Constraints on changes in the proton–electron mass ratio using methanol lines

2014/12/24 by Nissim Kanekar, N. Kanekar, W. Ubachs +10 · 58 citations
Physics and Astronomy · #Advanced Frequency and Time Standards #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Electron #Emission spectrum #Galaxy #Line (geometry) #Mass ratio #Nuclear physics #Physics #Proton #Redshift #Sensitivity (control systems) #Spectral line #Stellar, planetary, and galactic studies #astro-ph.CO #astro-ph.GA

paper · pdf · doi:10.1093/mnrasl/slu206

published in Monthly Notices of the Royal Astronomical Society Letters 448(1), L104-L108 (Oxford University Press) · 6 pages, 1 figure; accepted for publication in MNRAS Letters

arxiv created 2014/12/24 · openalex publication_date 2015/02/09 · arxiv updated 2015/06/23 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05

Abstract

Abstract We report Karl G. Jansky Very Large Array (VLA) absorption spectroscopy in four methanol (CH3OH) lines in the z = 0.885 82 gravitational lens towards PKS1830−211. Three of the four lines have very different sensitivity coefficients Kμ to changes in the proton–electron mass ratio μ; a comparison between the line redshifts thus allows us to test for temporal evolution in μ. We obtain a stringent statistical constraint on changes in μ by comparing the redshifted 12.179 and 60.531 GHz lines, [Δμ/μ] ≤ 1.1 × 10−7 (2σ) over 0 < z ≤ 0.885 82, a factor of ≈2.5 more sensitive than the best earlier results. However, the higher signal-to-noise ratio (by a factor of ≈2) of the VLA spectrum in the 12.179 GHz transition also indicates that this line has a different shape from that of the other three CH3OH lines (at >4σ significance). The sensitivity of the above result, and that of all earlier CH3OH studies, is thus likely to be limited by unknown systematic errors, probably arising due to the frequency-dependent structure of PKS1830−211. A robust result is obtained by combining the three lines at similar frequencies, 48.372, 48.377 and 60.531 GHz, whose line profiles are found to be in good agreement. This yields the 2σ constraint [Δμ/μ] ≲ 4 × 10−7, the most stringent current constraint on changes in μ. We thus find no evidence for changes in the proton–electron mass ratio over a lookback time of ≈7.5 Gyr.

Citations

• Frequency Ratio of Al+and Hg+Single-Ion Optical Clocks; Metrology at the 17th Decimal Place
• Methods for Constraining Fine Structure Constant Evolution with OH Microwave Transitions
• Changes in the measured image separation of the gravitational lens system PKS 1830-211
• Probing isotopic ratios atz= 0.89: molecular line absorption in front of the quasar PKS 1830-211
• Varying constants, Gravitation and Cosmology
• Limit on the Present Temporal Variation of the Fine Structure Constant
• Time variability of α from realistic models of Oklo reactors
• A Stringent Limit on a Drifting Proton-to-Electron Mass Ratio from Alcohol in the Early Universe

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