Cosmological constraints in the flat ΛCDM model. Left panel: posterior distribution on σ₈ from the cosmological fit of the whole XXL C1 cluster sample (blue line), when lowering the mass calibration by 20% (black dotted line), when using only clusters below z = 0.4 (green dot-dashed line), for Planck clusters (Planck Collaboration XXIV 2016; pink triple dot-dashed line), and for CMB (Planck Collaboration XIII 2016; orange dashed line), rescaled to match the peak of the XXL C1 distribution. Middle panel: countours of 1σ and 2σ in the σ₈ –Ω_m plane obtained from the C1 clusters as a function of redshift. Right panel: comparison of the XXL, KIDS (lensing), and Planck 2015 constraints in the σ₈ –Ω_m plane (1σ and 2σ contours).