Fig. 1
N2D+ column density versus N2H+ column density. Blue symbols correspond to HMSCs (triangles: “warm” cores, see text); green squares show HMPOs (open squares are upper limits); black asterisks correspond to UC HII regions. The two lines indicate the average values of Dfrac for the HMSC group (i.e. 0.26) and that of both the HMPO and UC HII groups (i.e. 0.04).
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