Synthetic Observations of Line Emission from Simulated HII Regions

Abstract

In this work I post-process a series of simulations of Giant Molecular Clouds (GMC) from Dale (2017), Dale et al. (2014) by running them through MOCASSIN (MOnte CArlo SimulationS of Ionized Nebulae) and studying the emission from the simulated clouds. I present spectral energy distributions (SEDs) from each simulation, including from multiple directions for some runs to highlight how this has no effect on the obtained SED. With these I present a new correlation between how IR/UV ratios evolve with time, and how they change with different initial conditions. I also study the turbulent nature and behaviours of the clouds, determining what could dominate the measured turbulence through observational techniques on these simulations. Because these simulations omit stars lower than 20 Mʘ, I identify the approximate missing luminosity, including from lower mass accretion and show that in spite of the missing stars, the SED results and time-dependent SED relationships are not impacted by this and still remain accurate for our clouds due to the missing emission being negligible with respect the massive stars and reprocessing through the GMC. Dust plays an integral role in the measured emission from molecular clouds, however is a challenging property to accurately model. Given that a dust grain size model is used in this work, I also conduct an experiment using several grain size distributions which highlighted our adopted distribution leads to predictions that, with the exception of distributions found only in circumstellar discs, were in agreement with observation. Finally, I study emission line ratios across the clouds and produce Baldwin, Phillips and Telervin (BPT) maps with known classification lines, and empirically derive new classification lines specific to ionised regions and molecular clouds based upon my results.