New insight on the nature of cosmic reionizers from the CEERS survey

¹ INAF – Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monteporzio Catone, Italy
e-mail: sara.mascia@inaf.it
² Dipartimento di Fisica, Universitá di Roma Tor Vergata, Via della Ricerca Scientifica, 1, 00133 Roma, Italy
³ NSF’s National Optical-Infrared Astronomy Research Laboratory, 950 N. Cherry Ave., Tucson, AZ 85719, USA
⁴ Centro de Astrobiología (CAB), INTA-CSIC, Ctra de Ajalvir km 4, Torrejón de Ardoz, 28850 Madrid, Spain
⁵ Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
⁶ University of Massachusetts Amherst, 710 North Pleasant Street, Amherst, MA 01003-9305, USA
⁷ Astrophysics Science Division, NASA Goddard Space Flight Center, 8800 Greenbelt Rd, Greenbelt, MD 20771, USA
⁸ Department of Physics and Astronomy, Texas A&M University, College Station, TX 77843-4242, USA
⁹ George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Texas A&M University, College Station, TX 77843-4242, USA
¹⁰ European Space Agency (ESA), European Space Astronomy Centre (ESAC), Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
¹¹ Institute for Physics, Laboratory for Galaxy Evolution and Spectral Modelling, EPFL, Observatoire de Sauverny, Chemin Pegasi 51, 1290 Versoix, Switzerland
¹² INAF – Osservatorio Astronomico di Trieste, Via Tiepolo 11, 34131 Trieste, Italy
¹³ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
¹⁴ Department of Physics, University of Connecticut, 196A Auditorium Road, Unit 3046, Storrs, CT 06269, USA
¹⁵ Université de Strasbourg, CNRS, Observatoire Astronomique de Strasbourg (ObAS), 11 Rue de l’Université, Strasbourg, France
¹⁶ Physics & Astronomy Department, University of Louisville, Louisville, 40292 KY, USA
¹⁷ ARAID Foundation, Centro de Estudios de Física del Cosmos de Aragón (CEFCA), Unidad Asociada al CSIC, Plaza San Juan 1, 44001 Teruel, Spain
¹⁸ Departamento de Astronomía, Universidad de La Serena, Av. Juan Cisternas 1200 Norte, La Serena 1720236, Chile
¹⁹ Universität Heidelberg, Zentrum für Astronomie, Institut für Theoretische Astrophysik, Albert-Ueberle-Str. 2, 69120 Heidelberg, Germany
²⁰ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
²¹ Laboratory for Multiwavelength Astrophysics, School of Physics and Astronomy, Rochester Institute of Technology, 84 Lomb Memorial Drive, Rochester, NY 14623, USA
²² ESA/AURA Space Telescope Science Institute, Baltimore, USA
²³ Department of Astronomy, The University of Texas at Austin, Austin, TX, USA
²⁴ Astronomy Centre, University of Sussex, Falmer, Brighton BN1 9QH, UK
²⁵ Institute of Space Sciences and Astronomy, University of Malta, Msida 2080, Malta

Received: 5 September 2023
Accepted: 2 February 2024

Abstract

The Epoch of Reionization (EoR) began when galaxies grew in abundance and luminosity, so their escaping Lyman continuum (LyC) radiation started ionizing the surrounding neutral intergalactic medium (IGM). Despite significant recent progress, the nature and role of cosmic reionizers are still unclear: in order to define them, it would be necessary to directly measure their LyC escape fraction (f_esc). However, this is impossible during the EoR due to the opacity of the IGM. Consequently, many efforts at low and intermediate redshift have been made to determine measurable indirect indicators in high-redshift galaxies so that their f_esc can be predicted. This work presents the analysis of the indirect indicators of 62 spectroscopically confirmed star-forming galaxies at 6 ≤ z ≤ 9 from the Cosmic Evolution Early Release Science (CEERS) survey, combined with 12 sources with public data from other JWST-ERS campaigns. From the NIRCam and NIRSpec observations, we measured their physical and spectroscopic properties. We discovered that on average 6 < z < 9 star-forming galaxies are compact in the rest-frame UV (r_e ∼ 0.4 kpc), are blue sources (UV-β slope ∼ − 2.17), and have a predicted f_esc of about 0.13. A comparison of our results to models and predictions as well as an estimation of the ionizing budget suggests that low-mass galaxies with UV magnitudes fainter than M₁₅₀₀ = −18 that we currently do not characterize with JWST observations probably played a key role in the process of reionization.