Top panel: He II λ1640 flux as a function of redshift. He II λ1640 detections from MUSE are shown as stars and are colour-coded depending on their median continuum flux at ∼1640 Å. He II λ1640 detections from other surveys within the plot range are shown by diamonds. The redshift-dependent MUSE wavelength coverage of a few prominent rest-UV features are shown at the top of the panel. Bottom panel: M₁₅₀₀ as a function of redshift for the MUSE He II λ1640 detected and He II λ1640 non-detected galaxies (set B, see Sect. 3.2).