Cross-correlations of profiles from exposures with high signal levels. All lines are from the z_abs = 0.45207 system. Left upper panel: solid line – the normalized Mg ii λ2796 Å profile composed from 12 exposures with similar signal levels (100–150 counts per pixel at the continuum level); dotted line – the normalized Mg ii λ2796 Å profile from the exposure #2, setting 437 (Table 1) with a high level of signal (~500 counts per pixel). Left lower panel: as function of δv (same as in Fig. 1). The dotted line profile is to be shifted by  ≈  −250 m s^-1 to become fully aligned with the composite profile. Right upper panel: solid line – the normalized profile of the weak Ca i λ4227 Å line composed from eight exposures with similar signal (~300 counts per pixel); dotted line – the normalized Ca i λ4227 Å profile from the exposure #1, setting 760 (Table 1) with a high level of signal (~1000 counts per pixel). Right lower panel: as function of δv (same as in Fig. 1). The dotted line profile is distorted by noise, which leads to its apparent shift relative to the composite profile of about  −1000 m s^-1. The real shift of this portion of the exposure #1 is only  −150 m s^-1 as calculated from profiles of a strong Fe ii  λ2382 Å line at z_abs = 1.5864 located in the vicinity of Ca i λ4227 Å.