Normalized correlation plot of H₂O⁺ versus ³⁶ArH⁺ toward PKS 1830−211 SW, NE, and Sagittarius B2(M). The column densities of the two species have been normalized by the maximum values for each component and for each velocity channel. A perfect correlation (i.e. just a constant scaling factor between the two species) would result in clustering along the yellow line. The distributions of the two cations are poorly correlated toward the sources. The PKS 1830−211 data are from this work and from Muller et al. (in prep.) for ³⁶ArH⁺ and H₂O⁺, respectively; the corresponding Sagittarius B2(M) data are from Schilke et al. (2014) and Schilke et al. (2013).