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

Caitlin M. Casey*, Jorge A. Zavala, Manuel Aravena, Matthieu Bethermin, Karina Caputi, Jaclyn B. Champagne, David L. Clements, Elisabete da Cunha, Patrick Drew, Steven L. Finkelstein, Christopher C. Hayward, Jeyhan S. Kartaltepe, Kirsten Knudsen, Anton M. Koekemoer, Georgios E. Magdis, Allison Man, Sinclaire M. Manning, Nick Z. Scoville, Kartik Sheth, Justin SpilkerJohannes Staguhn, Margherita Talia, Yoshiaki Taniguchi, Sune Toft, Ezequiel Treister, Min Yun

*Corresponding author for this work

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We present a physical characterization of MMJ100026.36+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 mu m 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 (CO)-C-12(J = 6 -> 5) and p-H2O (2(1,1) -> 2(0,2)). MAMBO-9 is composed of a pair of galaxies separated by 6 kpc with corresponding star formation rates of 590 M-circle dot yr(-1) and 220 M-circle dot yr(-1), total molecular hydrogen gas mass of (1.7 +/- 0.4) x 10(11) M-circle dot, dust mass of (1.3 +/- 0.3) x 10(9) M-circle dot, and stellar mass of (3.2(-1.5)(+1.0)) x 10(9) M-circle dot. The total halo mass, (3.3 +/- 0.8) x 10(12) M-circle dot, is predicted to exceed 10(15) M-circle dot by z = 0. The system is undergoing a merger-driven starburst that will increase the stellar mass of the system tenfold in tau(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 greater than or similar to 4, the formation of the first massive galaxies, and the formation of interstellar dust at early times (less than or similar to 1 Gyr).

Original languageEnglish
Article number55
Number of pages18
JournalAstrophysical Journal
Issue number1
Publication statusPublished - 10-Dec-2019


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