A new approach for testing variations of fundamental constants over cosmic epochs using FIR fine-structure lines

Aims. We aim to obtain limits on the variation of the fine-structure constant α and the electron-to-proton mass ratio μ over different cosmological epochs. Methods. A new approach based on the comparison of redshifts of far infrared (FIR) fine-structure lines and low-lying rotational transitions in CO is proposed which is in principle more sensitive by a factor of ~10 than QSO metal absorption lines. Results. Estimations of the quotient $F = \alpha^2/\mu$ obtained for two distant quasars J1148+5251 ( z = 6.42) and BR 1202–0725 ( z = 4.69) provide ${\Delta F}/{F}$ = (0.1 ± 1.0)$\times$10 -4 and (1.4 ± 1.5)$\times$10 -4 . The obtained limits are consistent with no variation of physical constants at the level of ~0.01% over a period of 13 Gyr. Conclusions. Upcoming observations of quasars and distant galaxies in FIR fine-structure lines of different species and in CO low rotational lines at the SOFIA, HSO, and ALMA are expected to improve the current limit by, at least, an order of magnitude.