First cosmological constraints on the proton-to-electron mass ratio from observations of rotational transitions of methanol

TL;DR

This study uses methanol absorption lines observed with the Australia Telescope to place constraints on the variation of the proton-to-electron mass ratio over cosmic time, achieving high precision and suggesting potential for future improvements.

Contribution

First to constrain the proton-to-electron mass ratio at z=0.89 using methanol rotational transitions with high precision.

Findings

Constraint on proton-to-electron mass ratio change: 0.8 +/- 2.1 x 10^-7.

Comparable precision to recent z=0.68 studies.

Potential to improve constraints by a factor of 5-10 with future observations.

Abstract

We have used the Australia Telescope Compact Array to measure the absorption from the 2(0) - 3(-1}E 12.2 GHz transition of methanol towards the z=0.89 lensing galaxy in the PKS B 1830-211 gravitational lens system. Comparison of the velocity of the main absorption feature with the published absorption spectrum from the 1(0) - 2(-1)E transition of methanol shows that they differ by -0.6 +/- 1.6 km/s . We can use these observations to constrain the changes in the proton-to-electron mass ratio from z=0.89 to the present to 0.8 +/- 2.1 x 10^-7. This result is consistent, and of similar precision to recent observations at z = 0.68 achieved through comparison of a variety of rotational and inversion transitions, and approximately a factor of 2 better than previous constraints obtained in this source. Future more sensitive observations which incorporate additional rotational methanol transitions offer the prospect of improving current results by a factor of 5-10.