Relative line contribution to the total flux (left) and fraction of channels that contain molecular emission (right) as a function of the continuum level obtained for the 1.3 mm bands. Red dots represent high-mass cores with M > 10 M_⊙, grey dots represent the other cores. The blue areas represent the results for spectra without many lines above the 1σ, 2σ, and 3σ levels, where σ is the rms noise level in one channel of the corresponding band. Cores identified as containing a hot core following the criterion described in Sect. 1 are marked by their core number.