a) Distributions of IRGs in L1 in the space of M_star and Σ₅. ULIRGs, LIRGs, MLIRGs, LLIRGs, and non-SF galaxies are plotted with star, circle, triangle, upside down triangle, and square, respectively. Non-SF galaxies are those with SFR_Hα = 0 and SFR_IR = 0 (M_⊙ yr^-1). Error bars indicate the 1σ-dispersion of the distribution. Gray contour map is the number density of non-SF galaxies, and red dots are ULIRGs. b) f_(U)LIRGs contours in the space of M_star and Σ₅. Dots are IRGs.