Normalised first two modes derived by the PCA analysis performed on the original footprint OF (solid blue line) and the conservative footprint CF (solid orange), and their weighted version ‘OFw’ (solid green) and ‘CFw’ (red dashed). For comparison, in the first mode plot (top panel), we show a proxy for the spectral index of the galactic free-free emission (dash-dotted, spectral index of −2.13, Dickinson et al. 2003) and a range of possible galactic synchrotron spectral indexes (blue shaded area, between −3.2 and −2.6, Irfan et al. 2022).