A resolved Lyman α profile with doubly peaked emission at z ∼ 7

¹ Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Santiago, 7820436, Chile
² Las Campanas Observatory, Carnegie Institution of Washington, Casilla 601, La Serena, Chile
³ Instituto de Estudios Astrofísicos, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejército Libertador 441, Santiago, 8370191, Chile
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 Astrophysics Science Division, NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, Maryland 20771, USA
⁷ CAS Key Laboratory for Research in Galaxies and Cosmology, Department of Astronomy, University of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China
⁸ School of Astronomy and Space Science, University of Science and Technology of China, Hefei, 230026, People ’s Republic of China
⁹ CAS Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Shanghai, 200030, People’s Republic of China

^⋆ Corresponding author; cnmoya@uc.cl

Received: 14 May 2024
Accepted: 5 November 2024

Abstract

Context. The epoch of reionization is a landmark in structure formation and galaxy evolution. How it happened is still not clear, especially regarding which population of objects was responsible for contributing the bulk of ionizing photons to this process. Doubly peaked Lyman-alpha profiles in this epoch are of particular interest since they hold information about the escape of ionizing radiation and the environment surrounding the source.

Aims. We wish to understand the escape mechanisms of ionizing radiation in Lyα emitters during this time and the origin of a doubly peaked Lyman-alpha profile. We also wish to estimate the size of a potential ionized bubble.

Methods. Using radiative transfer models, we fit the line profile of a bright Lyα emitter at z ∼ 6.9 using various gas geometries. The line modeling reveals significant radiation escape from this system.

Results. The studied source shows significant escape (f_esc(Lyα) ∼ 0.8, as predicted by the best fitting radiative transfer model) and appears to inhabit an ionized bubble of radius R_b ≈ 0.8_−0.3^+0.5 pMpc(t_age/10⁸)^1/3. Radiative transfer modeling predicts the line to be completely redward of the systemic redshift. We suggest the line morphology is produced by inflows, by multiple components emitting Lyα, or by an absorbing component in the red wing.

Conclusions. We propose that CDFS-1’s profile has two red peaks produced by winds within the system. Its high f_esc(Lyα) and the low-velocity offset from the systemic redshift suggest that the source is an active ionizing agent. Future observations will reveal whether a peak is present blueward of the systemic redshift or if multiple components produce the profile.