Point-source test, showing m_n − m_core vs. m_n (left) and m_n vs. R_h (right) for observed sources satisfying our colour restrictions in the M 87 SUB1 field (top) and for modeled point-like emission objects (bottom). The dark lines in the left panels delimit the region within which 96% of the modeled point-like emission objects fall. Observed sources in the top panels are considered as point-like objects if they lie in this region and have a half light radius in the range 1 ≤ R_h ≤ 4 pixels. This range of R_h was chosen such that 95% of the modeled population was included. Red dots represent objects that satisfy both criteria and are thus selected as point-like objects. These criteria are also applied to sources in M 87 SUB2 field.