Color–color and color–magnitude diagrams used to identify contaminant objects among the sources with detection at all four IRAC bands following the criteria in Gutermuth et al. (2009). The background logarithmic gray scale indicates the overall source density in each color–color and color–magnitude space. In panels (a) and (b), PAH galaxies are marked with green circles. In panel (c), candidate AGNs are marked by red circles. Panel (d) shows knots of shocked emission (orange circles) and PAH-contaminated sources (blue circles).