2016ApJ...826..192D

Carbon monoxide (CO) absorption in the sub-damped Lyα absorber at redshift {z}_abs≃2.69 toward the background quasar SDSS J123714.60+064759.5 (J1237+0647) was investigated for the first time in order to search for a possible variation of the proton-to-electron mass ratio, µ, over a cosmological timescale. The observations were performed with the Very Large Telescope/Ultraviolet and Visual Echelle Spectrograph with a signal-to-noise ratio of 40 per 2.5 km/s per pixel at ∼5000 Å. Thirteen CO vibrational bands in this absorber are detected: the {A}^{1}Π - {X}^{1}{Σ}^+ ( ν^′ , 0) for ν^′ =0–8 , {B}^{1}{Σ}^+ - {X}^{1}{Σ}^+ (0, 0), {C}^{1}{Σ}^+ - {X}^{1}{Σ}^+ (0, 0), and {E}^{1}Π - {X}^{1}{Σ}^+ (0, 0) singlet-singlet bands and the °^{3}Δ - {X}^{1}{Σ}^+ (5, 0) singlet-triplet band. An updated database including the most precise molecular inputs needed for a µ-variation analysis is presented for rotational levels J=0-5, consisting of transition wavelengths, oscillator strengths, natural lifetime damping parameters, and sensitivity coefficients to a variation of the proton-to-electron mass ratio. A comprehensive fitting method was used to fit all the CO bands at once and an independent constraint of Δµ/µ=(0.7±{1.6}_stat±{0.5}_syst)×{10}^{-5} was derived from CO only. A combined analysis using both molecular hydrogen and CO in the same J1237+0647 absorber returned a final constraint on the relative variation of Δµ/µ=(-5.6±{5.6}_stat±{3.1}_syst)×{10}^{-6} , which is consistent with no variation over a look-back time of ∼11.4 Gyr.