2017MNRAS.471.2143L

The offsets between the radial velocities of the rotational transitions of carbon monoxide and the fine structure transitions of neutral and singly ionized carbon are used to test the hypothetical variation of the fine structure constant, α. From the analysis of the [C I] and [C II] fine structure lines and low J rotational lines of ¹²CO and ¹³CO, emitted by the dark cloud L1599B in the Milky Way disc, we find no evidence for fractional changes in α at the level of |Δα/α| < 3 x 10^–7. For the neighbouring galaxy, M33, a stringent limit on Δα/α is set from observations of three H II zones in [C II] and CO emission lines: |Δα/α| < 4 x 10^–7. Five systems over the redshift interval z = 5.7-6.4, showing CO J = 6-5, J = 7-6 and [C II] 158 µm emission, yield a limit on |Δα/α| < 1.3 x 10^–5. Thus, a combination of the [C I], [C II] and CO emission lines turns out to be a powerful tool for probing the stability of the fundamental physical constants over a wide range of redshifts not accessible to optical spectral measurements.