Observed Hα emission of BOSS-EUVLG1. Upper panel: near-IR 2D calibrated spectrum centered on the Hα emission. Bottom panel: observed Hα emission line profile of BOSS-EUVLG1, together with the two-components Gaussian fit and its residuals. Gray line: 1D observed Hα spectrum. Black line: best two-component Gaussian Hα fitted model. Red and blue lines: narrow and broad Hα components. Green line: [N II]6548,6583 Å lines. Gray dotted line: illustration of observed spectral line-spread function, derived from a sky line at 2.25 μm, normalized to the peak of the Hα emission, and centered within a velocity of −1200 km s⁻¹. The χ², calculated from −1000 to 750 km s⁻¹, is also included.