Statistical Multi-Component Fitting in the Orion A Molecular Cloud

Star formation is a process integral to the structure and chemical composition of our universe. While low-mass star formation is fairly well understood, the details of high-mass star formation remain an open problem. The Integral Shaped Filament (ISF) of the Orion A Molecular Cloud is the closest high-mass star forming region to the Solar System, and therefore provides an excellent opportunity to study the environments in which massive stars form. We use NestFit, a Bayesian software framework for spectral line decomposition, to fit up to two gas velocity components to observed ammonia inversion spectra from the Green Bank Ammonia Survey. We compare the results of our two-component model to the single-component fits of Friesen et al. (2017) to determine whether assuming a single velocity component biases model parameter estimates. We find that the resulting distributions for many gas properties do not differ significantly between the one- and two-component models. The two-component model does, however, show a peak in velocity dispersion near the thermal sound speed not found in the one-component results. This indicates the presence of non-turbulent, thermal gas. Maps of the velocity dispersion show that regions of transonic gas correspond to denser regions of Orion A that are more likely to be star-forming. The excess of gas near the sonic speed in areas of dense gas over previous analyses suggests a greater quantity of gas unstable to gravitational collapse in Orion A.