2012ApJ...746L..16K

We report deep Green Bank Telescope spectroscopy in the redshifted H I 21 cm and OH 18 cm lines from the z = 0.765 absorption system toward PMN J0134-0931. A comparison between the "satellite" OH 18 cm line redshifts, or between the redshifts of the H I 21 cm and "main" OH 18 cm lines, is sensitive to changes in different combinations of three fundamental constants, the fine structure constant α, the proton-electron mass ratio µ ≡ m_p/m_e, and the proton g-factor g_p. We find that the satellite OH 18 cm 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 H I 21 cm and OH 18 cm lines, via a multi-Gaussian fit, yields the strong constraint [ΔF/F] = [ - 5.2 ±4.3]x10^–6, where F ≡ g_p[µα²]^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 [Δµ/µ] < 3.6x10^–7 from another absorber at a similar redshift and assuming that fractional changes in g_p are much smaller than those in α, we obtain [Δα/α] = (- 1.7±1.4)x10^–6 over a look-back time of 6.7 Gyr.