Single Voigt profile fit to the cold, narrow component at z = 0.45206 (ESPRESSO data: black with grey error bars, synthetic spectrum: red). Residuals (in units of standard deviation) are shown in the subpanel above each line panel. The zero of the velocity scale is taken at the velocity of the iron and calcium lines. The redshifts of the magnesium lines were left to vary independently from the other lines and are displayed as short red tick marks. The blue profiles and the corresponding blue tick marks and residuals correspond to the apparent velocity shift (−0.47 and −0.17 km s⁻¹ from Mg II and Mg I respectively) measured by Agafonova et al. (2011) from UVES data.