|
Description
Molecular hydrogen in the interstellar medium (ISM) of high-redshift galaxies can be detected directly from its UV absorptions imprinted in the spectrum of background quasars. Associated absorptions from HI and metals allow for the study of the chemical enrichment of the gas, while the analysis of excited species and molecules make it possible to infer the physical state of the ISM gas. In addition, given the numerous H_2_ lines usually detected, these absorption systems are unique tools to constrain the cosmological variation of the proton-to-electron mass ratio, {mu}. We intend to study the chemical and physical state of the gas in the H_2_-bearing cloud at z_abs_=2.658601 towards the quasar QJ0643-5041 (z_em_=3.09) and to derive a useful constraint on the variation of {mu}. We use high signal-to-noise ratio, high-resolution VLT-UVES data of QJ0643-5041 amounting to a total of more than 23 hours exposure time and fit the HI, metals, and H_2_ absorption features with multiple-component Voigt profiles. We study the relative populations of H_2_ rotational levels and the fine-structure excitation of neutral carbon to determine the physical conditions in the H_2_-bearing cloud.
|
