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

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: [kmenten;rguesten;sthorwirth;chenkel;bklein]@mpifr-bonn.mpg.de
² ESO, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany e-mail: sleurini@eso.org
³ National Radio Astronomy Observatory, PO Box 0, Socorro, NM 87801-0387, USA e-mail: ccarilli@nrao.edu
⁴ Harvard-Smithsonian Center for Astrophysics 60 Garden Street Cambridge, MA 02138, USA e-mail: reid@cfa.harvard.edu

Received: 24 April 2008
Accepted: 15 October 2008

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.