The resonant scattering interaction between Ly alpha photons and neutral hydrogen implies that a partially neutral intergalactic medium has the ability to significantly impact the detectability of Ly alpha emission in galaxies. Thus, the redshift evolution of the Ly alpha equivalent width distribution of galaxies offers a key observational probe of the degree of ionization during the Epoch of Reionization (EoR). Previous in-depth investigations at z >= 7 were limited by ground-based instrument capabilities. We present an extensive study of the evolution of Ly alpha emission from galaxies at 4.5 < z < 8.5, observed as part of the CEERS and JADES surveys in the JWST NIRSpec/PRISM configuration. The sample consists of 235 galaxies in the redshift range of 4.1 < z < 9.9. We identified 65 of them as Ly alpha emitters. We first measured the Ly alpha escape fractions from Ly alpha to Balmer line flux ratios and explored the correlations with the inferred galaxies' physical properties, which are similar to those found at lower redshift. We also investigated the possible connection between the escape of Ly alpha photons and the inferred escape fractions of LyC photons obtained from indirect indicators, finding no secure correlation. We then analyzed the redshift evolution of the Ly alpha emitter fraction, finding lower average values at z = 5 and 6 compared to previous ground-based observations. At z = 7, the GOODS-S results are aligned with previous findings, whereas the visibility in the EGS field appears to be enhanced. This discrepancy in Ly alpha visibility between the two fields could potentially be attributed to the presence of early reionized regions in the EGS. Such a broad variance is also expected in the Cosmic Dawn II radiation-hydrodynamical simulation. The average Ly alpha emitter fraction obtained from the CEERS+JADES data continues to increase from z = 5 to 7, ultimately declining at z = 8. This suggests a scenario in which the ending phase of the EoR is characterized by similar to 1 pMpc ionized bubbles around a high fraction of moderately bright galaxies. Finally, we characterize such two ionized regions found in the EGS at z = 7.18 and z = 7.49 by estimating the radius of the ionized bubble that each of the spectroscopically-confirmed members could have created.
Peering into cosmic reionization: Lyα visibility evolution from galaxies at z = 4.5–8.5 with JWST / Napolitano, L.; Pentericci, L.; Santini, P.; Calabrò, A.; Mascia, S.; Llerena, M.; Castellano, M.; Dickinson, M.; Finkelstein, S. L.; Amorín, R.; Arrabal Haro, P.; Bagley, M.; Bhatawdekar, R.; Cleri, N. J.; Davis, K.; Gardner, J. P.; Gawiser, E.; Giavalisco, M.; Hathi, N.; Holwerda, B. W.; Hu, W.; Jung, I.; Kartaltepe, J. S.; Koekemoer, A. M.; Larson, R. L.; Merlin, E.; Mobasher, B.; Papovich, C.; Park, H.; Pirzkal, N.; Trump, J. R.; Wilkins, S. M.; Yung, L. Y. A.. - In: ASTRONOMY & ASTROPHYSICS. - ISSN 1432-0746. - 688:(2024). [10.1051/0004-6361/202449644]
Peering into cosmic reionization: Lyα visibility evolution from galaxies at z = 4.5–8.5 with JWST
L. Napolitano
Primo
;
2024
Abstract
The resonant scattering interaction between Ly alpha photons and neutral hydrogen implies that a partially neutral intergalactic medium has the ability to significantly impact the detectability of Ly alpha emission in galaxies. Thus, the redshift evolution of the Ly alpha equivalent width distribution of galaxies offers a key observational probe of the degree of ionization during the Epoch of Reionization (EoR). Previous in-depth investigations at z >= 7 were limited by ground-based instrument capabilities. We present an extensive study of the evolution of Ly alpha emission from galaxies at 4.5 < z < 8.5, observed as part of the CEERS and JADES surveys in the JWST NIRSpec/PRISM configuration. The sample consists of 235 galaxies in the redshift range of 4.1 < z < 9.9. We identified 65 of them as Ly alpha emitters. We first measured the Ly alpha escape fractions from Ly alpha to Balmer line flux ratios and explored the correlations with the inferred galaxies' physical properties, which are similar to those found at lower redshift. We also investigated the possible connection between the escape of Ly alpha photons and the inferred escape fractions of LyC photons obtained from indirect indicators, finding no secure correlation. We then analyzed the redshift evolution of the Ly alpha emitter fraction, finding lower average values at z = 5 and 6 compared to previous ground-based observations. At z = 7, the GOODS-S results are aligned with previous findings, whereas the visibility in the EGS field appears to be enhanced. This discrepancy in Ly alpha visibility between the two fields could potentially be attributed to the presence of early reionized regions in the EGS. Such a broad variance is also expected in the Cosmic Dawn II radiation-hydrodynamical simulation. The average Ly alpha emitter fraction obtained from the CEERS+JADES data continues to increase from z = 5 to 7, ultimately declining at z = 8. This suggests a scenario in which the ending phase of the EoR is characterized by similar to 1 pMpc ionized bubbles around a high fraction of moderately bright galaxies. Finally, we characterize such two ionized regions found in the EGS at z = 7.18 and z = 7.49 by estimating the radius of the ionized bubble that each of the spectroscopically-confirmed members could have created.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
