H$_2$/HD molecular data for analysis of quasar spectra in search of varying constants

Abstract

Absorption lines of H$_2$ and HD molecules observed at high redshift in the line of sight towards quasars are a test ground to search for variation of the proton-to-electron mass ratio $μ$. For this purpose, results from astronomical observations are compared with a compilation of molecular data of the highest accuracy, obtained in laboratory studies as well as in first-principles calculations. Aims: A comprehensive line list is compiled for H$_2$ and HD absorption lines in the Lyman ($B^1Σ_u^+$ - $X^1Σ_g^+$) and Werner ($C^1Π_u$ - $X^1Σ_g^+$) band systems up to the Lyman cutoff at 912 Angstroms. Molecular parameters listed for each line $i$ are the transition wavelength $λ_i$, the line oscillator strength $f_i$, the radiative damping parameter of the excited state $Γ_i$, and the sensitivity coefficient $K_i$ for a variation of the proton-to-electron mass ratio. Methods: The transition wavelengths $λ_i$ for the H$_2$ and HD molecules are determined by a variety of advanced high-precision spectroscopic experiments involving narrowband vacuum ultraviolet lasers, Fourier-transform spectrometers, and synchrotron radiation sources. Results for the line oscillator strengths $f_i$, damping parameters $Γ_i$, and sensitivity coefficients $K_i$ are obtained in theoretical quantum chemical calculations. Results: A new list of molecular data is compiled for future analyses of cold clouds of hydrogen absorbers, specifically for studies of $μ$-variation from quasar data. The list is applied in a refit of quasar absorption spectra of B0642$-$5038 and J1237$+$0647 yielding constraints on a variation of the proton-to-electron mass ratio $Δμ/μ$ consistent with previous analyses.

4 pages. Accepted by Astronomy and Astrophysics. The 3 tables containing the molecular data are available at http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=J/A+A/622/A127 and are contained in the source package of the arXiv submission (in "Other formats")