We report deep Green Bank Telescope (GBT) spectroscopy in the redshifted NH₃~(1,1), CS~1-0 and H₂CO~0₀₀-1₀₁ lines from the z ~ 0.685 absorber towards B0218+357. The inversion (NH₃) and rotational (CS, H₂CO) line frequencies have different dependences on the proton-electron mass ratio μ, implying that a comparison between the line redshifts is sensitive to changes in μ. A joint 3-component fit to the NH₃, CS, and H₂CO lines yields [Δ μ/μ] = (-3.5 ± 1.2) × 10⁻⁷, from z ~ 0.685 to today, where the error includes systematic effects from comparing lines from different species and possible frequency-dependent source morphology. Two additional sources of systematic error remain, due to time variability in the source morphology and velocity offsets between nitrogen-bearing and carbon-bearing species. We find no statistically-significant (≥ 3 σ) evidence for changes in μ, and obtain the stringent 3σ constraint, [Δ μ/μ] < 3.6 × 10⁻⁷, over 6.2~Gyrs; this is the best present limit on temporal changes in μ from any technique, and for any lookback time, by a factor 5.
No takes yet. Share an insight, caveat, or question.
Nissim Kanekar (2011) studied this question.