Carbonates and ices in the \(z=0.89\) galaxy-absorber towards PKS 1830-211 and within star-forming regions of the Milky Way

A pair of 6.0 and 6.9 \(\mu\)m absorption features are frequently observed in Milky-Way (MW) molecular-clouds and YSOs; they also occur in the \(z=0.886\) rest-frame of a molecule-rich spiral galaxy obscuring blazar PKS 1830-211. I calibrate \(\chi^2\)-fitting methods which match observations with two or three laboratory spectra. The 6.0-\(\mu\)m component is dominated by H\(_2\)O ice, as expected. Included MW sources were selected using opacity criteria which limit the range of explored H\(_2\)O-ice column densities to 1.6--\(2.4 \times 10^{18}\) molecules cm\(^{-2}\), while the H\(_2\)O-ice density in the galaxy absorber is \((2.7\pm 0.5)\times 10^{18}\) molecules cm\(^{-2}\). CH\(_3\)OH ice and / or small (< 0.1-\(\mu\)m-sized) Ca- and Mg-bearing carbonates contribute at 6.9 \(\mu\)m. The 41 % CH\(_3\)OH : H\(_2\)O molecular ratio in the PKS 1830-211 absorber is significantly higher than in the molecular cloud towards Taurus-Elias 16 (