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Fig. 4

image

Derived column density spectra of OH (gray filled histogram) and OH+ (red lines) toward continuum sources in the first quadrant. Here and in the following figures NV denotes the velocity-specific column density, i.e., the column density within a velocity interval is the area under the histograms. The green hashed area indicates the velocity range spanned by the OH and CH3OH masers in the hot cores where the derived column densities are uncertain due to saturated absorption and excitation of higher levels (for details see Table 2).

This figure is made of several images, please see below:

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