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Fig. 3


Column density of HCO vs. H13CO+ (left) and C2H (right). For W49 only the “spiral arm” feature at 40 km s-1 is shown at left using data from the present work; at right the C2H data of Godard et al. (2010) is used for the 40 km s-1 and 60 km s-1 features. Data from the Horsehead PDR (TdC) are from Gerin et al. (2009). The dashed lines have power-law slope of unity, with proportions of 16:1 and 1:10 at left and right, respectively. Error bars in this and all other plots are 1σ statistical uncertainties.

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