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Appendix A

A.1. Description of the linewidth distribution

IRDC 18223: we found a clear increase of the linewidth toward the center of IRDC 18223-2, but IRDC 18223-2 and -3 show an increase toward the edge. IRDC 18310: in IRDC 18310-1 the linewidth increases not toward the submm peak, but toward the detected PACS point sources within. IRDC 18310-4 is a 70 μm dark region and the linewidth increases toward its edge. In between IRDC 18310-2, -3, and -4 the measured increase in linewidth is due to two independent, overlapping components. G11.11: while for the two main peaks of G11.11, G11.11-1, and G11.11-2, the linewidth increases prototypically toward its edges, the other clumps of the northern part shown in Fig. 2 show no such clear variation of the linewidth. The systematic offset in the mapping of the southern part of G11.11 does not allow a systematic study of the line parameters. Nevertheless, it is worth noting that the linewidth of the southern part is significantly broader than it is for the northern mapped part. G15.05: no clumps detected at given column density threshold. IRDC 18102: we found an increase in linewidth toward the submm peak with its connected PACS point source. An additional broadening of the linewidth from east to south is prominent as well. IRDC 18151: in IRDC 18151, IRDC 18151-2 has the widest linewidth with 3.1 km s^-1. However, it is known to have an outflow (Beuther & Sridharan 2007), which migh explain the broad linewidth. Both brighter at PACS 70 μm (the associated PACS point source is with 4026  L_⊙~ 10 times more luminous than the one connected to IRDC 18151-2) and with a collimated outflow (Fallscheer et al. 2011) as well, IRDC 18151-1 has a linewidth of only 1.9 km s^-1. Along the dust continuum emission away from the center the linewidth increases again. However, the reported outflow is perpendicular to the dust continuum emission and therefore cannot explain the broadening of the linewidth. Despite its still luminous PACS point source of 184  L_⊙, IRDC 18151-3 has the narrowest linewidth in this region with 0.7 km s^-1. That is consistent with the fact that López-Sepulcre et al. (2011) found no outflows toward that source. IRDC 18182: the well-studied HMPO in the north with four outflows connected to it (Beuther et al. 2006) has a broadening linewidth toward its center. The region of interest, the

IRDC in the southeast has its narrowest linewidth at the peak of IRDC 18182-2. Although there is a PACS continuum source at its peak, Beuther & Sridharan (2007) detected no SiO toward that peak. The southern part of the IRDC, IRDC 18182-4 has a slightly broader linewidth.

IRDC 18308: while the IR dark filament, connected to IRDC 18308-5 and IRDC 18308-6, has a similar linewidth all along between 1 km s^-1 and 2 km s^-1, the southern complex of IRDC 18308 has linewidths broader than 2.5 km s^-1. However, the peak of the linewidth is offset from the submm peaks, but is north of IRDC 18308-1. It is interesting to note that the N₂H⁺ column density is not aligned with the submm continuum peak IRDC 18308-1, and that the N₂H⁺ linewidth peak is offset from the N₂H⁺ column density peak. While the offset between the continuum and the N₂H⁺ emission peak of ~15′′ might be explained by the pointing uncertainties, the offset between the column density peak and the linewidth peak of ~42′′ are not. Since the linewidth and N₂H⁺ column density are measured from the same data, positional uncertainties are not an explanation for their difference of 30′′. As described in 3.3, we checked for the peak of the linewidth map whether its spectrum is fit better by two independent N₂H⁺ velocity components, but only founnd a single component. Because of the high-velocity resolution of 0.1 km s^-1 for that check we can exclude an additional component as the cause of this broadening. G19.30: the linewidth distribution in G19.30 peaks toward the two more massive submm peaks G19.30-1 and -2 with an additional increase in linewidth north of G19.30-1. In between P1 and P2, the linewidth is narrowest within G19.30-3, but still broad with ~2 km s^-1. G28.34: the linewidth in G28.34 is in general very broad with Δv> 2 km s^-1 with only few exceptions. It peaks toward the two main peaks G28.34-1 and -2 with linewidths of up to 3.5 km s^-1. The narrowest linewidth is found to be in between the two main peaks at G28.34-10 at a linewidth of 2.1 km s^-1. Using the maps smoothed to a velocity resolution of 0.4 km s^-1, we found even narrower linewidths along the IR-dark filament beyond G28.34-9. G48.66: the linewidths in G48 are narrower than those of other regions mapped within this sample. For the part where N₂H⁺ is detected, the region with the highest absorption and the embedded but detected PACS sources, the velocity dispersion is broadest and decreases along the filament to lower column densities.

A.2. Parameter maps of omitted regions

A.2.1. Nobeyama 45 m data

Fig. A.1 Parameter map of the omitted region G13.90 mapped with the Nobeyama 45 m telescope. The left panel shows 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 panel displays 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 contours from ATLASGAL 870 μm are plotted with the lowest level representing 0.31 Jy, and continue in steps of 0.3 Jy.

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Fig. A.2 Parameter maps of the region IRDC 18306, mapped with the MOPRA telescope. The left panel shows 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 panel displays 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. The velocity resolution is smoothed to 0.4 km s-1 to improve the signal-to-noise ratio and increase the number of detected N2H+ positions.

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	Fig. A.3 Same as Fig. A.2, but for the region IRDC 18337.
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© ESO, 2014