Scaling relations used for the galaxy selection. Left panel: mean effective surface brightness vs total magnitude (r-band) plane for catalog objects that passed the first selection cut. The black solid line is the linear fit of the redshift confirmed cluster members. The data of Christlein & Zabludoff (2003) are represented by red open circles. The dotted line indicates 2 standard deviations from the cluster sequence: the objects in the shaded gray area are removed from the sample. Right panel: color-magnitude diagram for galaxies that passed the first two cuts. Orange triangles are early-type galaxies found by Misgeld et al. (2008), and the orange solid line is their CMR. The dashed line is the 2 rms level we use to define galaxies as members of the Hydra I cluster.