Evolution of CG properties. From left to right: i) Group surface brightness, ${\overline{\mu }}_r$; ii) size, ${\overline{R}}_{\mathrm{p}}$; and iii) total luminosity, L_r. Solid blue lines show the sample medians, and shaded regions encompass the 25th-75th percentiles. At the left panel, we show the threshold value, ${\overline{\mu }}_r=26.33\mathrm{mag}{\mathrm{arcsec}}^{-2}$, with a horizontal dashed red line, and the median threshold time, t_thr, is represented with a blue arrow, indicating that more than 50% of the CGs became compact less than 1 Gyr ago. The other two panels show that surface brightness strongly correlates with size evolution, while luminosity mildly changes (Δ ∼ 0.2 dex).