Analysis of carbon monoxide absorption at zabs ≃ 2.5 to constrain variation of the proton-to-electron mass ratio

Absorption by carbon monoxide in the spectrum of quasar SDSS J000015.16+004833.2 is investigated in order to derive a constraint on the temporal variation of the proton-to-electron mass ratio, μ. The spectrum was recorded using Very Large Telescope/Ultraviolet and Visual Echelle Spectrograph, and it was partially corrected for long-range wavelength scale distortions using the supercalibration technique. Eight vibrational CO singlet-singlet bands belonging to the A¹Π-X¹Σ⁺ electronic absorption system, and the perturbing d³Δ-X¹Σ⁺(5, 0) singlet-triplet band are detected in the damped Lyman α system at z_abs ≃ 2.52. The spectra are modelled using a comprehensive fitting technique, resulting in a final value of Δμ/μ = (1.8 ± 2.2_stat ± 0.4_syst) × 10^-5, which is consistent with no variation over a look-back time of ∼11.2 Gyr.