Rest-frame absorption equivalent width |${W_{\rm r}(2796)}$| versus projected distance d for LRGs with sufficiently high S/N background QSO spectra for detecting Mg ii absorbers as weak as W₀ = 0.3 Å. Absorption observations for passive LRGs are shown in the left-hand panel. Observations of [O ii]-emitting LRGs are shown in the right-hand panel. LRGs with detected Mg ii absorbers are shown in filled circles with error bars representing measurement uncertainties. For non-detections, we use light grey circles to indicate the 2σ upper limits. Note that a significant fraction of the original SDSS LRG sample have poor-quality QSO spectra, which result in upper limits exceeding 0.3 Å. These LRG-QSO pairs offer few or no constraints for the underlying absorber strengths in LRG haloes and are therefore excluded from the plots for clarity.