RIOJA. A Clumpy Galaxy Assembly at Redshift 6.81 Revealed by JWST
Journal article, 2026
Spatially resolved multiwavelength analysis is essential to study galaxy formation and evolution. A UV-bright galaxy COS-2987030247 at z = 6.81 is one of the Rosetta Stones in the epoch of reionization for which JWST NIRSpec Integral Field Spectroscopy, NIRCam imaging, and Atacama Large Millimeter/submillimeter Array data are available thanks to the RIOJA program. We identified the rest-frame optical emission lines from the ionized hydrogen, oxygen, and neon gas. The [O iii] 5008 & Aring; line emission and the NIRCam images show a complex kinematical and morphological structure where two bright main and three faint clumps are identified in a 10 kpc extent. The system is not classified as a purely rotation-dominated disk. The multiple clumps are instead consistent with a merger-related origin, including either distinct galaxies in interaction or star-forming clumps formed through tidal gas compression during a merger. The spatially resolved emission line fluxes show that dust attenuation, metal enrichment, and ionization parameter are preferentially enhanced in the star formation peaks. Our spectral energy distribution fitting suggests that the main clumps are in a moderately dust-attenuated star-forming phase (AV = 0.2-0.3 and SFR(H alpha) similar to 10 M circle dot yr-1) with almost zero escape fraction of ionizing photons. In contrast, the subclumps are dust-free and lying on or below the main sequence of star-forming galaxies. These subclumps may work as a perturber that triggers the clumpy starburst in the surrounding gas through the merger event.
Author
Ken Mawatari
University of Tsukuba
Waseda University
Luca Costantin
Spanish National Research Council (CSIC)
Mitsutaka Usui
University of Tsukuba
Takuya Hashimoto
University of Tsukuba
Javier Alvarez-Marquez
Spanish National Research Council (CSIC)
Yuma Sugahara
Waseda University
Luis Colina
Spanish National Research Council (CSIC)
Akio K. Inoue
Waseda University
Wataru Osone
University of Tsukuba
Santiago Arribas
Spanish National Research Council (CSIC)
Rui Marques-Chaves
University of Geneva
Yurina Nakazato
University of Tokyo
Flatiron Institute
Masato Hagimoto
Nagoya University
Takeshi Hashigaya
Kyoto University
Daniel Ceverino
Universidad Autonoma de Madrid (UAM)
Naoki Yoshida
University of Tokyo
Tom Bakx
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Yoshinobu Fudamoto
Chiba University
Alejandro Crespo Gomez
Space Telescope Science Institute (STScI)
Hiroshi Matsuo
National Astronomical Observatory of Japan
The Graduate University for Advanced Studies (SOKENDAI)
Miguel Pereira-Santaella
Spanish National Research Council (CSIC)
Carmen Blanco-Prieto
Spanish National Research Council (CSIC)
Yi W. Ren
Waseda University
Yoichi Tamura
Nagoya University
Astrophysical Journal
0004-637X (ISSN) 1538-4357 (eISSN)
Vol. 998 1 119Subject Categories (SSIF 2025)
Astronomy, Astrophysics, and Cosmology
DOI
10.3847/1538-4357/ae3151