Super-early JWST galaxies, outflows, and Lyα visibility in the Epoch of Reionization

Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa, Italy
e-mail: andrea.ferrara@sns.it

Received: 19 October 2023
Accepted: 8 February 2024

Abstract

The overabundance of super-early (redshift z > 10) luminous (M_UV < −20) blue galaxies detected by JWST has been explained as being due to negligible dust attenuation in these systems. We show that this model correctly reproduces the UV luminosity function at z > 10 and the star formation rate (SFR) density evolution. The model also predicts, in agreement with data, that the cosmic specific SFR (sSFR) grows as sSFR ∝ (1 + z)^3/2. At z ≃ 10, the cosmic sSFR crosses the critical value sSFR^⋆ = 25 Gyr⁻¹, and approximately 45% of the galaxies become super-Eddington, driving outflows reaching velocities of ≈830(ϵ_⋆/f_M)^1/2 km s⁻¹, where ϵ_⋆ and f_M are the star formation efficiency and fraction of the halo gas expelled in the outflow, respectively. This prediction is consistent with the outflow velocities measured in 12 super-Eddington galaxies of the JWST/JADES sample. Such outflows clear the dust, thus boosting the galaxy luminosity. They also dramatically enhance the visibility of the Lyα line from z > 10 galaxies by introducing a velocity offset. The observed Lyα properties in GN-z11 (z = 10.6) are simultaneously recovered by the outflow model if log N_HI ≃ 20.1, implying that the outflow is largely ionized. We make analogous predictions for the Lyα visibility of other super-early galaxies, and we compare the model with Lyα surveys at z > 7, finding that essentially all super-Eddington (sub-Eddington) galaxies are (not) detected in Lyα. Finally, the sSFR positively correlates with the LyC escape fraction, as outflows carve ionized transparent channels through which LyC photons leak.