Variations in galaxy number density n as a function of radial distance from the lens positions, using the X-ray peaks (diamonds) and BGG positions (squares). Data points are slightly offset for clarity. Overplotted is the average number density of ~64 galaxies/arcmin² of the whole ACS mosaic (black solid line) and the best-fit radial profile (dashed) with 1σ errors (dotted). The estimated effect of the lensing magnification, μ^α−1, is shown in grayscale, varying the slope of the luminosity function between 0 <α< 3. Different shades in grayscale correspond to steps of 0.5 × 10¹⁴ in group mass M₂₀₀.