JWST+ALMA Reveal the Interstellar Medium Kinematics and Stellar Structure of MAMBO-9, a Merging Pair of DSFGs in an Overdense Environment at z = 5.85
Journal article, 2026
We present high-resolution Atacama Large Millimeter/submillimeter Array (ALMA) [C ii] 158 μm observations and JWST/NIRCam+MIRI imaging of MAMBO-9, a pair of optically dark, dusty star-forming galaxies at z = 5.85. MAMBO-9 is among the most massive, gas-rich, and actively star-forming galaxies at this epoch, when the Universe was less than 1 Gyr old. The new 400 pc resolution [C ii] observations reveal velocity gradients in both objects; we estimate the dynamical masses and find a relative mass ratio of 1:5. The kinematics of both objects suggest both rotation and strong tidal interaction, suggesting that the pair has already experienced a close encounter. Indeed, the new JWST imaging reveals a continuous bridge of moderately dust-obscured material between the two. We perform spatially resolved spectral energy distribution (SED) fitting using the high-resolution ALMA+JWST imaging, finding that the majority of the recent star formation is concentrated in extremely obscured (AV > 10) clouds, while the majority of the rest-optical light (stellar continuum and Hα emission) is emergent from moderately to highly obscured (AV ∼ 1–5) regions on the outskirts. Combining our new stellar and dynamical mass measurements with previous CO observations, we find that the mass budget of MAMBO-9 requires a CO-to-H2 conversion factor (αCO) of order unity (∼1–2), indicative of a highly metal-enriched interstellar medium. Finally, we show that MAMBO-9 resides in a large overdensity spanning the PRIMER-COSMOS field, with 39 galaxies spectroscopically confirmed within ∼25 cMpc. With a total baryonic mass of ∼1011 M⊙, MAMBO-9 can be considered a prototype of massive galaxy formation and a likely progenitor of the brightest cluster galaxies in the lower-redshift Universe.
Galaxy evolution (594)
Circumgalactic medium (1879)
High-redshift galaxies (734)
Interstellar medium (847)
Galaxy formation (595)
Author
Hollis B. Akins
University of Texas
Caitlin M. Casey
University of California
University of Texas
Cosmic Dawn Center (DAWN)
Jaclyn B. Champagne
University of Arizona
Olivia Cooper
University of Colorado
M. Franco
University Paris-Saclay
S. Fujimoto
University of Toronto
University of Texas
Kirsten Knudsen
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Anton M. Koekemoer
Space Telescope Science Institute (STScI)
Arianna S. Long
University of Washington
Allison Man
University of British Columbia (UBC)
Sinclaire M. Manning
University of Massachusetts
Jed McKinney
University of Texas
J. A. Zavala
University of Massachusetts
Pablo Arrabal Haro
National Aeronautics and Space Administration (NASA)
Mark Dickinson
NSF's National Optical-Infrared Astronomy Research Laboratory (NOIRLab)
V. Kokorev
University of Texas
Anthony J. Taylor
University of Texas
Astrophysical Journal
0004-637X (ISSN) 1538-4357 (eISSN)
Vol. 1006 2 229Subject Categories (SSIF 2025)
Atom and Molecular Physics and Optics
Astronomy, Astrophysics, and Cosmology
DOI
10.3847/1538-4357/ae8449