Lyman-alpha emission at the end of reionization: line strengths and profiles from MMT and JWST observations at z~5-6
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| Main Authors: | , , , , , , , , , , |
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| Format: | Preprint |
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2025
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| _version_ | 1866918145825964032 |
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| author | Prieto-Lyon, Gonzalo Mason, Charlotte A. Strait, Victoria Brammer, Gabriel Naidu, Rohan P. Meyer, Romain A. Oesch, Pascal Tacchella, Sandro Covelo-Paz, Alba Giovinazzo, Emma Xiao, Mengyuan |
| author_facet | Prieto-Lyon, Gonzalo Mason, Charlotte A. Strait, Victoria Brammer, Gabriel Naidu, Rohan P. Meyer, Romain A. Oesch, Pascal Tacchella, Sandro Covelo-Paz, Alba Giovinazzo, Emma Xiao, Mengyuan |
| contents | With JWST, it is now possible to use Lyman-Alpha (Ly$α$) emission from galaxies beyond z>8 to trace neutral hydrogen in the intergalactic medium (IGM) as the Universe became reionized. However, observed Ly$α$ emission is scattered by neutral hydrogen in the IGM and the interstellar and circum-galactic medium, necessitating `baseline' models of Ly$α$ properties in the ionized IGM to disentangle their impacts. In this work, we characterize Ly$α$ properties at the end of reionization, z~5-6, providing a baseline that can be applied to z>6 observations. We targeted GOODS-N with MMT/Binospec, obtaining R~4360 rest-frame UV spectra of 236 galaxies at z~5-6, selected from HST/CANDELS, finding 62 Ly$α$ detections. We use JWST observations from JADES and FRESCO for a subset of our sources to characterize Ly$α$ properties as a function of UV continuum and H$α$ emission. We present the first statistical measurements of the Ly$α$ FWHM distribution at z~5-6, and produce empirical baseline models of Ly$α$ equivalent width (EWLy$α$) and escape fraction (f$_{esc}^{Lyα}$) conditional on UV magnitude and slope. We find our EWLy$α$ and f$_{esc}^{Lyα}$ models depend on UV magnitude, and infer 45$\pm$5$\%$ and <62$\pm$8$\%$ of MUV=-19.5 galaxies have EWLy$α$>25$Å$ and f$_{esc}^{Lyα}$>0.2, respectively. We find a mean Ly$α$ FWHM of 245km/s and median Ly$α$ velocity offset of 258km/s, both correlating with higher UV luminosity. Our median observed Ly$α$ line profile is broader and has higher velocity offset compared to pre-JWST models based on z~2 lines, which may reflect resonant scattering by residual neutral hydrogen in the IGM at z~5-6 and increasing ISM/CGM densities. Our median line profile predicts higher Ly$α$ transmission in a fully neutral IGM, providing insight into recent z>10 Ly$α$ detections. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2509_18302 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Lyman-alpha emission at the end of reionization: line strengths and profiles from MMT and JWST observations at z~5-6 Prieto-Lyon, Gonzalo Mason, Charlotte A. Strait, Victoria Brammer, Gabriel Naidu, Rohan P. Meyer, Romain A. Oesch, Pascal Tacchella, Sandro Covelo-Paz, Alba Giovinazzo, Emma Xiao, Mengyuan Astrophysics of Galaxies With JWST, it is now possible to use Lyman-Alpha (Ly$α$) emission from galaxies beyond z>8 to trace neutral hydrogen in the intergalactic medium (IGM) as the Universe became reionized. However, observed Ly$α$ emission is scattered by neutral hydrogen in the IGM and the interstellar and circum-galactic medium, necessitating `baseline' models of Ly$α$ properties in the ionized IGM to disentangle their impacts. In this work, we characterize Ly$α$ properties at the end of reionization, z~5-6, providing a baseline that can be applied to z>6 observations. We targeted GOODS-N with MMT/Binospec, obtaining R~4360 rest-frame UV spectra of 236 galaxies at z~5-6, selected from HST/CANDELS, finding 62 Ly$α$ detections. We use JWST observations from JADES and FRESCO for a subset of our sources to characterize Ly$α$ properties as a function of UV continuum and H$α$ emission. We present the first statistical measurements of the Ly$α$ FWHM distribution at z~5-6, and produce empirical baseline models of Ly$α$ equivalent width (EWLy$α$) and escape fraction (f$_{esc}^{Lyα}$) conditional on UV magnitude and slope. We find our EWLy$α$ and f$_{esc}^{Lyα}$ models depend on UV magnitude, and infer 45$\pm$5$\%$ and <62$\pm$8$\%$ of MUV=-19.5 galaxies have EWLy$α$>25$Å$ and f$_{esc}^{Lyα}$>0.2, respectively. We find a mean Ly$α$ FWHM of 245km/s and median Ly$α$ velocity offset of 258km/s, both correlating with higher UV luminosity. Our median observed Ly$α$ line profile is broader and has higher velocity offset compared to pre-JWST models based on z~2 lines, which may reflect resonant scattering by residual neutral hydrogen in the IGM at z~5-6 and increasing ISM/CGM densities. Our median line profile predicts higher Ly$α$ transmission in a fully neutral IGM, providing insight into recent z>10 Ly$α$ detections. |
| title | Lyman-alpha emission at the end of reionization: line strengths and profiles from MMT and JWST observations at z~5-6 |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2509.18302 |