MUSEQuBES: Calibrating the redshifts of Lyman-α emitters using stacked circumgalactic medium absorption profiles

International audienceLyman−α (Lyα) emission lines are typically found to be redshifted with respect to the systemic redshifts of galaxies, likely due to resonant scattering of Lyα photons. Here we measure the average velocity offset for a sample of 96 z ≈ 3.3 Lyα emitters (LAEs) with a median Lyα flux (luminosity) of ≈ 10 −17 erg cm −2 s −1 (≈ 10 42 erg s −1) and a median unobscured star formation rate (SFR) of ≈ 1.3 M yr −1 , detected by the Multi-Unit Spectroscopic Explorer as part of our MUSEQuBES circumgalactic medium (CGM) survey. By postulating that the stacked CGM absorption profiles of these LAEs, probed by 8 background quasars, must be centered on the systemic redshift, we measure an average velocity offset, V offset = 169 ± 10 km s −1 , between the Lyα emission peak and the systemic redshift. The observed V offset is lower by factors of ≈ 1.4 and ≈ 2.6 compared to the velocity offsets measured for narrow-band selected LAEs and Lyman break galaxies, respectively, which probe galaxies with higher masses and SFRs. Consistent with earlier studies based on direct measurements for individual objects, we find that the V offset is correlated with the full width at half-maximum of the red peak of the Lyα line, and anti-correlated with the rest-frame equivalent width. Moreover, we find that V offset is correlated with SFR with a sub-linear scaling relation, V offset ∝ SFR 0.16±0.03. Adopting the mass scaling for main sequence galaxies, such a relation suggests that V offset scales with the circular velocity of the dark matter halos hosting the LAEs