Kinematics in partially ionized molecular clouds: Implications for the transition to coherence

Abstract

A previous paper by Bailey & Basu shows analysis of density and mass-to-flux ratio maps for simulations with either an ionization profile which takes into account photoionization (step-like profile) or a cosmic ray only ionization profile. We extend this study to analyze the effect of these ionization profiles on velocity structures, kinematics, and synthetic spectra. Clump regions are found to occur at the convergence of two flows with a low velocity region and velocity direction transition occurring at the junction. Models with evident substructure show that core formation occurs on the periphery of these velocity valleys. Analysis of synthetic spectra reveals the presence of large non-thermal components within low-density gas, especially for models with the step-like ionization profile. All cores show small, sub-thermal relative motions compared to background gas. Large deviations within this analysis are due to the line of sight intersecting low- and high-density regions across the velocity switch transition. Positive deviations correspond to a foreground core moving away from the observer while negative deviations correspond to a background core moving toward the observer. Comparison of velocities resulting from different ionization profiles suggest that high ionization fractions yield supersonic velocities, up to two times the sound speed, while regions with low ionization fractions tend to be subsonic or mildly supersonic. This suggests that the transition to coherence within cores could be a transition between high and low ionization fractions within the gas.