a) Stellar mass ratio between IRGs and their nearest neighbor galaxy, and b) projected distance to the nearest neighbor galaxy of IRGs (R_n / r_vir,nei) as a function of L_IR of IRGs in L1 plus L2. IRGs (M_r ≤  − 21) having late-type neighbors at R_n ≤ r_vir,nei are shown. Large filled circles and vertical error bars represent the median values and their errors in L_IR bins that are represented by horizontal error bars . The dashed horizontal line in a) divides IRGs into major (mass ratio  < 4) and minor (mass ratio  > 4) mergers.