Constraining Changes In The Proton-electron Mass Ratio With Inversion And Rotational Lines

Abstract

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 [Δμ/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 (≥3σ) evidence for changes in μ, and obtain the stringent 3σ constraint, [Δμ/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.