Comparison of the observed width of the ammonia line for a sample of low-mass pre-stellar cores collected by Jijina et al. (1999) (green), width of the C¹⁸O J = 3–2 spectra (blue) and C¹⁸O J = 9–8 line widths (red) for the detected WISH sample of low-mass protostars (top). The histogram of the bottom presents the same values but for high-mass pre-stellar cores and the WISH high-mass sample of YSOs.