Neutral chlorine and molecular hydrogen at high redshift

Abstract

Chlorine and molecular hydrogen are known to be tightly linked together in the cold phase of the local interstellar medium through rapid chemical reactions. We present here the first systematic study of this relation at high redshifts using H2-bearing damped Lya systems (DLAs) detected along quasar lines of sight. Using high-resolution spectroscopic data from VLT/UVES and Keck/HIRES, we report the detection of Cli in 9 DLAs (including five new detections) out of 18 high-z DLAs with N(H2) = 1017.3 cm-2 (including a new H2 detection at z = 3.09145 towards J 2100-0641) and present upper limits for the remaining 9 systems. We find a ~5s correlation between N(Cli) and N(H2) with only ~0.2 dex dispersion over the range 18.1.