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

Abstract

We report the first extragalactic detection of chloronium (H 2Cl+) in the z = 0.89 absorber in front of the lensed blazar PKS 1830-211. The ion is detected through its 111-0 00 line along two independent lines of sight toward the North-East and South-West images of the blazar. The relative abundance of H 2Cl+ 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. © 2014 ESO.