Comoving groups identified in the Arches field (blue box in Fig. 1). Left column: PMs. Right column: positions. Top left: Relative PMs, after subtracting the mean residuals with respect to Gaia. Bottom left: absolute PMs. Green points represent the stars identified by the clustering algorithm as members of a comoving group, red crosses mark stars within 1.5 times the radius of the comoving group, and black points correspond to field stars. The boxes indicate the mean PM values with their dispersions, the approximate radius of the comoving group, the number of identified members, and their mean positions.