Mapping Obscuration to Reionization with ALMA (MORA): 2 mm Efficiently Selects the Highest-redshift Obscured Galaxies

Caitlin M. Casey, Jorge A. Zavala, Sinclaire M. Manning, Manuel Aravena, Matthieu Bethermin, Karina I. Caputi, Jaclyn B. Champagne, David L. Clements, Patrick Drew, Steven L. Finkelstein, Seiji Fujimoto, Christopher C. Hayward, Anton M. Dekel, Vasily Kokorev, Claudia del P. Lagos, Arianna S. Long, Georgios E. Magdis, Allison W. S. Man, Ikki Mitsuhashi, Gergo PoppingJustin Spilker, Johannes Staguhn, Margherita Talia, Sune Toft, Ezequiel Treister, John R. Weaver, Min Yun

Research output: Contribution to journalArticlepeer-review

39 Citations (Scopus)


We present the characteristics of 2 mm selected sources from the largest Atacama Large Millimeter/submillimeter Array (ALMA) blank-field contiguous survey conducted to date, the Mapping Obscuration to Reionization with ALMA (MORA) survey covering 184 arcmin(2) at 2 mm. Twelve of 13 detections above 5 sigma are attributed to emission from galaxies, 11 of which are dominated by cold dust emission. These sources have a median redshift of < Z(2) (mm)> = 3.6(-0.3)(+0.4) primarily based on optical/near-infrared photometric redshifts with some spectroscopic redshifts, with 77% +/- 11% of sources at z > 3 and 38% +/- 12% of sources at z > 4. This implies that 2 mm selection is an efficient method for identifying the highest-redshift dusty star-forming galaxies (DSFGs). Lower-redshift DSFGs (z < 3) are far more numerous than those at z > 3 yet are likely to drop out at 2 mm. MORA shows that DSFGs with star formation rates in excess of 300 M-circle dot yr(-1) and a relative rarity of similar to 10(-5) Mpc(-3) contribute similar to 30% to the integrated star formation rate density at 3 < z < 6. The volume density of 2 mm selected DSFGs is consistent with predictions from some cosmological simulations and is similar to the volume density of their hypothesized descendants: massive, quiescent galaxies at z > 2. Analysis of MORA sources' spectral energy distributions hint at steeper empirically measured dust emissivity indices than reported in typical literature studies, with = 2.2(-0.4)(+0.5). The MORA survey represents an important step in taking census of obscured star formation in the universe's first few billion years, but larger area 2 mm surveys are needed to more fully characterize this rare population and push to the detection of the universe's first dusty galaxies.

Original languageEnglish
Article number215
Number of pages32
JournalAstrophysical Journal
Issue number2
Publication statusPublished - 20 Dec 2021


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