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Testing diagnostics of triggered star formation




We produce synthetic images and SEDs from radiation hydrodynamical simulations of radiatively driven implosion. The imaged bright rimmed clouds (BRCs) are morphologically similar to those actually observed in star-forming regions. Using nebular diagnostic optical collisional line ratios, simulated Very Large Array (VLA) radio images, Hα imaging and SED fitting we compute the neutral cloud and ionized boundary layer (IBL) gas densities and temperatures and perform a virial stability analysis for each cloud. We determine that the neutral cloud temperatures derived by SED fitting are hotter than the dominant neutral cloud temperature by 1–2 K due to emission from warm dust. This translates into a change in the calculated cloud mass by 8–35 per cent. Using a constant mass conversion factor (Cν) for BRCs of different class is found to give rise to errors in the cloud mass of up to a factor of 3.6. The IBL electron temperature calculated using diagnostic line ratios is more accurate than assuming the canonical value adopted for radio diagnostics of 104 K. Both radio diagnostics and diagnostic line ratios are found to underestimate the electron density in the IBL. Each system is qualitatively correctly found to be in a state in which the pressure in the IBL is greater than the supporting cloud pressure, implying that the objects are being compressed. We find that observationally derived mass-loss estimates agree with those on the simulation grid and introduce the concept of using the mass-loss flux to give an indication of the relative strength of photoevaporative flow between clouds. The effect of beam size on these diagnostics in radio observations is found to be a mixing of the bright rim and ambient cloud and H ii region fluxes, which leads to an underestimate of the cloud properties relative to a control diagnostic.

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