Ly$α$ visibility from z = 4.5 to 11 in the UDS field: Evidence for a high neutral hydrogen fraction and small ionized bubbles at z $\sim$ 7
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2025
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| author | Napolitano, L. Pentericci, L. Dickinson, M. Haro, P. Arrabal Taylor, A. J. Calabrò, A. Bhagwat, A. Santini, P. Arevalo-Gonzalez, F. Begley, R. Castellano, M. Ciardi, B. Donnan, C. T. Dottorini, D. Dunlop, J. S. Finkelstein, S. L. Fontana, A. Giavalisco, M. Hirschmann, M. Jung, I. Koekemoer, A. M. Kokorev, V. Llerena, M. Lucas, R. A. Mascia, S. Merlin, E. Pérez-González, P. G. Stanton, T. M. Tripodi, R. Wang, X. Weiner, B. J. |
| author_facet | Napolitano, L. Pentericci, L. Dickinson, M. Haro, P. Arrabal Taylor, A. J. Calabrò, A. Bhagwat, A. Santini, P. Arevalo-Gonzalez, F. Begley, R. Castellano, M. Ciardi, B. Donnan, C. T. Dottorini, D. Dunlop, J. S. Finkelstein, S. L. Fontana, A. Giavalisco, M. Hirschmann, M. Jung, I. Koekemoer, A. M. Kokorev, V. Llerena, M. Lucas, R. A. Mascia, S. Merlin, E. Pérez-González, P. G. Stanton, T. M. Tripodi, R. Wang, X. Weiner, B. J. |
| contents | The resonant scattering nature of Ly$α$ photons interacting with neutral hydrogen makes Ly$α$ emitters (LAEs) robust tracers of the intergalactic neutral hydrogen fraction, and thus sensitive probes of cosmic reionization. We present an extensive study of the Ly$α$ evolution from galaxies at 4.5 $\leq$ z $\leq$ 11 in the UDS field, observed as part of the CAPERS survey, and complemented with spectra from the DAWN JWST Archive. The combined sample includes 651 spectroscopically confirmed Ly$α$-break galaxies, among which we find 73 S/N>3 LAEs in JWST-NIRSpec PRISM spectra. We trace the redshift evolution of the LAE fraction with EW$_0$ >25 A (X$_{\mathrm{Lyα}}$) between z = 5 and z = 9, extending such an analysis to the UDS field for the first time. At z = 5 and 6, the UDS results agree with the average JWST X$_{\mathrm{Lyα}}$ values from multiple fields. However, JWST measurements are consistently lower than ground-based results. To investigate this, we compare JWST observations to a population of star-forming galaxies at z$\sim$6 observed with VLT-FORS2. We find that a Ly$α$ slit-loss of 35 $\pm$ 10% in JWST spectra accounts for the offset, as the resonant Ly$α$ emission is more spatially extended than the stellar continuum. From z = 6 to 7, the UDS field shows a significant drop in Ly$α$ visibility, from which we infer a neutral hydrogen fraction of X$_{\mathrm{HI}}$ = 0.7--0.9. Finally, we identify two robust ionized bubbles at z = 7.29 and 7.77, with radii of $R_{\mathrm{ion}}$ = 0.6 and 0.5 physical Mpc and photometric overdensities of N/$\langle$N$\rangle$ = 3 and 4, based on candidate counts down to the photometric completeness limit. Compared to the large ionized region at z$\sim$7 in the EGS field, these results indicate significant field-to-field variation, supporting a patchy, inhomogeneous reionization process. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2508_14171 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Ly$α$ visibility from z = 4.5 to 11 in the UDS field: Evidence for a high neutral hydrogen fraction and small ionized bubbles at z $\sim$ 7 Napolitano, L. Pentericci, L. Dickinson, M. Haro, P. Arrabal Taylor, A. J. Calabrò, A. Bhagwat, A. Santini, P. Arevalo-Gonzalez, F. Begley, R. Castellano, M. Ciardi, B. Donnan, C. T. Dottorini, D. Dunlop, J. S. Finkelstein, S. L. Fontana, A. Giavalisco, M. Hirschmann, M. Jung, I. Koekemoer, A. M. Kokorev, V. Llerena, M. Lucas, R. A. Mascia, S. Merlin, E. Pérez-González, P. G. Stanton, T. M. Tripodi, R. Wang, X. Weiner, B. J. Astrophysics of Galaxies Cosmology and Nongalactic Astrophysics The resonant scattering nature of Ly$α$ photons interacting with neutral hydrogen makes Ly$α$ emitters (LAEs) robust tracers of the intergalactic neutral hydrogen fraction, and thus sensitive probes of cosmic reionization. We present an extensive study of the Ly$α$ evolution from galaxies at 4.5 $\leq$ z $\leq$ 11 in the UDS field, observed as part of the CAPERS survey, and complemented with spectra from the DAWN JWST Archive. The combined sample includes 651 spectroscopically confirmed Ly$α$-break galaxies, among which we find 73 S/N>3 LAEs in JWST-NIRSpec PRISM spectra. We trace the redshift evolution of the LAE fraction with EW$_0$ >25 A (X$_{\mathrm{Lyα}}$) between z = 5 and z = 9, extending such an analysis to the UDS field for the first time. At z = 5 and 6, the UDS results agree with the average JWST X$_{\mathrm{Lyα}}$ values from multiple fields. However, JWST measurements are consistently lower than ground-based results. To investigate this, we compare JWST observations to a population of star-forming galaxies at z$\sim$6 observed with VLT-FORS2. We find that a Ly$α$ slit-loss of 35 $\pm$ 10% in JWST spectra accounts for the offset, as the resonant Ly$α$ emission is more spatially extended than the stellar continuum. From z = 6 to 7, the UDS field shows a significant drop in Ly$α$ visibility, from which we infer a neutral hydrogen fraction of X$_{\mathrm{HI}}$ = 0.7--0.9. Finally, we identify two robust ionized bubbles at z = 7.29 and 7.77, with radii of $R_{\mathrm{ion}}$ = 0.6 and 0.5 physical Mpc and photometric overdensities of N/$\langle$N$\rangle$ = 3 and 4, based on candidate counts down to the photometric completeness limit. Compared to the large ionized region at z$\sim$7 in the EGS field, these results indicate significant field-to-field variation, supporting a patchy, inhomogeneous reionization process. |
| title | Ly$α$ visibility from z = 4.5 to 11 in the UDS field: Evidence for a high neutral hydrogen fraction and small ionized bubbles at z $\sim$ 7 |
| topic | Astrophysics of Galaxies Cosmology and Nongalactic Astrophysics |
| url | https://arxiv.org/abs/2508.14171 |