Normalized GTC spectra of the 13 UV-bright galaxies studied in this work around the He IIλ1640 line (black, and 1σ uncertainty in gray). Spectra are normalized using the continuum regions marked in red. Equivalent widths of the He II line are measured by integrating the spectral regions from 1630 Å to 1655 Å (blue regions). Green dashed lines show Gaussian fits of the He IIλ1640 emission. The x-axes represent the rest-frame and observed wavelengths (bottom and top axis, respectively).