Cloud angular momentum and effective viscosity in global SPH simulations with feedback

Abstract

We examine simulations of isolated galaxies to analyse the effects of localized feedback on the formation and evolution of molecular clouds. Feedback contributes to turbulence and the destruction of clouds, leading to a population of clouds that is younger, less massive, and with more retrograde rotation. We investigate the evolution of clouds as they interact with each other and the diffuse interstellar medium, and determine that the role of cloud interactions differs strongly with the presence of feedback: in models without feedback, scattering events dramatically increase the retrograde fraction, but in models with feedback, mergers between clouds may slightly increase the prograde fraction. We also produce an estimate of the viscous time-scale due to cloud–cloud collisions, which increases with increasing strength of feedback (t_ν ∼ 20 Gyr versus t_ν ∼ 10 Gyr), but is still much smaller than previous estimates (t_ν ∼ 1000 Gyr); although collisions become more frequent with feedback, less energy is lost in each collision than in the models without feedback.