Detection of chloronium and measurement of the ³⁵Cl/³⁷Cl isotopic ratio at z = 0.89 toward PKS 1830–211

¹ Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, 43992 Onsala, Sweden
e-mail: mullers@chalmers.se
² Institut de Radioastronomie Millimétrique, 300 rue de la piscine, 38406 St-Martin d’Hères, France
³ LRA/LERMA, CNRS UMR 8112, Observatoire de Paris & École Normale Supérieure, 75231 Paris, France
⁴ Max-Planck-Institut für Radioastonomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁵ Astron. Dept., King Abdulaziz University, PO Box 80203, 21589 Jeddah, Saudi Arabia
⁶ Observatoire de Paris, LERMA, CNRS, 61 Av. de l’Observatoire, 75014 Paris, France
⁷ Institut d’Astrophysique Spatiale, Bât. 121, Université Paris-Sud, 91405 Orsay Cedex, France
⁸ Center for Astrophysics and Space Astronomy, Department of Astrophysical and Planetary Sciences, University of Colorado, 389 UCB, Boulder, CO 80309-0389, USA
⁹ Institute of Physics, Vietnam Academy of Science and Technology, 10 DaoTan, ThuLe, BaDinh, Hanoi, Vietnam
¹⁰ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching b. München, Germany

Received: 4 April 2014
Accepted: 28 April 2014

Abstract

We report the first extragalactic detection of chloronium (H₂Cl⁺) in the z = 0.89 absorber in front of the lensed blazar PKS 1830−211. The ion is detected through its 1₁₁-0₀₀ line along two independent lines of sight toward the North-East and South-West images of the blazar. The relative abundance of H₂Cl⁺ is significantly higher (by a factor ~7) in the NE line of sight, which has a lower H₂/H fraction, indicating that H₂Cl⁺ preferably traces the diffuse gas component. From the ratio of the H₂³⁵Cl⁺ and H₂³⁷Cl⁺ absorptions toward the SW image, we measure a ³⁵Cl/³⁷Cl isotopic ratio of 3.1_-0.2^+0.3 at z = 0.89, similar to that observed in the Galaxy and the solar system.