Peering into cosmic reionization: Lyα visibility evolution from galaxies at z = 4.5–8.5 with JWST

¹ INAF – Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monteporzio Catone, Italy
e-mail: lorenzo.napolitano@inaf.it
² Dipartimento di Fisica, Università di Roma Sapienza, Città Universitaria di Roma – Sapienza, Piazzale Aldo Moro, 2, 00185 Roma, Italy
³ Dipartimento di Fisica, Università di Roma Tor Vergata, Via della Ricerca Scientifica, 1, 00133 Roma, Italy
⁴ Department of Physics and Astronomy, Texas A&M University, College Station, TX 77843-4242, USA
⁵ George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Texas A&M University, College Station, TX 77843-4242, USA
⁶ Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218, USA
⁷ Department of Astronomy, The University of Texas at Austin, Austin, TX, USA
⁸ Astronomy Centre, University of Sussex, Falmer, Brighton BN1 9QH, UK
⁹ Institute of Space Sciences and Astronomy, University of Malta, Msida, MSD 2080, Malta
¹⁰ NSF’s National Optical-Infrared Astronomy Research Laboratory, 950 N. Cherry Ave., Tucson, AZ 85719, USA
¹¹ Department of Physics, 196A Auditorium Road, Unit 3046, University of Connecticut, Storrs, CT 06269, USA
¹² Department of Physics and Astronomy, Rutgers University, Piscataway, NJ 08854, USA
¹³ Departamento de Astronomía, Universidad de La Serena, Av. Juan Cisternas 1200 Norte, La Serena, Chile
¹⁴ ARAID Foundation, Centro de Estudios de Física del Cosmos de Aragón (CEFCA), Unidad Asociada al CSIC, Plaza San Juan 1, 44001 Teruel, Spain
¹⁵ Laboratory for Multiwavelength Astrophysics, School of Physics and Astronomy, Rochester Institute of Technology, 84 Lomb Memorial Drive, Rochester, NY 14623, USA
¹⁶ ESA/AURA Space Telescope Science Institute, USA
¹⁷ University of Massachusetts Amherst, 710 North Pleasant Street, Amherst, MA 01003-9305, USA
¹⁸ Department of Physics and Astronomy, University of California Riverside, 900 University Avenue, Riverside, CA 92521, USA
¹⁹ European Space Agency (ESA), European Space Astronomy Centre (ESAC), Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
²⁰ Astrophysics Science Division, NASA Goddard Space Flight Center, 8800 Greenbelt Rd, Greenbelt, MD 20771, USA
²¹ Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
²² Department of Physics and Astronomy, University of Louisville, Natural Science Building 102, 40292 KY, Louisville, USA

Received: 17 February 2024
Accepted: 19 April 2024

Abstract

The resonant scattering interaction between Lyα photons and neutral hydrogen implies that a partially neutral intergalactic medium has the ability to significantly impact the detectability of Lyα emission in galaxies. Thus, the redshift evolution of the Lyα 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 Lyα 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 Lyα emitters. We first measured the Lyα escape fractions from Lyα 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 Lyα 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 Lyα 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 Lyα 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 Lyα 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 ∼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.