Detection of chloronium and measurement of the 35Cl/37Cl isotopic ratio at z=0.89 toward PKS1830-211

TL;DR

This study reports the first extragalactic detection of chloronium (H2Cl+) at z=0.89 and measures the 35Cl/37Cl isotopic ratio, providing insights into interstellar chemistry and isotopic compositions beyond the Milky Way.

Contribution

It presents the first detection of chloronium in an extragalactic environment and measures the isotopic ratio at high redshift, expanding understanding of interstellar molecules and isotopic variations.

Findings

Detected H2Cl+ in a galaxy at z=0.89

Measured 35Cl/37Cl ratio of approximately 3.1

H2Cl+ traces diffuse gas component

Abstract

We report the first extragalactic detection of chloronium (H2Cl+), in the z=0.89 absorber in front of the lensed blazar PKS1830-211. The ion is detected through its 1_11-0_00 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 H2^35Cl+ and H2^37Cl+ 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.