Plot of average linewidth vs. core temperature. The BLAST-derived dust temperature has been used, except in those sources where T_k could be determined from NH₃ (see Sect. 3.3). In estimating the averages, only the linewidths of the optically thin molecular tracers (N₂H⁺, H¹³CO⁺ and H¹³CN) have been considered. As in Figs. 1 and 5 starless cores are represented by circles, but proto-stellar cores are shown by triangles (instead of crosses, for best use of the color code). The filling color code represents the relative abundance [HNC]/[HCN] (top panel) and [N₂H⁺]/[H¹³CO⁺] (bottom panel). The solid line represents the linear fit (from Bayesian statistics) to all points.