M 16 Herschel column density map (Hill et al. 2012b). The circles indicate the different regions used for the PDFs. The white crosses indicate the position of the main ionizing sources. The limit of the Hα emission is inside region 1 + 2 + 3 showing approximately the limit of the H ii region (although the H ii region is not spherical in M 16). The blue circles indicate the position of the dense condensations identified in the power-law tail of the PDF of region 1.