Map of the 339 GHz continuum emission of PKS 1830−211 showing the two resolved lensed images of the blazar (left). Overview of the ArH⁺ absorption spectrum toward PKS 1830−211 SW (bottom right) and NE (top right) from the current observations. Expected positions of the main absorption feature are indicated for ³⁶ArH⁺, ³⁸ArH⁺, and ⁴⁰ArH⁺; the last is not detected. The noise increases toward lower frequencies because of the proximity of the atmospheric water line near 325.2 GHz.

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).