Left panel: distribution of the centroid-velocity difference ΔV. Blue and yellow histograms represent the new TRAO sample and the PMO sample from Y. Wu et al. (2012), respectively. Solid curves show the best-fit Student’s t-distributions for the two full samples, with the corresponding fit parameters indicated. The dashed curve shows the fit for the TRAO subset associated with PGCCs exhibiting multiple detected ¹³CO velocity components. Right panel: comparison of the ¹²CO and ¹³CO centroid velocities for the same matched components. The solid line shows the linear fit to the TRAO data.