Radial profiles of HI (left) and MgII (right) column densities, averaging over annuli of thickness 0.5 kpc. The solid line represents the median value, and the shaded region includes the variation from the 10th to the 90th percentile. The observational data from the COS-Halos survey are overplotted, distinguishing between star-forming (blue squares) and non-star-forming (red diamonds) galaxies. The arrows indicate upper and lower limits.