Spatial distribution of the NIR counterparts of the YSOs identified according to four different indicators, as explained in the text, overlaid with the K_s image. Also drawn, a contour of the surface density of K_s sources. Only objects with K_s ≤ 13.5 (unlike Fig. 8, where K_s ≤ 16 has been used) have been selected. a) YSOs identified on the basis of their IRAC colours: red symbols for Class II sources, a large blue triangle marks the only Class I source; b) YSOs identified on the basis of their combined JH(HK_s) [4.5] colours; c)JHK_s sources exhibiting a colour excess; d) X-ray sources. A colour version of this figure is available in the on-line edition.