RIOJA. Young Starburst and Ionized Gas Outflows in a $z = 7.212$ Galaxy Uncovered by JWST NIRCam and NIRSpec Observations

Yi W. Ren; Akio K. Inoue; Javier Álvarez-Márquez; Takuya Hashimoto; Luis Colina; Yuma Sugahara; Luca Costantin; Ken Mawatari; Yoshinobu Fudamoto; Santiago Arribas; Alejandro Crespo Gómez; Daniel Ceverino; Yurina Nakazato; Masato Hagimoto; Mitsutaka Usui; Rui Marques-Chaves; Hiroshi Matsuo; Takeshi Hashigaya; Wataru Osone; Carmen Blanco-Prieto; Yoichi Tamura; Naoki Yoshida; Tom J. L. C. Bakx; Miguel Pereira-Santaella

arXiv · 2510.25721

RIOJA. Young Starburst and Ionized Gas Outflows in a $z = 7.212$ Galaxy Uncovered by JWST NIRCam and NIRSpec Observations

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Abstract

We present analysis of JWST NIRCam and NIRSpec observations of the galaxy SXDF-NB1006-2 at $z = 7.212$, as part of the Reionization and the ISM/Stellar Origins with JWST and ALMA (RIOJA) project. We derive the physical properties by conducting spectral energy distribution (SED) fitting, revealing that our target is a young (age $\sim2$ Myr) starburst galaxy with intense radiation field. We detect multiple nebular emission lines from NIRSpec IFS data. We identify a robust broad component of [O III]$\lambda5008$ emission, indicating the presence of ionized gas outflows. The derived gas depletion time of a few hundred Myr implies that our target could be one of the progenitors of massive quiescent galaxies at $z\sim4-5$ identified by recent JWST observations. The spatial distribution of optical and far-infrared (FIR) [O III] emission lines differs in morphology, likely resulting from different critical densities and inhomogeneous density distributions within the galaxy. Potential old stellar populations may be necessary to account for the derived metallicity of $\sim0.2\,\rm{Z}_\odot$, and their presence can be confirmed by future MIRI observations. Including our target, star-forming galaxies at $z>6$ detected by ALMA are generally very young but more massive and brighter in UV than galaxies identified by only JWST. The ALMA-detected galaxies may also have a steeper mass-metallicity relation. These findings suggest that the ALMA-detected galaxies may have experienced more efficient mass assembly processes in their evolutionary pathways.

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Yi W. Ren, Akio K. Inoue, Javier Álvarez-Márquez, Takuya Hashimoto, Luis Colina, Yuma Sugahara, Luca Costantin, Ken Mawatari, Yoshinobu Fudamoto, Santiago Arribas, Alejandro Crespo Gómez, Daniel Ceverino, Yurina Nakazato, Masato Hagimoto, Mitsutaka Usui, Rui Marques-Chaves, Hiroshi Matsuo, Takeshi Hashigaya, Wataru Osone, Carmen Blanco-Prieto, Yoichi Tamura, Naoki Yoshida, Tom J. L. C. Bakx, Miguel Pereira-Santaella. 2025-10-29. RIOJA. Young Starburst and Ionized Gas Outflows in a $z = 7.212$ Galaxy Uncovered by JWST NIRCam and NIRSpec Observations. https://arxiv.org/abs/2510.25721

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