Probing the electron-to-proton mass ratio gradient in the Milky Way with Class I methanol masers
Journal article, 2022
We estimate limits on non-universal coupling of hypothetical hidden fields to standard matter by evaluating the fractional changes in the electron-to-proton mass ratio, mu = m(e)/m(p), based on observations of Class I methanol masers distributed in the Milky Way disc over the range of the Galactocentric distances 4 less than or similar to R less than or similar to 12 kpc. The velocity offsets Delta V = V-44 - V-95 measured between the 44- and 95-GHz methanol lines provide, so far, one of the most stringent constraints on the spatial gradient k(mu)= d(Delta mu/mu)/dR < 2 x10(-9) kpc(-1) and the upper limit on Delta mu/mu <2 x 10(-8), where Delta mu/mu = (mu(obs) - mu(lab))/mu(lab). We also find that the offsets Delta V are clustered into two groups which are separated by delta(Delta V) = 0.022 +/- 0.003 km s(-1) (1 sigma confidence level). The grouping is most probably due to the dominance of different hyperfine transitions in the 44- and 95-GHz methanol maser emission. Which transition becomes favoured is determined by an alignment (polarization) of the nuclear spins of the four hydrogen atoms in the methanol molecule. This result confirms that there are preferred hyperfine transitions involved in the methanol maser action.
elementary particles
methods: observational
ISM: molecules
techniques: spectroscopic
masers
Author
S. A. Levshakov
Saint Petersburg Electrotechnical University
National Research Centre "Kurchatov Institute"
Russian Academy of Sciences
I. I. Agafonova
Saint Petersburg Electrotechnical University
C. Henkel
Chinese Academy of Sciences
Max Planck Society
King Abdulaziz University
Kee-Tae Kim
University of Science and Technology (UST)
Korea Astronomy and Space Science Institute
M. G. Kozlov
Saint Petersburg Electrotechnical University
National Research Centre "Kurchatov Institute"
Boy Lankhaar
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
W. Yang
Max Planck Society
Monthly Notices of the Royal Astronomical Society
0035-8711 (ISSN) 1365-2966 (eISSN)
Vol. 511 1 413-424Subject Categories
Subatomic Physics
Astronomy, Astrophysics and Cosmology
Theoretical Chemistry
DOI
10.1093/mnras/stac024