Detection of extragalactic argonium, ArH+, toward PKS 1830-211
Artikel i vetenskaplig tidskrift, 2015

Context. Argonium has recently been detected as a ubiquitous molecule in our Galaxy. Model calculations indicate that its abundance peaks at molecular fractions in the range of 10-4 to 10-3 and that the observed column densities require high values of the cosmic ray ionization rate. Therefore, this molecular cation may serve as an excellent tracer of the very diffuse interstellar medium (ISM), as well as an indicator of the cosmic ray ionization rate. Aims. We attempted to detect ArH+ in extragalactic sources to evaluate its diagnostic power as a tracer of the almost purely atomic ISM in distant galaxies. Methods. We obtained ALMA observations of a foreground galaxy at z = 0.89 in the direction of the lensed blazar PKS 1830−211. Results. Two isotopologs of argonium, 36ArH+ and 38ArH+, were detected in absorption along two different lines of sight toward PKS 1830−211, known as the SW and NE images of the background blazar. The argonium absorption is clearly enhanced on the more diffuse line of sight (NE) compared to other molecular species. The isotopic ratio 36Ar/38Ar is 3.46 ± 0.16 toward the SW image, i.e., significantly lower than the solar value of 5.5. Conclusions. Our results demonstrate the suitability of argonium as a tracer of the almost purely atomic, diffuse ISM in high-redshift sources. The evolution of the isotopic ratio with redshift may help to constrain nucleosynthetic scenarios in the early Universe.


abundances / astrochemistry / quasars: individual: PKS 1830-211

quasars: absorption lines / galaxies: ISM / galaxies: abundances / nuclear reactions


Holger Muller

Universität zu Köln

Sebastien Muller

Chalmers, Rymd- och geovetenskap, Onsala rymdobservatorium

P. Schilke

Universität zu Köln

E. A. Bergin

University of Michigan

John H Black

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

M. Gerin

LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres

D. Lis


LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres

D. A. Neufeld

Johns Hopkins University

Sümeyye Suri

Universität zu Köln

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 582 4- L4


Astronomi, astrofysik och kosmologi


Onsala rymdobservatorium