Correlation wheels, showing the initial line intensities as vectors having as coordinates their correlation coefficients to each PC, represented in the planes of successive pairs of PCs. Uncertainties from our bootstraping analysis (see Sect. 4.3) are presented as thin black contours around the arrows’ heads (isodensity contours containing 68% of the distribution). Also represented in colored arrows are the correlations of our independent physical parameters with the PCs (red: log N_H2, green: log n_H, blue: ).