Constraining Fundamental Constant Evolution With H I and Oh Lines

We report deep Green Bank Telescope spectroscopy in the redshifted HI 21cm and OH 18cm lines from the $z = 0.765$ absorption system towards PMN J0134-0931. A comparison between the "satellite" OH 18cm line redshifts, or between the redshifts of the HI 21cm and "main" OH 18cm lines, is sensitive to changes in different combinations of three fundamental constants, the fine structure constant α, the proton-electron mass ratio μ ≡ mₚ/mₑ and the proton g-factor gₚ. We find that the satellite OH 18cm lines are not perfectly conjugate, with both different line shapes and stronger 1612 MHz absorption than 1720 MHz emission. This implies that the satellite lines of this absorber are not suitable to probe fundamental constant evolution. A comparison between the redshifts of the HI 21cm and OH 18cm lines, via a multi-Gaussian fit, yields the strong constraint [Δ F/F] = [-5.2 ± 4.3] × 10⁻⁶, where F ≡ gₚ [μ α²]1.57 and the error budget includes contributions from both statistical and systematic errors. We thus find no evidence for a change in the constants between $z = 0.765$ and the present epoch. Incorporating the constraint [Δ μ/μ ] < 3.6 × 10⁻⁷ from another absorber at a similar redshift and assuming that fractional changes in gₚ are much smaller than those in α, we obtain [Δ α/α ] = (-1.7 ± 1.4) × 10⁻⁶ over a lookback time of 6.7 Gyrs.