Chlorine-bearing molecules in molecular absorbers at intermediate redshifts^⋆

¹ Institute of Astronomy, KU Leuven, Celestijnenlaan 200D bus 2401, 3001 Leuven, Belgium
e-mail: shj.wallstrom@gmail.com
² Institute of Astronomy and Astrophysics, Academia Sinica, 11F of Astronomy-Mathematics Building, No.1, Sec. 4, Roosevelt Rd., 10617 Taipei, Taiwan
³ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 43992 Onsala, Sweden
⁴ LERMA/LRA, Ecole Normale Supérieure, Observatoire de Paris, CNRS UMR 8112, PSL Research University, Sorbonne Universités, UPMC Université Paris, 24 Rue Lhomond, 75005 Paris, France
⁵ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

Received: 9 May 2019
Accepted: 30 July 2019

Abstract

We use observations of chlorine-bearing species in molecular absorbers at intermediate redshifts to investigate chemical properties and ³⁵Cl/³⁷Cl isotopic ratios in the absorbing sightlines. Chloronium (H₂Cl⁺) is detected along three independent lines of sight in the z = 0.89 and z = 0.68 molecular absorbers located in front of the lensed quasars PKS 1830−211 and B 0218+357, respectively. Hydrogen chloride (HCl) was observed only toward PKS 1830−211, and is found to behave differently from H₂Cl⁺. It is detected in one line of sight with an abundance ratio [H₂Cl⁺] / [HCl] ∼1, but remains undetected in the other, more diffuse, line of sight, with a ratio [H₂Cl⁺] / [HCl] > 17. The absorption profiles of these two chlorine-bearing species are compared to other species and discussed in terms of the physical properties of the absorbing gas. Our findings are consistent with the picture emerging from chemical models where different species trace gas with different molecular hydrogen fraction. The ³⁵Cl/³⁷Cl isotopic ratios are measured in the different lines of sight and are discussed in terms of stellar nucleosynthesis.