The Impact of Galaxy Overdensities and Ionized Bubbles on Ly$α$ Emission at $z\sim7.0-8.5$
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2025
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| author | Chen, Zuyi Stark, Daniel P. Mason, Charlotte A. Tang, Mengtao Whitler, Lily Lu, Ting-Yi Topping, Michael W. |
| author_facet | Chen, Zuyi Stark, Daniel P. Mason, Charlotte A. Tang, Mengtao Whitler, Lily Lu, Ting-Yi Topping, Michael W. |
| contents | Ly$α$ spectroscopy with JWST is opening a new window on the sizes of ionized bubbles through the reionization epoch. Theoretical expectations suggest typical bubble radii should be 0.6-1.5 pMpc at $z\simeq 7$, assuming neutral hydrogen fractions of the intergalactic medium in the range $\overline{x}_{\rm HI}$=0.5-0.7. Here we investigate this picture using JWST to characterize the environment and Ly$α$ emission of 292 galaxies at $7.0<z<8.5$ across 5 fields spanning a comoving volume of $1.3\times10^6$ Mpc$^3$. If the reionization predictions are correct, we should see overdensities and strong Ly$α$ emission clustered in redshift windows of d$z=0.04-0.08$ and angular scales of 5-11 arcmin. We detect Ly$α$ emission in 36 out of 292 galaxies, including nine new Ly$α$ detections, two of which (in the UDS field) show extremely large equivalent widths (EW = $200_{-78}^{+50}$ A and $284_{-75}^{+56}$ A). We identify 13 significant (4-11$\times$) galaxy overdensities using redshifts from NIRCam grism and NIRSpec. Strong Ly$α$ emitters are almost uniformly found in the overdensities, with nearly all located between the center and back of the structures. The overdensities that host the strong Ly$α$ emitters span typical line-of-sight distances (d$z\sim 0.14$) and angular scales ($\sim 8$ arcmin) that are comparable to the predicted bubble sizes at $z\simeq 7$. We discuss evidence that the EGS is mostly ionized along a 24 pMpc sightline at $z\simeq 7.0-7.6$, based on the presence of 3 overdense structures and 10 Ly$α$ emitters in this volume, and find such a large ionized region would pose tension with standard reionization models. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2505_24080 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | The Impact of Galaxy Overdensities and Ionized Bubbles on Ly$α$ Emission at $z\sim7.0-8.5$ Chen, Zuyi Stark, Daniel P. Mason, Charlotte A. Tang, Mengtao Whitler, Lily Lu, Ting-Yi Topping, Michael W. Astrophysics of Galaxies Cosmology and Nongalactic Astrophysics Ly$α$ spectroscopy with JWST is opening a new window on the sizes of ionized bubbles through the reionization epoch. Theoretical expectations suggest typical bubble radii should be 0.6-1.5 pMpc at $z\simeq 7$, assuming neutral hydrogen fractions of the intergalactic medium in the range $\overline{x}_{\rm HI}$=0.5-0.7. Here we investigate this picture using JWST to characterize the environment and Ly$α$ emission of 292 galaxies at $7.0<z<8.5$ across 5 fields spanning a comoving volume of $1.3\times10^6$ Mpc$^3$. If the reionization predictions are correct, we should see overdensities and strong Ly$α$ emission clustered in redshift windows of d$z=0.04-0.08$ and angular scales of 5-11 arcmin. We detect Ly$α$ emission in 36 out of 292 galaxies, including nine new Ly$α$ detections, two of which (in the UDS field) show extremely large equivalent widths (EW = $200_{-78}^{+50}$ A and $284_{-75}^{+56}$ A). We identify 13 significant (4-11$\times$) galaxy overdensities using redshifts from NIRCam grism and NIRSpec. Strong Ly$α$ emitters are almost uniformly found in the overdensities, with nearly all located between the center and back of the structures. The overdensities that host the strong Ly$α$ emitters span typical line-of-sight distances (d$z\sim 0.14$) and angular scales ($\sim 8$ arcmin) that are comparable to the predicted bubble sizes at $z\simeq 7$. We discuss evidence that the EGS is mostly ionized along a 24 pMpc sightline at $z\simeq 7.0-7.6$, based on the presence of 3 overdense structures and 10 Ly$α$ emitters in this volume, and find such a large ionized region would pose tension with standard reionization models. |
| title | The Impact of Galaxy Overdensities and Ionized Bubbles on Ly$α$ Emission at $z\sim7.0-8.5$ |
| topic | Astrophysics of Galaxies Cosmology and Nongalactic Astrophysics |
| url | https://arxiv.org/abs/2505.24080 |