The Extended Mapping Obscuration to Reionization with ALMA (Ex-MORA) Survey: 5σ Source Catalog and Redshift Distribution
Journal article, 2026
One of the greatest challenges in galaxy evolution over the last decade has been constraining the prevalence of heavily dust-obscured galaxies in the early Universe. At z > 3, these galaxies are increasingly rare, and difficult to identify, as they are interspersed among the more numerous dust-obscured galaxy population at z = 1-3, making efforts to secure confident spectroscopic redshifts expensive, and sometimes unsuccessful. In this work, we present the Extended Mapping Obscuration to Reionization with the Atacama Large Millimeter/submillimeter Array (ALMA; Ex-MORA) Survey-a 2 mm blank-field survey in the COSMOS-Web field, and the largest ever ALMA blank-field survey to date, covering 577 arcmin(2). Ex-MORA is an expansion of the MORA survey designed to identify primarily z > 3 dusty, star-forming galaxies while simultaneously filtering out the more numerous z < 3 population by leveraging the very negative K-correction at observed-frame 2 mm. We identify 37 significant (>5 sigma) sources, 33 of which are robust thermal dust emitters. We measure a median redshift of < z >=3.8(-1.52)(+1.7), with two-thirds of the sample at z > 3, and just under half at z > 4, demonstrating the overall success of the 2 mm selection technique. The total integrated z > 3 volume density of Ex-MORA sources is similar to 1-3 & times; 10(-5) Mpc(-3), consistent with other surveys of infrared luminous galaxies at similar epochs. We also find that techniques using rest-frame optical emission (or lack thereof) to identify z > 3 heavily dust-obscured galaxies miss at least half of Ex-MORA galaxies. This supports the idea that the dusty galaxy population is heterogeneous, and that synergies across observatories spanning multiple energy regimes are critical to understanding their formation and evolution at z > 3.
Author
Arianna S. Long
University of Washington
University of Texas
Caitlin M. Casey
University of Texas
Jed McKinney
University of Texas
Jorge A. Zavala
National Astronomical Observatory of Japan
Hollis B. Akins
University of Texas
Olivia R. Cooper
University of Texas
Erini L. Lambrides
National Aeronautics and Space Administration (NASA)
Maximilien Franco
Paris Cité University
Manuel Aravena
Diego Portales University
Matthieu Bethermin
Aix Marseille University
University of Strasbourg
Karina Caputi
University of Groningen
Jaclyn B. Champagne
University of Arizona
D. L. Clements
Imperial College London
Elisabete Da Cunha
University of Western Australia
Andreas L. Faisst
California Institute of Technology (Caltech)
Fabrizio Gentile
Istituto nazionale di astrofisica (INAF)
Paris Cité University
Jacqueline Hodge
Leiden University
Allison W. S. Man
University of British Columbia (UBC)
Sinclaire M. Manning
University of Massachusetts
David B. Sanders
University of Hawaii
Margherita Talia
Istituto nazionale di astrofisica (INAF)
University of Bologna
Ezequiel Treister
Universidad de Tarapacá
Gabriel Brammer
University of Copenhagen
Marcella Brusa
University of Bologna
Steven L. Finkelstein
University of Texas
Seiji Fujimoto
University of Texas
Christopher C. Hayward
Flatiron Institute
Olivier Ilbert
Aix Marseille University
Jean-Baptiste Jolly
Max Planck Society
Jeyhan S. Kartaltepe
Rochester Institute of Technology
Kirsten Knudsen
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Anton M. Koekemoer
Space Telescope Science Institute (STScI)
Daizhong Liu
Chinese Academy of Sciences
Georgios Magdis
Technical University of Denmark (DTU)
University of Copenhagen
Henry Joy McCracken
Inst Astrophys Paris
Sorbonne University
Jason Rhodes
California Institute of Technology (Caltech)
Brant E. Robertson
University of California
Nick Scoville
California Institute of Technology (Caltech)
Kartik Sheth
National Aeronautics and Space Administration (NASA)
Vernesa Smolcic
University of Zagreb
Justin Spilker
Texas A&M University
Yoshiaki Taniguchi
The Open University of Japan
Sune Toft
University of Copenhagen
C. Megan Urry
Yale University
Min Yun
University of Massachusetts
Astrophysical Journal
0004-637X (ISSN) 1538-4357 (eISSN)
Vol. 999 1 47Subject Categories (SSIF 2025)
Astronomy, Astrophysics, and Cosmology
DOI
10.3847/1538-4357/ae2fda