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arXiv · 2507.08245

The JWST Spectroscopic Properties of Galaxies at $z=9-14$

Mengtao Tang·Daniel P. Stark·Charlotte A. Mason·Viola Gelli·Zuyi Chen·Michael W. Topping
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Abstract

We characterize the JWST spectra of $61$ galaxies at $z=9-14$, including $30$ newly-confirmed galaxies. We directly compare the $z>9$ spectroscopic properties against $401$ galaxies at $6 9$ galaxies. Our dataset indicates that the emission lines undergo a marked change at $z>9$, with extremely large CIII], H$\beta$, and H$\gamma$ EWs becoming $2-3\times$ more common at $z>9$ relative to $6 9$ galaxies. These results may reflect a larger dispersion in UV luminosity at fixed halo mass and larger baryon accretion rates at $z>9$, although other physical effects may also contribute. We suggest that the shift in star formation conditions explains the prevalence of extreme nebular spectra that have been detected at $z>9$, with hard ionizing sources and nitrogen-enhancements becoming more typical at the highest redshifts. Finally, we identify five $z>9$ spectroscopically confirmed galaxies with red UV colors ($\beta\gtrsim-1.5$), either revealing a small population with moderate dust attenuation ($\tau_V=0.23-0.35$) or very high density nebular-dominated galaxies with hot stellar populations.

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Mengtao Tang, Daniel P. Stark, Charlotte A. Mason, Viola Gelli, Zuyi Chen, Michael W. Topping. 2025-07-11. The JWST Spectroscopic Properties of Galaxies at $z=9-14$. https://arxiv.org/abs/2507.08245

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