Preview

PDF, English Download (34MB) | Terms of use

Abstract

Stars form within molecular clouds in galaxies. Therefore, understanding the formation, evolution and collapse of molecular clouds is critical for understanding galactic evolution. We present a systematic series of numerical simulations of a kiloparsec-scale size, elongated box, with sub-parsec resolution, developed to study the dynamics of molecular clouds in a galactic environment. We explore the origin of empirically observed relations such as the velocity dispersion-size relation in molecular clouds (Chapter 4), where we find that supernova explosions appear to be ineffcient at driving strong turbulent motions inside the clouds, where instead gravity appears to be the dominant process driving the observed fast motions. However, supernova explosions do play an important secondary role in the mass accretion histories of molecular clouds, simultaneously enhancing and suppressing inflow of gas onto the clouds by compressing and disrupting their mass reservoirs, (Chapter 5). We complete our analysis by studying the relative importance of magnetic fields in the evolution of molecular clouds and their envelopes. We find that, although we recover magnetic field strengths comparable to the observed values, they appear unable to prevent clouds from collapsing but capable of maintaining the diffuse envelopes supported, while restricting the gas flows in the diffuse ISM along field lines (Chapter 6). Together these results strongly support a picture of molecular clouds as highly dynamical objects that collapse quickly, and shortly after begin forming stars. However the subsequent evolution of these clouds must be strongly influenced by the newborn stars to avoid star formation effciencies higher than those observed.