Comparing simulations of ionisation triggered star formation and observations in RCW 120

TL;DR

This study uses 3D simulations and observations to explore star formation in RCW 120, showing that clump formation can result from initial cloud structure and a hybrid triggering mechanism, not solely the Collect and Collapse process.

Contribution

The paper demonstrates that the observed shell-like clump distribution in RCW 120 can be explained by initial cloud structure and hybrid triggering, challenging the exclusive role of the C&C mechanism.

Findings

Clump distribution can be explained by initial cloud structure.

Shell-like clumps do not necessarily indicate C&C mechanism.

Mass estimates from 870 micron emission are accurate within a factor of two for >100 M_sun clumps.

Abstract

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.