2026ApJ...998..291Y

The magnitude gap between the central and satellite galaxies encodes information about the mass accretion history of a dark matter halo and serves as a useful observational probe for the mass distribution in a halo. In this work, we perform the first weak lensing test of the connections between the magnitude gap and the halo profile. We measure the halo profiles of isolated central galaxies (ICGs) selected primarily from the Sloan Digital Sky Survey Main Galaxy Sample. Halo mass and concentration are inferred by fitting stacked lensing profiles in bins of central luminosity, L_c, and the central-satellite magnitude gap, L_gap. We detect dependence on the magnitude gap in both halo properties. The dependence is the strongest in the ICG luminosity range of 10^10.3 < L_c[h^–2L_⊙] ≤ 10^10.7, where halos with smaller gaps have higher masses and lower concentrations. When 10^10.7 < L_c[h^–2L_⊙] ≤ 10^11.1, however, no significant gap dependence is detected. In the range of 10^9.9 < L_c[h^–2L_⊙] ≤ 10^10.3, a disordering of the gap dependence is marginally observable. We compare the observational results with predictions by two light-cone catalogs built from the Illustris TNG300 and the Millennium simulations. The gap dependence in the two mock samples show overall consistency with observations, but neither matches them in all L_c bins to a quantitative level, and the flip in the gap dependence in the lowest luminosity bin is not reproduced in the mocks. We also compare the significance of the gap dependence on halo mass and concentration and find that our measurement prefers the halo-mass dependence over the concentration.