Submillimeter water and ammonia absorption by the peculiar z ≈ 0.89 interstellar medium in the gravitational lens of the PKS 1830-211 system

Abstract

Using the Atacama Pathfinder Experiment (APEX) telescope, we have detected the rotational ground-state transitions of ortho-ammonia 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 in the proton to electron mass ratio over the past 7.2 Gyr. © 2008 ESO.