Spatial distribution of NIR counterpart of X-ray sources as a function of age. This is compared to a ¹³CO map¹⁰ shown by the grey image superimposed on A_V> 2 and 4 mag contours (the same as Fig. 1). The diamonds, squares, and circles represent objects with less than 5 Myr, between 5 and 10 Myr, and more than 10 Myr, respectively. The counterparts found outside of Siess et al. (2000) PMS isochrones are represented by crosses and disk-bearing candidates (see Sect. 4.1) are shown by blue ellipses. Black circles delimit the fields E, C, S, and W.