First panel: average surface mass stellar density profiles obtained from the stacking of 3.6 μm I₀ profiles, resized to a common physical scale in kpc, of 79 disk galaxies with total stellar masses comparable (± 0.1 dex) to that of the Milky Way (M_MW ≈ 5 × 10¹⁰M_⊙). Different ways of averaging the stacks are compared, as indicated in the upper right legend. The sample dispersion (σ) and the standard deviation of the mean (σ/) are indicated with error bars (dashed and solid vertical lines, respectively), centred on the mean profile stacked in units of mag. The median profile for MW galaxies at z ≈ 0 from van Dokkum et al. (2013, traced from their Fig. 3) is also overplotted. Second panel: for the same MW-type stellar mass bin, the fraction of galaxies whose radial profile extends to a given galactocentric radius. The 75%, 50%, and 25% sample completeness levels are highlighted with vertical solid, dashed, and dotted lines, respectively. Third panel: mean Σ_∗ of MW galaxies sampled based on how far they extend (estimated from R_lim) relative to R_25.5. Fourth panel: for the systems in our sample, histogram of the distributions of the image outer radius relative to R_25.5.