Distribution of M₂₀₀ as a function of redshift for the X-ray detected groups in the COSMOS survey up to z = 1.0. The black filled circles are the COSMOS groups used in this work. Large red open circles mark the systems excluded from the analysis because they are out of the SUBARU area. Small empty circles mark low-significance and low-quality groups excluded from the analysis. Rectangles show the redshift bins in which the sample is divided, while the dashed lines show the threshold we used to define “high-mass” and “low-mass” groups (6 × 10¹³ M_⊙).