2022A&A...664L...5B

GN-108036 is a star-forming galaxy at z = 7.21, and one of the most distant known sources in the Northern hemisphere. Based on observations from the NOrthern Extended Millimeter Array (NOEMA), here we report the tentative detection of the [CII] line at ≃4σ significance. The integrated [CII] line emission is spatially offset about ∼4 kpc from the rest-frame ultraviolet (UV) emission. The total [CII] luminosity (L_[CII] = 2.7 x 10⁸ L_☉) is consistent with the relation between [CII] luminosity and star formation rate (SFR) observed in nearby and high-z star forming galaxies. More interestingly, the [CII] line is blueshifted with respect to the Lyα line by 980 ± 10 km/s. If confirmed, this corresponds to the largest velocity offset reported to date between the Lyα line and a non-resonant line at z ≥ 6. According to trends observed in other high redshift galaxies, the large Lyα velocity offset in GN-108036 is consistent with its low Lyα equivalent width and high UV absolute magnitude. Based on Lyα radiative transfer models of expanding shells, the large Lyα velocity offset in GN-108036 could be interpreted as the presence of a large column density of hydrogen gas, and/or an outflow with a velocity of v_out ∼ Δv_Lyα/2 ∼ 500 km/s. We also report the 3σ detection of a potential galaxy companion located ∼30 kpc east of GN-108036, at a similar systemic velocity, and with no counterpart rest-frame UV emission.