Pillars and globules at the edges of H ii regions, Confronting Herschel
  observations and numerical simulations
  Pillars and globules are present in many high-mass star-forming regions, such
as the Eagle nebula (M16) and the Rosette molecular cloud, and understanding
their origin will help characterize triggered star formation. The formation
mechanisms of these structures are still being debated. Recent numerical
simulations have shown how pillars can arise from the collapse of the shell in
on itself and how globules can be formed from the interplay of the turbulent
molecular cloud and the ionization from massive stars. The goal here is to test
this scenario through recent observations of two massive star-forming regions,
M16 and Rosette. The column density structure of the interface between
molecular clouds and H ii regions was characterized using column density maps
obtained from far-infrared imaging of the Herschel HOBYS key programme. Then,
the DisPerSe algorithm was used on these maps to detect the compressed layers
around the ionized gas and pillars in different evolutionary states. Finally,
their velocity structure was investigated using CO data, and all observational
signatures were tested against some distinct diagnostics established from
simulations. The column density profiles have revealed the importance of
compression at the edge of the ionized gas. The velocity properties of the
structures, i.e. pillars and globules, are very close to what we predict from
the numerical simulations. We have identified a good candidate of a nascent
pillar in the Rosette molecular cloud that presents the velocity pattern of the
shell collapsing on itself, induced by a high local curvature. Globules have a
bulk velocity dispersion that indicates the importance of the initial
turbulence in their formation, as proposed from numerical simulations.
Altogether, this study re-enforces the picture of pillar formation by shell
collapse and globule formation by the ionization of highly turbulent clouds.
