Submillimeter water and ammonia absorption by the peculiar z ≈ 0 . 89 interstellar medium in the gravitational lens of the PKS 1830 − 211 system

Using the Atacama Pathfinder Experiment (APEX) telescope we have detected the rotational ground-state transitions of orthoammonia and ortho-water toward the redshift ≈ 0.89 absorbing galaxy in the PKS 1830−211 gravitational lens system. We discuss our observations in the context of recent space-borne data obtained for these lines with the SWAS and Odin satellites toward Galactic sources. We find commonalities, but also significant differences between the interstellar media in a galaxy at intermediate redshift and in the Milky Way. Future high-quality observations of the ground-state ammonia transition in PKS 1830−211, together with inversion line data, will lead to strong constraints on the variation of the proton to electron mass ratio over the past 7.2 Gyr.