Star formation towards the Galactic HII region RCW120
  The expansion of HII regions can trigger the formation of stars. An
overdensity of young stellar objects (YSOs) is observed at the edges of HII
regions but the mechanisms that give rise to this phenomenon are not clearly
identified. Moreover, it is difficult to establish a causal link between
HII-region expansion and the star formation observed at the edges of these
regions. A clear age gradient observed in the spatial distribution of young
sources in the surrounding might be a strong argument in favor of triggering.
We have observed the Galactic HII region RCW120 with herschel PACS and SPIRE
photometers at 70, 100, 160, 250, 350 and 500$\mu$m. We produced temperature
and H$_2$ column density maps and use the getsources algorithm to detect
compact sources and measure their fluxes at herschel wavelengths. We have
complemented these fluxes with existing infrared data. Fitting their spectral
energy distributions (SEDs) with a modified blackbody model, we derived their
envelope dust temperature and envelope mass. We computed their bolometric
luminosities and discuss their evolutionary stages. The herschel data, with
their unique sampling of the far infrared domain, have allowed us to
characterize the properties of compact sources observed towards RCW120 for the
first time. We have also been able to determine the envelope temperature,
envelope mass and evolutionary stage of these sources. Using these properties
we have shown that the density of the condensations that host star formation is
a key parameter of the star-formation history, irrespective of their projected
distance to the ionizing stars.
