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. Koekemoer, Takashi Kojima, Rebecca L. Larson, Eric J. Murphy, Casey Papovich, Pablo G. Pérez-González, Rachel S. Somerville, Ilsang Yoon, Stephen M. Wilkins, L. Y. Aaron Yung, Hollis Akins, Ricardo O. Amorín, Pablo Arrabal Haro, Micaela B. Bagley, Katherine Chworowsky, 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

Submitted on 7 November 2022, last revised on 12 November 2022


We present ALMA Band 7 observations of a remarkably bright galaxy candidate at zphot=16.70.3+1.9 (MUV=21.6), S5-z17-1, identified in 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 (SFR) of 30M yr1. 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 [OIII]52μm at z=16.01 or [CII]158μm at z=4.61, whose line luminosities do not violate the non-detection 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 z11-17 is favored in every candidate as a very blue (UV continuum slope of 2.3) and luminous (MUV [24:21]) system. Still, we find in some candidates that reasonable SED fits (Δ χ24) are reproduced by type-II quasar and/or quiescent galaxy templates with strong emission lines at -5, where such populations predicted from their luminosity functions and EW([OIII]+H) distributions are abundant in survey volumes used for the 11-17 candidates. While these recent ALMA observation results have strengthened the likelihood of the high- solutions, lower- possibilities are not completely ruled out in some of the 11-17 candidates.


Comment: 23 pages, 8 figures, 7 tables, submitted to ApJ. A typo in Table4 is corrected

Subjects: Astrophysics - Astrophysics of Galaxies; Astrophysics - Cosmology and Nongalactic Astrophysics


{\it Left:} The NIR SED of \targb. The red circles and arrows indicate the observed flux densities and 2$\sigma$ upper limits, respectively. The blue and green curves and redshift labels represent the best-fit model SEDs and photometric redshifts by {\sc cigale} with the redshift range at $0<z<25$ and $0<z<10$, respectively. The blue and green open circles are predicted flux densities in the NIRCam filters based on the best-fit SEDs. The low-$z$ forced SED has a brighter submm flux by $>100$ times than the best-fit high-$z$ SED, expecting a $\sim10\sigma$ detection from the ALMA Band~7 observation (grey curve in Figure \ref{fig:nircam_alma}). The images on this panel present $2''\times2''$ NIRCam cutout images of \targb. {\it Middle:} $P(z)$ from the SED fitting by {\sc eazy} (brown curve) and {\sc cigale} (light blue curve) with a redshift range at $0 < z< 25$. {\it Right:} Same as the middle panel, but at $0 < z< 10$. The grey dashed line denotes the atmospheric transmission for \cii. The red shade indicates the \cii\ redshift range of $z=4.31$--4.69 covered by our ALMA Band~7 observations spanning 334--358~GHz with 3 frequency tunings, which is optimized to maximally cover the peak of the lower-redshift solution's $P(z)$ and avoid the significantly low atmospheric transmission.