APEX CO observations towards the photodissociation region of RCW120
  The edges of ionized (HII) regions are important sites for the formation of
(high-mass) stars. Indeed, at least 30% of the galactic high mass star
formation is observed there. The radiative and compressive impact of the HII
region could induce the star formation at the border following different
mechanisms such as the Collect & Collapse (C&C) or the Radiation Driven
Implosion (RDI) models and change their properties. We study the properties of
two zones located in the Photo Dissociation Region (PDR) of the Galactic HII
region RCW120 and discussed them as a function of the physical conditions and
young star contents found in both clumps. Using the APEX telescope, we mapped
two regions of size 1.5'$\times$1.5' toward the most massive clump of RCW120
hosting young massive sources and toward a clump showing a protrusion inside
the HII region and hosting more evolved low-mass sources. The
$^{12}$CO($J=3-2$), $^{13}$CO($J=3-2$) and C$^{18}$O($J=3-2$) lines are used to
derive the properties and dynamics of these clumps. We discuss their relation
with the hosted star-formation. The increase of velocity dispersion and
$T_{ex}$ are found toward the center of the maps, where star-formation is
observed with Herschel. Furthermore, both regions show supersonic Mach number.
No strong evidences have been found concerning the impact of far ultraviolet
(FUV) radiation on C$^{18}$O photodissociation. The fragmentation time needed
for the C&C to be at work is equivalent to the dynamical age of RCW120 and the
properties of region B are in agreement with bright-rimmed clouds. It
strengthens the fact that, together with evidences of compression, C&C might be
at work at the edges of RCW120. Additionally, the clump located at the eastern
part of the PDR is a good candidate of pre-existing clump where star-formation
may be induced by the RDI mechanism.
