Physical Characterization of an Unlensed, Dusty Star-forming Galaxy at z = 5.85
Journal article, 2019

We present a physical characterization of MM J100026.36+021527.9 (a.k.a. "Mambo-9"), a dusty star-forming galaxy (DSFG) at z = 5.850 ± 0.001. This is the highest-redshift unlensed DSFG (and fourth most distant overall) found to date and is the first source identified in a new 2 mm blank-field map in the COSMOS field. Though identified in prior samples of DSFGs at 850 μm to 1.2 mm with unknown redshift, the detection at 2 mm prompted further follow-up as it indicated a much higher probability that the source was likely to sit at z > 4. Deep observations from the Atacama Large Millimeter and submillimeter Array (ALMA) presented here confirm the redshift through the secure detection of 12CO(J = 6→5) and p-H2O (21,1 → 20,2). Mambo-9 is composed of a pair of galaxies separated by 6 kpc with corresponding star formation rates of 590 M o˙ yr-1 and 220 M o˙ yr-1, total molecular hydrogen gas mass of (1.7 ± 0.4) × 1011 M o˙, dust mass of (1.3 ± 0.3) × 109 M o˙, and stellar mass of (3.2-1.5+1.0) × 109 M o˙. The total halo mass, (3.3 ± 0.8) × 1012 M o˙, is predicted to exceed 1015 M o˙ by z = 0. The system is undergoing a merger-driven starburst that will increase the stellar mass of the system tenfold in τ depl = 40-80 Myr, converting its large molecular gas reservoir (gas fraction of 96-2+1) into stars. Mambo-9 evaded firm spectroscopic identification for a decade, following a pattern that has emerged for some of the highest-redshift DSFGs found. And yet, the systematic identification of unlensed DSFGs like Mambo-9 is key to measuring the global contribution of obscured star formation to the star formation rate density at z ⪆ 4, the formation of the first massive galaxies, and the formation of interstellar dust at early times (≲1 Gyr).


Caitlin M. Casey

The University of Texas at Austin

J. A. Zavala

The University of Texas at Austin

Manuel Aravena

Diego Portales University

Matthieu Béthermin

Laboratoire d'Astrophysique de Marseille

Karina I. Caputi

University of Copenhagen

University of Groningen

Jaclyn B. Champagne

The University of Texas at Austin

D. L. Clements

Imperial College London

E. Da Cunha

University of Western Australia

ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D)

Australian National University

Patrick Drew

The University of Texas at Austin

Steven L. Finkelstein

The University of Texas at Austin

Christopher C. Hayward

Flatiron Institute

Jeyhan S. Kartaltepe

Rochester Institute of Technology

Kirsten Kraiberg Knudsen

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics, Extragalactic Astrophysics

Anton M. Koekemoer

Space Telescope Science Institute (STScI)

Georgios E. Magdis

University of Copenhagen

Niels Bohr Institute

Allison Man

University of Toronto

Sinclaire M. Manning

The University of Texas at Austin

N. Z. Scoville

California Institute of Technology (Caltech)

K. Sheth

National Aeronautics and Space Administration

Justin Spilker

The University of Texas at Austin

Johannes Staguhn

NASA Goddard Space Flight Center

Johns Hopkins University

Margherita Talia

University of Bologna

Yoshiaki Taniguchi

The Open University of Japan

Sune Toft

University of Copenhagen

Niels Bohr Institute

E. Treister

Pontificia Universidad Catolica de Chile

Min Yun

University of Massachusetts

Astrophysical Journal

0004-637X (ISSN) 1538-4357 (eISSN)

Vol. 887 1 55

Subject Categories

Analytical Chemistry

Astronomy, Astrophysics and Cosmology

Chemical Process Engineering



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