21 μm to 1.2 mm flux ratio versus the normalized angular separation between millimeter and infrared sources. Blue open circles correspond to Type 1 sources (only millimeter emission), green filled circles correspond to Type 2 sources (association between millimeter and infrared emission), and red stars correspond to Type 3 sources (only infrared emission). Blue symbols (millimeter-only sources) are upper limits in which we have considered an upper limit of four times the rms noise in the MSX image. Red symbols (infrared-only sources) are lower limits in which we considered an upper limit of four times the rms noise in the SEST image.