H₂/HD molecular data for analysis of quasar spectra in search of varying constants^⋆

¹ Department of Physics and Astronomy, Vrije Universiteit, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands
e-mail: w.m.g.ubachs@vu.nl
² Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Melbourne, 3122 Victoria, Australia
³ Sorbonne Université, Observatoire de Paris, Université PSL, CNRS, LERMA, 92190 Meudon, France

Received: 5 December 2018
Accepted: 24 December 2018

Abstract

Context. Absorption lines of H₂ 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 H₂ and HD absorption lines in the Lyman (B¹Σ_u⁺ − X¹Σ_g⁺) and Werner (C¹Π_u − X¹Σ_g⁺) band systems up to the Lyman cutoff at 912 Å. 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 H₂ 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.