Fine-structure transitions as a tool for studying variation of α at high redshifts

Abstract Star-forming galaxies at high redshifts are the ideal targets to probe the hypothetical variation of the fine-structure (FS) constant α over cosmological time-scales. We propose a modification of the alkali doublets method that allows us to search for variation in α combining far-infrared and submillimetre spectroscopic observations. This variation manifests as velocity offsets between the observed positions of the FS and gross-structure transitions when compared to laboratory wavelengths. Here we describe our method whose sensitivity limit to the fractional changes in α is about 5 × 10−7. We also demonstrate that current spectral observations of hydrogen and C ii 158 μm lines provide an upper limit on |Δα/α| ≲ 6 × 10 − 5 at redshifts z = 3.1 and 4.7.