CO and [CII] line emission of molecular clouds -- the impact of stellar feedback and non-equilibrium chemistry
arXiv:2206.06393
Abstract
We analyse synthetic CO, CO, and [CII] emission maps of simulated molecular clouds of the SILCC-Zoom project, which include an on-the-fly evolution of H, CO, and C. We use simulations of hydrodynamical and magnetohydrodynamical clouds, both with and without stellar feedback. We introduce a novel post-processing of the C abundance using CLOUDY, to account for further ionization states of carbon due to stellar radiation. We report the first self-consistent synthetic emission maps of [CII] in feedback bubbles, largely devoid of emission inside them, as recently found in observations. The C mass is only poorly affected by stellar feedback but the [CII] luminosity increases by per cent compared to runs without feedback. Furthermore, we investigate the capability of the CO/[CII] line ratio as a tracer of the amount of H in the clouds and their evolutionary stage. We obtain, for both CO and CO, no clear trend of the luminosity ratio, . It can therefore \textit{not} be used as a reliable measure of the H mass fraction. We note a monotonic relation between and the H fraction when considering the ratio for individual pixels of our synthetic maps, but with large scatter. Moreover, we show that assuming chemical equilibrium results in an overestimation of H and CO masses of up to 110 and 30 per cent, respectively, and in an underestimation of H and C masses of 65 and 7 per cent, respectively. In consequence, would be overestimated by up to 50 per cent, and be underestimated by up to 35 per cent. Hence, the assumption of chemical equilibrium in molecular cloud simulations introduces intrinsic errors of a factor of up to in chemical abundances, luminosities and luminosity ratios.
18 pages, 18 figures including appendix, modified. Submitted to MNRAS