P. CassataL. MorselliA. FaisstM. GinolfiM. BétherminP. CapakO. Le FèvreD. SchaererJ. SilvermanL. YanB. C. LemauxM. RomanoM. TaliaS. BardelliM. BoquienA. CimattiM. Dessauges-ZavadskyY. FudamotoS. FujimotoM. GiavaliscoN. P. HathiIbar, EduardoEduardoIbarG. JonesA. M. KoekemoerH. Méndez-HernandezC. ManciniP. A. OeschF. PozziD. A. RiechersG. RodighieroD. VerganiG. ZamoraniE. Zucca2025-04-132025-04-132020-06-2410.1051/0004-6361/2020375172-s2.0-85095115617https://cris-uv-2.scimago.es/handle/123456789/2037WOS:000588070500006Context. The Lyman- α line in the ultraviolet (UV) and the [CII] line in the far-infrared (FIR) are widely used tools to identify galaxies in the early Universe and to obtain insights into interstellar medium (ISM) properties in high-redshift galaxies. By combining data obtained with ALMA in band 7 at ∼320 GHz as part of the ALMA Large Program to INvestigate [CII] at Early Times (ALPINE) with spectroscopic data from DEIMOS at the Keck Observatory, VIMOS and FORS2 at the Very Large Telescope, we assembled a unique sample of 53 main-sequence star-forming galaxies at 4.4 < z < 6 in which we detect both the Lyman- α line in the UV and the [CII] line in the FIR. Aims. The goal of this paper is to constrain the properties of the Ly α emission in these galaxies in relation to other properties of the ISM. Methods. We used [CII], observed with ALMA, as a tracer of the systemic velocity of the galaxies, and we exploited the available optical spectroscopy to obtain the Ly α -[CII] and ISM-[CII] velocity offsets. Results. We find that 90% of the selected objects have Ly α -[CII] velocity offsets in the range 0 < Δ v Ly α − [CII] < 400 km s −1 , in line with the few measurements available so far in the early Universe, and significantly smaller than those observed at lower redshifts. At the same time, we observe ISM-[CII] offsets in the range −500 < Δ v ISM−[CII] < 0 km s −1 , in line with values at all redshifts, which we interpret as evidence for outflows in these galaxies. We find significant anticorrelations between Δ v Ly α −[CII] and the Ly α rest-frame equivalent width EW 0 (Ly α ) (or equivalently, the Ly α escape fraction f esc (Ly α )): galaxies that show smaller Δ v Ly α −[CII] have larger EW 0 (Ly α ) and f esc (Ly α ). Conclusions. We interpret these results in the framework of available models for the radiative transfer of Ly α photons. According to the models, the escape of Ly α photons would be favored in galaxies with high outflow velocities, producing large EW 0 (Ly α ) and small Δ v Ly α -[CII] , in agreement with our observations. The uniform shell model would also predict that the Ly α escape in galaxies with slow outflows (0 < v out < 300 km s −1 ) is mainly determined by the neutral hydrogen column density (NHI) along the line of sight, while the alternative model by Steidel et al. (2010, ApJ, 717, 289) would more highly favor a combination of NHI at the systemic velocity and covering fraction as driver of the Ly α escape. We suggest that the increase in Ly α escape that is observed in the literature between z ∼ 2 and z ∼ 6 is not due to a higher incidence of fast outflows at high redshift, but rather to a decrease in average NHI along the line of sight, or alternatively, a decrease in HI covering fraction.enacceso abiertoAstronomy And AstrophysicsSpace And Planetary Sciencereview