A double-peaked Lyman-α emitter with a stronger blue peak multiply imaged by the galaxy cluster RXC J0018.5+1626

International audienceWe report the discovery of a double-peaked Lyman-α (Lyα) emitter (LAE) at z = 3.2177 ± 0.0001 in VLT/MUSE data. The galaxy is strongly lensed by the galaxy cluster RXC J0018.5+1626 recently observed in the RELICS survey, and the double-peaked Lyα emission is clearly detected in the two counter images in the MUSE field-of-view. We measure a relatively high Lyα rest-frame equivalent width (EW) of EWLyα, 0 = (63 ± 2) Å. Additional spectroscopy with Gemini/GNIRS in the near-infrared (NIR) allows us to measure the Hβ, [O III]λ4959Å and [O III]λ5007Å emission lines, which show moderate rest-frame EWs of the order of a few ~10 - 100 Å, an [O III]λ5007Å/Hβ ratio of 4.8 ± 0.7, and a lower limit on the [O III]/[O II] ratio of >9.3. The galaxy has very blue UV-continuum slopes of βFUV = -2.23 ± 0.06 and βNUV = -3.0 ± 0.2, and is magnified by factors μ ~ 7 - 10 in each of the two images, thus enabling a view into a low-mass (M⋆ ≃ 107.5 M⊙) high-redshift galaxy analog. Notably, the blue peak of the Lyα profile is significantly stronger than the red peak, which suggests an inflow of matter and possibly very low H I column densities in its circumgalactic gas. To the best of our knowledge, this is the first detection of such a Lyα profile. Combined with the high lensing magnification and image multiplicity, these properties make this galaxy a prime candidate for follow-up observations to search for LyC emission and constrain the LyC photon escape fraction