Quantifying the escape of Ly$α$ at $z\approx 5-6$: a census of Ly$α$ escape fraction with H$α$ emitting galaxies spectroscopically confirmed by JWST and VLT/MUSE
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| Natura: | Preprint |
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2024
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| _version_ | 1866914760109326336 |
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| author | Lin, Xiaojing Cai, Zheng Wu, Yunjing Li, Zihao Sun, Fengwu Fan, Xiaohui Chen, Zuyi Li, Mingyu Bian, Fuyan Ning, Yuanhang Jiang, Linhua Bruzual, Gustavo Charlot, Stephane Chevallard, Jacopo |
| author_facet | Lin, Xiaojing Cai, Zheng Wu, Yunjing Li, Zihao Sun, Fengwu Fan, Xiaohui Chen, Zuyi Li, Mingyu Bian, Fuyan Ning, Yuanhang Jiang, Linhua Bruzual, Gustavo Charlot, Stephane Chevallard, Jacopo |
| contents | JWST provides an unprecedented opportunity for unbiased surveys of H$α$-emitting galaxies at $z>4$ with the NIRCam wide-field slitless spectroscopy (WFSS). In this work, we present a census of Ly$α$ escape fraction ($f_{esc, Lyα}$) of 165 star-forming galaxies at $z=4.9-6.3$ using their H$α$ emission directly measured from FRESCO NIRCam/WFSS data. We search for Ly$α$ emission of each H$α$-emitting galaxy in VLT/MUSE data. The overall $f_{esc, Lyα}$ measured by stacking is $f_{esc, Lyα}$ is $0.090\pm0.006$. We find that $f_{esc, Lyα}$ displays a strong dependence on the observed UV slope ($β_{\rm obs}$) and E(B-V), such that the bluest galaxies ($β_{\rm obs}\sim-2.5$) have the largest escape fractions ($f_{\rm esc, Lyα}\approx0.6$), indicative of the crucial role of dust and gas in modulating the escape of Ly$α$ photons. $f_{esc, Lyα}$ is less well related to other parameters, including the UV luminosity and stellar mass, and the variation in $f_{esc, Lyα}$ with them can be explained by their underlying coupling with E(B-V) or $β_{\rm obs}$. Our results suggest a tentative decline in $f_{esc, Lyα}$ at $z\gtrsim 5$, implying increasing intergalactic medium attenuation towards higher redshift. Furthermore, the dependence of $f_{esc, Lyα}$ on $β_{\rm obs}$ is proportional to that of the ionizing photon escape fraction ($f_{\rm esc, LyC}$), indicating the escape of Ly$α$ and ionizing photon may be regulated by similar physical processes. With $f_{esc, Lyα}$ as a proxy to $f_{\rm esc, LyC}$, we infer that UV-faint ($M_{\rm UV}>-16$) galaxies contribute $>70\%$ of the total ionizing emissivity at $z=5-6$. If these relations hold during the epoch of reionization, UV-faint galaxies can contribute the majority of UV photon budget to reionize the Universe. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2401_09532 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Quantifying the escape of Ly$α$ at $z\approx 5-6$: a census of Ly$α$ escape fraction with H$α$ emitting galaxies spectroscopically confirmed by JWST and VLT/MUSE Lin, Xiaojing Cai, Zheng Wu, Yunjing Li, Zihao Sun, Fengwu Fan, Xiaohui Chen, Zuyi Li, Mingyu Bian, Fuyan Ning, Yuanhang Jiang, Linhua Bruzual, Gustavo Charlot, Stephane Chevallard, Jacopo Astrophysics of Galaxies Cosmology and Nongalactic Astrophysics JWST provides an unprecedented opportunity for unbiased surveys of H$α$-emitting galaxies at $z>4$ with the NIRCam wide-field slitless spectroscopy (WFSS). In this work, we present a census of Ly$α$ escape fraction ($f_{esc, Lyα}$) of 165 star-forming galaxies at $z=4.9-6.3$ using their H$α$ emission directly measured from FRESCO NIRCam/WFSS data. We search for Ly$α$ emission of each H$α$-emitting galaxy in VLT/MUSE data. The overall $f_{esc, Lyα}$ measured by stacking is $f_{esc, Lyα}$ is $0.090\pm0.006$. We find that $f_{esc, Lyα}$ displays a strong dependence on the observed UV slope ($β_{\rm obs}$) and E(B-V), such that the bluest galaxies ($β_{\rm obs}\sim-2.5$) have the largest escape fractions ($f_{\rm esc, Lyα}\approx0.6$), indicative of the crucial role of dust and gas in modulating the escape of Ly$α$ photons. $f_{esc, Lyα}$ is less well related to other parameters, including the UV luminosity and stellar mass, and the variation in $f_{esc, Lyα}$ with them can be explained by their underlying coupling with E(B-V) or $β_{\rm obs}$. Our results suggest a tentative decline in $f_{esc, Lyα}$ at $z\gtrsim 5$, implying increasing intergalactic medium attenuation towards higher redshift. Furthermore, the dependence of $f_{esc, Lyα}$ on $β_{\rm obs}$ is proportional to that of the ionizing photon escape fraction ($f_{\rm esc, LyC}$), indicating the escape of Ly$α$ and ionizing photon may be regulated by similar physical processes. With $f_{esc, Lyα}$ as a proxy to $f_{\rm esc, LyC}$, we infer that UV-faint ($M_{\rm UV}>-16$) galaxies contribute $>70\%$ of the total ionizing emissivity at $z=5-6$. If these relations hold during the epoch of reionization, UV-faint galaxies can contribute the majority of UV photon budget to reionize the Universe. |
| title | Quantifying the escape of Ly$α$ at $z\approx 5-6$: a census of Ly$α$ escape fraction with H$α$ emitting galaxies spectroscopically confirmed by JWST and VLT/MUSE |
| topic | Astrophysics of Galaxies Cosmology and Nongalactic Astrophysics |
| url | https://arxiv.org/abs/2401.09532 |