Constraining changes in the proton-electron mass ratio with inversion and rotational lines

Abstract

We report deep Green Bank Telescope spectroscopy in the redshifted NH 3 (1,1), CS 1-0, and H2CO 000-101 lines from the z ∼ 0.685 absorber toward 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 three-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, [Aμ/μ] < 3.6 × 10 -7, over 6.2 Gyr; this is the best present limit on temporal changes in μ from any technique, and for any look-back time, by a factor >5. © 2011. The American Astronomical Society. All rights reserved. Printed in the U.S.A.