Indications of electron-to-proton mass ratio variations in the Galaxy. III. 0.6mm methanol lines toward SgrB2(N) and Orion-KL

Abstract

In this paper, we show that methanol (CH3OH) torsional-rotational transitions, which have increased sensitivity to small variations of mu - the electron-to-proton mass ratio, are shifted relative to less sensitive transitions in the spectrum of the SgrB2(N) molecular cloud located at the Galactic center. At the same time, an identical set of methanol lines in the spectrum of the Orion-KL molecular cloud, located far from the center, shows no shifts. Interpreting this behavior of molecular frequencies in terms of Delta mu/mu = (mu_obs - mu_lab)/mu_lab leads to the following weighted mean values: <Delta mu/mu> = (-3.4 +/- 0.4)*10^(-7) for SgrB2 and <Delta mu/mu> = (-1.1 +/- 0.8)*10^(-7) for Orion-KL (indicated are the total +/-1sigma errors of the weighted means <Delta mu/mu> including both statistical and systematic uncertainties). A possible correlation between <Delta mu/mu> values measured in various molecular clouds of the Galactic disk and the distribution of dark matter along the Galactic radius is discussed, which may suggest a hypothetical modulation of the Higgs scalar field by dark matter, resulting in a change of mu.

Figures (3)

• Figure 1: The methanol (CH$_3$OH) lines toward two sources -- Sgr B2(N) and Orion-KL, obtained at the space observatory Herschel. The original spectra are shown in black and the model spectra -- in red. The numbers next to the lines indicate laboratory frequencies $f_{\rm lab}$ in GHz (see Table \ref{['Tab2']}).
• Figure 2: ( Top panel.) Map of normalized minimum values of $\chi^2_{\rm min}$ as a function of gas density $n(H_2)$ and kinetic temperature $T_{\rm kin}$ at different values of column densities $N_{\rm A}$ and $N_{\rm E}$. Vertical dotted lines limit the range of acceptable values of A/E. The point is marked with a star {$n(H_2), T_{\rm kin}, N_{\rm A}, N_{\rm E}$} = {1.5e7, 85, 1.96e15, 1.86e15}. ( Bottom panel.) Example of calculated and observed peak temperatures (red and black, respectively) for the thirteen methanol lines from Table \ref{['Tab3']} at the point marked with the star in the upper panel. The minimum values of $\chi^2$ at this point are as follows: $\chi^2_{\rm A} =0.7$, $\chi^2_{\rm E}=0.8$, and $\chi^2_{\rm A+E} = 0.7$.
• Figure 3: Measured values of $\Delta\mu/\mu$ along the galactocentric radius $R_{\rm GC}$, normalized to the effective Galactic radius $R_{\rm eff} \approx 4.5$ kpc. The points with uncertainty intervals $\pm1\sigma$ are taken from the following publications: a --L22, b -- this work, c --Dap, d --VKL24VL24 and e --VLK26, in which the values of $\Delta\mu/\mu$ were estimated along the lines CH$_3$OH (the first three links), $^{13}$CH$_3$OH (the next two links) and CH$_3$CHO (the last link). The regression line (pink) is surrounded by the confidence zones $\pm1\sigma$ (light gray) and $\pm3\sigma$ (dark gray).