Spatially resolved metallicity and ionization in the merging system Gz9p3 at z=9.3

Arjan Bik; Javier Álvarez-Márquez; Alejandro Crespo Gómez; Luis Colina; Pablo G. Pérez-González; Göran Östlin; Carmen Blanco Prieto; Jens Melinder; Danial Langeroodi; Gillian Wright; Hiddo S. B. Algera; Leindert A. Boogaard; Karina Caputi; Steven Gillman; Thomas Greve; Jens Hjorth; Edoardo Iani; Sarah Kendrew; Alvaro Labiano Ortega; Michele Perna; Carlota Prieto Jimenez; John Pye; Pierluigi Rinaldi; Paul van der Werf; Fabian Walter; Florian Peißker; Andreas Eckart; Thomas Henning; Manuel Güdel

arXiv · 2604.22460

Spatially resolved metallicity and ionization in the merging system Gz9p3 at z=9.3

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Abstract

Studying the interstellar medium (ISM) in merging high-redshift galaxies is crucial for understanding early galaxy assembly, star formation, and black hole growth, predicted by hierarchical $\Lambda$CDM models. Deep imaging and spatially resolved spectroscopy with JWST enable unprecedented insight into these processes, even for galaxies in the Epoch of Reionization. We present NIRSpec and MIRI integral field spectroscopy and MIRI imaging of the merging galaxy Gz9p3 at z=9.3 of the UV and optical rest-frame showing a clumpy morphology in the continuum as well as line emission covering the entire galaxy over a range of 5 kpc from the central clump to the tail region. We analyze the integrated spectrum as well as different apertures in the galaxy allowing a spatially resolved characterization of the ionized ISM of this galaxy. We compare our measurements with archival NIRCam imaging and ALMA data. We measure a total star formation rate of 13.4 $\pm$ 1.8 Msun yr$^{-1}$, a metallicity of 12+log(O/H) = 7.84 $\pm$ 0.05 and $\xi_{ion}$= 25.4 $\pm$ 0.1 erg$^{-1}$ Hz and a burstiness parameter of 0.9 $\pm$ 0.1 for the integrated spectrum. We find large spatial differences in these parameters between the central clump and the tail region. The optical [OIII] emission peaks in the main galaxy, the far-infrared [OIII] emission peaks towards the tail, indicating different physical conditions in the ISM of the tail and main galaxy. This study presents the spatially resolved ISM analyses of a galaxy at z>9, revealing nebular line emission and strong spatial variations in star formation, metallicity, physical conditions, and ionizing efficiency. The results indicate a recent, metal-poor starburst in a tail alongside a more evolved, enriched central clump with evidence for extreme excitation. This demonstrates the power of spatially resolved JWST spectroscopy of galaxies in the Epoch of Reionization.

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Arjan Bik, Javier Álvarez-Márquez, Alejandro Crespo Gómez, Luis Colina, Pablo G. Pérez-González, Göran Östlin, Carmen Blanco Prieto, Jens Melinder, Danial Langeroodi, Gillian Wright, Hiddo S. B. Algera, Leindert A. Boogaard, Karina Caputi, Steven Gillman, Thomas Greve, Jens Hjorth, Edoardo Iani, Sarah Kendrew, Alvaro Labiano Ortega, Michele Perna, Carlota Prieto Jimenez, John Pye, Pierluigi Rinaldi, Paul van der Werf, Fabian Walter, Florian Peißker, Andreas Eckart, Thomas Henning, Manuel Güdel. 2026-04-24. Spatially resolved metallicity and ionization in the merging system Gz9p3 at z=9.3. https://arxiv.org/abs/2604.22460

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