2012ApJ...753..102W

We report on sensitive observations of the CO(J = 7 -> 6) and C I(³ P₂ -> ³ P₁) transitions in the z = 2.79 QSO host galaxy RXJ0911.4+0551 using the IRAM Plateau de Bure interferometer. Our extremely high signal-to-noise spectra combined with the narrow CO line width of this source (FWHM = 120 km/s) allows us to estimate sensitive limits on the spacetime variations of the fundamental constants using two emission lines. Our observations show that the C I and CO line shapes are in good agreement with each other but that the C I line profile is of the order of 10% narrower, presumably due to the lower opacity in the latter line. Both lines show faint wings with velocities up to ±250 km/s, indicative of a molecular outflow. As such, the data provide direct evidence for negative feedback in the molecular gas phase at high redshift. Our observations allow us to determine the observed frequencies of both transitions with so far unmatched accuracy at high redshift. The redshift difference between the CO and C I lines is sensitive to variations of ΔF/F with F = α²/µ where α is the fine structure constant and µ is the electron-to-proton mass ratio. We find ΔF/F = (6.9±3.7)x10^–6 at a look-back time of 11.3 Gyr, which, within the uncertainties, is consistent with no variations of the fundamental constants.