  To characterize the initial conditions for intermediate- to high-mass star
formation, we observed two Infrared Dark Clouds (IRDCs) that remain absorption
features up to 70mum wavelength, with the PdBI in the 3.23mm dust continuum as
well as the N2H+(1--0) and 13CS(2-1) line emission. While IRDC19175-4 is
clearly detected in the 3.23mm continuum, the second source in the field,
IRDC19175-5, is only barely observable above the 3sigma continuum detection
threshold. However, the N2H+(1-0) observations reveal 17 separate sub-sources
in the vicinity of the two IRDCs. Most of them exhibit low levels of turbulence
(dv \leq 1km/s), indicating that the fragmentation process in these cores may
be dominated by the interplay of thermal pressure and gravity, but not so much
by turbulence. Combining the small line widths with the non-detection up to
70mum and the absence of other signs of star formation activity, most of these
17 cores with masses between sub-solar to ~10M_sun are likely still in a
starless phase. Furthermore, we find a large CS depletion factor of the order
100. Although the strongest line and continuum peak is close to virial
equilibrium, its slightly broader line width compared to the other cores is
consistent with it being in a contraction phase potentially at the verge of
star formation. The relative peak velocities between neighboring cores are
usually below 1km/s, and we do not identify streaming motions along the
filamentary structures. Average densities are between 10^5 and 10^6cm^{-3} (one
to two orders of magnitude larger than for example in the Pipe nebula) implying
relatively small Jeans-lengths that are consistent with the observed core
separations of the order 5000AU. The quest for high-mass starless cores prior
to any star formation activity remains open.
