View of the UV absorption lines and the UV peak velocity of BOSS-EUVLG1. Left panel: comparison between the Hα emission and the UV ISM absorption lines. Upper left panel: normalized Hα spectrum (black line), together with the narrow (red line) and broad (blue line) Hα components. Bottom left panel: UV ISM absorption lines for two different ionization states. Orange line: combination of UV ISM absorption lines of partially neutral elements (Si II 1260 Å, C II 1334 Å, and Si II 1526 Å). Green line: combination of UV ISM absorption lines of high ionization elements (Si IV 1393,1402 Å). Both lines are normalized in a spectral windows clean of absorption and emission features. The peak velocities of both UV absorption ionization states and the broad Hα component are shown as color-coded vertical lines. Right panel: peak velocity of the UV low-ionization ISM absorption lines as a function of the UV absolute magnitude. Yellow star: BOSS-EUVLG1. Blue dots: Lyman alpha emitters (Patrício et al. 2016; Marques-Chaves et al. 2020b). Red squares: Lyman break galaxies (Pettini et al. 2000; Quider et al. 2009, 2010; Dessauges-Zavadsky et al. 2010; Marques-Chaves et al. 2018).