REBELS-IFU: Spatially Resolved Ionizing Photon Production Efficiencies of 12 Bright Galaxies in the Epoch of Reionization
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2025
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| author | Komarova, Lena Stefanon, Mauro Laza-Ramos, Andres Algera, Hiddo S. Aravena, Manuel Bouwens, Rychard J. Bowler, Rebecca da Cunha, Elisabete Dayal, Pratika Ferrara, Andrea Fisher, Rebecca Nanayakkara, Themiya Rowland, Lucie E. Schouws, Sander Smit, Renske Sommovigo, Laura Stark, Daniel P. van der Werf, Paul |
| author_facet | Komarova, Lena Stefanon, Mauro Laza-Ramos, Andres Algera, Hiddo S. Aravena, Manuel Bouwens, Rychard J. Bowler, Rebecca da Cunha, Elisabete Dayal, Pratika Ferrara, Andrea Fisher, Rebecca Nanayakkara, Themiya Rowland, Lucie E. Schouws, Sander Smit, Renske Sommovigo, Laura Stark, Daniel P. van der Werf, Paul |
| contents | Measuring the ionizing photon production efficiency $ξ_{\mathrm{ion,0}}$ -- the ratio of ionizing photon output rate $Q_{\rm H^0}$ to UV continuum luminosity $L_{\rm UV}$ -- in galaxies at $z > 6$ is crucial for constraining their contribution to cosmic reionization. We present integrated and spatially resolved measurements of $ξ_{\mathrm{ion,0}}$ for 12 exceptionally bright ($M_\mathrm{UV} \sim -22$ mag) star-forming galaxies at $z \sim 7$ from the REBELS survey. These measurements are based on JWST NIRSpec/IFU PRISM spectroscopy, probing the rest-frame UV and optical regime. Notably, in 8 of the 12 galaxies, the spectral coverage includes H$α$, enabling self-consistent dust attenuation estimates in both the ionized gas and stellar continuum via the Balmer decrement and rest-UV slope, respectively. We find global $\logξ_{\mathrm{ion,0}}$ values ranging from $25.19\pm0.11$ to $25.61\pm0.11$, with a weighted mean of $25.44\pm0.15$, consistent with the canonical value of $\sim25.3$. Using a sample of 25 star-forming clumps within these galaxies, we explore local variations in LyC production efficiency, finding a broader range, from $24.52\pm0.21$ to $26.18\pm0.61$. We identify strong correlations between $ξ_{\mathrm{ion,0}}$ and specific star formation rate, star formation surface density, H$β$ equivalent width, and stellar mass. Clumps with the highest $ξ_{\mathrm{ion,0}}$ exhibit $\mathrm{EW}_0(\mathrm{H}β) \ge 150$ Angstrom, consistent with young stellar ages. From previous Ly$α$ measurements in three galaxies, we estimate a typical Ly$α$ escape fraction of $f_{\rm esc, Lyα} \sim 2\%$, suggesting similar or lower escape fractions for LyC photons. Combining this with our H$α$ measurements, we infer ionized bubble sizes $\sim 1$ pMpc, aligned with expectations from Ly$α$-detected systems and reionization models. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2511_10743 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | REBELS-IFU: Spatially Resolved Ionizing Photon Production Efficiencies of 12 Bright Galaxies in the Epoch of Reionization Komarova, Lena Stefanon, Mauro Laza-Ramos, Andres Algera, Hiddo S. Aravena, Manuel Bouwens, Rychard J. Bowler, Rebecca da Cunha, Elisabete Dayal, Pratika Ferrara, Andrea Fisher, Rebecca Nanayakkara, Themiya Rowland, Lucie E. Schouws, Sander Smit, Renske Sommovigo, Laura Stark, Daniel P. van der Werf, Paul Astrophysics of Galaxies Measuring the ionizing photon production efficiency $ξ_{\mathrm{ion,0}}$ -- the ratio of ionizing photon output rate $Q_{\rm H^0}$ to UV continuum luminosity $L_{\rm UV}$ -- in galaxies at $z > 6$ is crucial for constraining their contribution to cosmic reionization. We present integrated and spatially resolved measurements of $ξ_{\mathrm{ion,0}}$ for 12 exceptionally bright ($M_\mathrm{UV} \sim -22$ mag) star-forming galaxies at $z \sim 7$ from the REBELS survey. These measurements are based on JWST NIRSpec/IFU PRISM spectroscopy, probing the rest-frame UV and optical regime. Notably, in 8 of the 12 galaxies, the spectral coverage includes H$α$, enabling self-consistent dust attenuation estimates in both the ionized gas and stellar continuum via the Balmer decrement and rest-UV slope, respectively. We find global $\logξ_{\mathrm{ion,0}}$ values ranging from $25.19\pm0.11$ to $25.61\pm0.11$, with a weighted mean of $25.44\pm0.15$, consistent with the canonical value of $\sim25.3$. Using a sample of 25 star-forming clumps within these galaxies, we explore local variations in LyC production efficiency, finding a broader range, from $24.52\pm0.21$ to $26.18\pm0.61$. We identify strong correlations between $ξ_{\mathrm{ion,0}}$ and specific star formation rate, star formation surface density, H$β$ equivalent width, and stellar mass. Clumps with the highest $ξ_{\mathrm{ion,0}}$ exhibit $\mathrm{EW}_0(\mathrm{H}β) \ge 150$ Angstrom, consistent with young stellar ages. From previous Ly$α$ measurements in three galaxies, we estimate a typical Ly$α$ escape fraction of $f_{\rm esc, Lyα} \sim 2\%$, suggesting similar or lower escape fractions for LyC photons. Combining this with our H$α$ measurements, we infer ionized bubble sizes $\sim 1$ pMpc, aligned with expectations from Ly$α$-detected systems and reionization models. |
| title | REBELS-IFU: Spatially Resolved Ionizing Photon Production Efficiencies of 12 Bright Galaxies in the Epoch of Reionization |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2511.10743 |