Comparing simulations of ionisation triggered star formation and   observations in RCW 120
  Massive clumps within the swept-up shells of bubbles, like that surrounding the galactic HII region RCW 120, have been interpreted in terms of the Collect and Collapse (C&C) mechanism for triggered star formation. The cold, dusty clumps surrounding RCW 120 are arranged in an almost spherical shell and harbour many young stellar objects. By performing high-resolution, three-dimensional SPH simulations of HII regions expanding into fractal molecular clouds, we investigate whether the formation of massive clumps in dense, swept-up shells necessarily requires the C&C mechanism. In a second step, we use RADMC-3D to compute the synthetic dust continuum emission from our simulations, in order to compare them with observations of RCW 120 made with APEX-LABOCA at 870 micron. We show that a distribution of clumps similar to the one seen in RCW 120 can readily be explained by a non-uniform initial molecular cloud structure. Hence, a shell-like configuration of massive clumps does not imply that the C&C mechanism is at work. Rather, we find a hybrid form of triggering, which combines elements of C&C and Radiatively Driven Implosion (RDI). In addition, we investigate the reliability of deriving clump masses from their 870 micron emission. We find that for clumps with more than 100 M_sun the observational estimates are accurate to within a factor of two and that, even at these long wavelengths, it is important to account for the radiative heating from triggered, embedded protostars. 
S. Walch, A. Whitworth, T. Bisbas, D. A. Hubber, R. Wuensch
astro-ph.GA astro-ph.CO astro-ph.EP astro-ph.SR physics.comp-ph