Map of the density of background stars chance-aligned with K2-19, integrated within an angular separation of up to 4′′, as a function of its magnitude in the z′-band. The negative-slope hatched region displays all the stars that would have been significantly detected in the AstraLux lucky-imaging data with more than 5σ. The negative-slope and vertical hatched regions display the stars that are too faint to reproduce the observed transit depth of K2-19b and c, respectively.