 5.1σ line feature at 338.726 ± 0.007 GHz exactly coinciding with the JWST source position, with a 2% likelihood of the signal being spurious. The most likely line identification would be [O iii]52 μm at z = 16.01 or [C ii]158 μm at z = 4.61, whose line luminosities do not violate the nondetection of the dust continuum in both cases. Together with three other z ≳ 11-13 candidate galaxies recently observed with ALMA, we conduct a joint ALMA and JWST spectral energy distribution (SED) analysis and find that the high-z solution at z ∼ 11-17 is favored in every candidate as a very blue (UV continuum slope of ≃−2.3) and luminous (M UV ≃ [ − 24:−21]) system. Still, we find in several candidates that reasonable SED fits (Δχ 2 ≲ 4) are reproduced by type II quasar and/or quiescent galaxy templates with strong emission lines at z ∼ 3-5, where such populations predicted from their luminosity functions and EW([O iii]+Hβ) distributions are abundant in survey volumes used for the identification of the z ∼ 11-17 candidates. While these recent ALMA observation results have strengthened the likelihood of the high-z solutions, lower-z possibilities are not completely ruled out in several of the z ∼ 11-17 candidates, indicating the need to consider the relative surface densities of the lower-z contaminants in the ultra-high-z galaxy search.

Original languageEnglish (US)
Article number130
JournalAstrophysical Journal
Issue number2
StatePublished - Oct 1 2023

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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