Abstract
We report the detection of OH+ and H2O+ in the z = 0.89 absorber toward the lensed quasar PKS 1830-211. The abundance ratio of OH+ and H2O+ is used to quantify the molecular hydrogen fraction (f(H2)) and the cosmic-ray ionization rate of atomic hydrogen (zeta(H)) along two lines of sight, located at similar to 2 kpc and similar to 4 kpc to either side of the absorber's center. The molecular fraction decreases outward, from similar to 0.04 to similar to 0.02, comparable to values measured in the Milky Way at similar galactocentric radii. For zeta(H), we find values of similar to 2 x 10(-14) s(-1) and similar to 3 x 10(-15) s(-1), respectively, which are slightly higher than in the Milky Way at comparable galactocentric radii, possibly due to a higher average star formation activity in the z = 0.89 absorber. The ALMA observations of OH+, H2O+, and other hydrides toward PKS 1830-211 reveal the multi-phase composition of the absorbing gas. Taking the column density ratios along the southwest and northeast lines of sight as a proxy of molecular fraction, we classify the species ArH+, OH+, H2Cl+, H2O+, CH, and HF as tracing gases increasingly more molecular. Incidentally, our data allow us to improve the accuracy of H2O+ rest frequencies and thus refine the spectroscopic parameters.