Distance bias. Panels a and b: δ values for the combination of S-type AS and NA, and the combination of O-type AS and NA HMSCs, respectively. All sources are grouped into three distance bins, which are <4 kpc, 4–8 kpc, and >8 kpc. Dots withdifferent colors mean different properties of HMSCs. The red, orange, and blue numbers in (b) are the numbers of S-type AS, O-type AS, and NA HMSCs in the corresponding distance ranges. The gray regions are |δ| ≤ 1, where we suggest that the differences are insignificant.