Probing the initial conditions of high-mass star formation. III.
  Fragmentation and triggered star formation
  Massive clumps tend to fragment into clusters of cores and condensations,
some of which form high-mass stars. In this work, we study the structure of
massive clumps at different scales, analyze the fragmentation process, and
investigate the possibility that star formation is triggered by nearby HII
regions. We present a high angular resolution study of a sample of 8 massive
proto-cluster clumps. Combining infrared data, we use few-arcsecond resolution
radio- and millimeter interferometric data to study their fragmentation and
evolution. Our sample is unique in the sense that all the clumps have
neighboring HII regions. Taking advantage of that, we test triggered star
formation using a novel method where we study the alignment of the centres of
mass traced by dust emission at multiple scales. The eight massive clumps have
masses ranging from 228 to 2279 $M_\odot$. The brightest compact structures
within infrared bright clumps are typically associated with embedded compact
radio continuum sources. The smaller scale structures of $R_{\rm eff}$ $\sim$
0.02 pc observed within each clump are mostly gravitationally bound and massive
enough to form at least a B3-B0 type star. Many condensations have masses
larger than 8 $M_\odot$ at small scale of $R_{\rm eff}$ $\sim$ 0.02 pc.
Although the clumps are mostly infrared quiet, the dynamical movements are
active at clump scale ($\sim$ 1 pc). We studied the spatial distribution of the
gas conditions detected at different scales. For some sources we find hints of
external triggering, whereas for others we find no significant pattern that
indicates triggering is dynamically unimportant. This probably indicates that
the different clumps go through different evolutionary paths. In this respect,
studies with larger samples are highly desired.
