Robust constraint on a drifting proton-to-electron mass ratio at z=0.89 from methanol observation at three radio telescopes

Abstract

A limit on a possible cosmological variation of the proton-to-electron mass ratio μ is derived from methanol (CH3OH) absorption lines in the benchmark PKS1830-211 lensing galaxy at redshift z=0.89 observed with the Effelsberg 100-m radio telescope, the Institute de Radio Astronomie Millimétrique 30-m telescope, and the Atacama Large Millimeter/ submillimeter Array. Ten different absorption lines of CH3OH covering a wide range of sensitivity coefficients Kμ are used to derive a purely statistical 1σ constraint of Δμ/μ=(1.5±1.5) ×10-7 for a lookback time of 7.5 billion years. Systematic effects of chemical segregation, excitation temperature, frequency dependence, and time variability of the background source are quantified. A multidimensional linear regression analysis leads to a robust constraint of Δμ/μ=(- 1.0±0.8stat±1.0sys)×10-7. © 2013 American Physical Society.