Parameter maps of the regions IRDC 18151, IRDC 18182, and IRDC 18308, each mapped with the MOPRA telescope. The left panels of each row are the PACS 70 μm maps with the PACS point sources detected by Ragan et al. (2012a) indicated by red circles, the blue numbers refer to the submm continuum peaks as given in Table 3. The second panels display the N₂H⁺ column density derived from fitting the full N₂H⁺ hyperfine structure. The third and fourth panels show the corresponding velocity and linewidth (FWHM) of each fit. The green contours are from ATLASGAL 870 μm at 0.31 Jy, 0.46 Jy, and 0.61 Jy, continuing in steps of 0.3 Jy. For IRDC 18151 the contours are MAMBO 1.2 mm observations, starting at 60 mJy in steps of 60 mJy. In all three maps the velocity resolution is smoothed to 0.4 km s^-1.