The JWST Spectroscopic Properties of Galaxies at $z=9-14$
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2025
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| author | Tang, Mengtao Stark, Daniel P. Mason, Charlotte A. Gelli, Viola Chen, Zuyi Topping, Michael W. |
| author_facet | Tang, Mengtao Stark, Daniel P. Mason, Charlotte A. Gelli, Viola Chen, Zuyi Topping, Michael W. |
| contents | 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 $6<z<9$, with the goal of identifying evolution in the star formation histories and ISM. We measure rest-UV emission line properties and UV continuum slopes, while also investigating the rest-optical emission lines for the subset of galaxies at $9.0<z<9.6$. With these spectra, we constrain the stellar masses, specific star formation rates, dust attenuation, and the average metallicity and abundance pattern of $z>9$ galaxies. Our dataset indicates that the emission lines undergo a marked change at $z>9$, with extremely large CIII], H$β$, and H$γ$ EWs becoming $2-3\times$ more common at $z>9$ relative to $6<z<9$. Using the spectra, we infer the distribution of SFRs on short (SFR$_{\rm 3Myr}$) and medium (SFR$_{\rm 3-50Myr}$) timescales, finding that rapid SFR upturns (large SFR$_{\rm 3Myr}$/SFR$_{\rm 3-50Myr}$ ratios) are significantly more likely among $z>9$ 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 ($β\gtrsim-1.5$), either revealing a small population with moderate dust attenuation ($τ_V=0.23-0.35$) or very high density nebular-dominated galaxies with hot stellar populations. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2507_08245 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | The JWST Spectroscopic Properties of Galaxies at $z=9-14$ Tang, Mengtao Stark, Daniel P. Mason, Charlotte A. Gelli, Viola Chen, Zuyi Topping, Michael W. Astrophysics of Galaxies 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 $6<z<9$, with the goal of identifying evolution in the star formation histories and ISM. We measure rest-UV emission line properties and UV continuum slopes, while also investigating the rest-optical emission lines for the subset of galaxies at $9.0<z<9.6$. With these spectra, we constrain the stellar masses, specific star formation rates, dust attenuation, and the average metallicity and abundance pattern of $z>9$ galaxies. Our dataset indicates that the emission lines undergo a marked change at $z>9$, with extremely large CIII], H$β$, and H$γ$ EWs becoming $2-3\times$ more common at $z>9$ relative to $6<z<9$. Using the spectra, we infer the distribution of SFRs on short (SFR$_{\rm 3Myr}$) and medium (SFR$_{\rm 3-50Myr}$) timescales, finding that rapid SFR upturns (large SFR$_{\rm 3Myr}$/SFR$_{\rm 3-50Myr}$ ratios) are significantly more likely among $z>9$ 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 ($β\gtrsim-1.5$), either revealing a small population with moderate dust attenuation ($τ_V=0.23-0.35$) or very high density nebular-dominated galaxies with hot stellar populations. |
| title | The JWST Spectroscopic Properties of Galaxies at $z=9-14$ |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2507.08245 |