Surface density maps for all Class I and II candidates classified using the four IRAC flux criteria in Sect. 3.2 (left) and candidates taken from the WISE catalog from Marton et al. (2016) (center). The spatial scales of the maps are normalized by the bubble radius (solid black circle). The dashed black circle represents the average shell radius (R_shell = 1.85 × R_eff). The mean radial source density profiles (right) for the IRAC YSO candidates (solid black) and WISE YSO candidates (solid red) are shown as a function of distance to the central position of the H ii regions, obtained by azimuthally averaging from the surface density maps.