Detection of extragalactic argonium, ArH+, toward PKS 1830-211
Journal article, 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.

nucleosynthesis

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

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

Author

Holger Muller

University of Cologne

Sebastien Muller

Chalmers, Earth and Space Sciences, Onsala Space Observatory

P. Schilke

University of Cologne

E. A. Bergin

University of Michigan

John H Black

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

M. Gerin

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

D. Lis

California Institute of Technology (Caltech)

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

D. A. Neufeld

Johns Hopkins University

Sümeyye Suri

University of Cologne

Astronomy and Astrophysics

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

Vol. 582 4- L4

Subject Categories

Astronomy, Astrophysics and Cosmology

Infrastructure

Onsala Space Observatory

DOI

10.1051/0004-6361/201527254

More information

Latest update

4/20/2018