Completeness curve f_C(log F [erg s⁻¹ cm⁻² Å⁻¹]) from a fake source insertion and recovery experiment on the MUSE HDF-S datacube at 5000 Å. The dotted vertical line shows the 50% completeness limit at log F [erg s⁻¹ cm⁻²]= − 17.75 and the dashed vertical line shows the analytically approximated minimum line flux given in Eq. (2) as log F_line [erg s⁻¹ cm⁻²] ≈ − 17.69 at which LSDCat is expected to detect emission line sources in this experiment.