Heterogeneous interactions in the interstellar medium.

摘要

Heterogeneous processes exist on a variety of astrophysical scale---from galaxies, to star-forming regions, to stars themselves. Such heterogeneous (clumpy) processes are a rich area of investigation. The Hubble Space Telescope (HST) has opened up a window to, for example, the small-scale heterogeneity of jet-like Herbig-Haro (HH) objects. Complementing this, the vast improvements of computing capability over the past several decades have allowed theory-driven direct numerical simulation to thrive. The present work is the result of several sets of simulations---employing adaptive mesh refinement (AMR) with the AstroBEAR code---seeking to address questions related to clumpy astrophysical jets. While their morphology typically is ascribed to a periodic or otherwise smoothly-time-varying launching engine, two alternatives are proposed. The first examines the role of heterogeneity in the jets' environment. Several important correspondences between the simulations and observations are found. Conversely, a model is proposed in which the jets themselves are heterogeneous. Via a study of parameter space based on the degree of "clumpiness," agreement with observations is found, primarily in morphological and kinematic signatures. Finally, the "clumpy jet" model brings to light questions concerning the clumps themselves. Specifically, how the concept of sufficient resolution needs to be modified when the additional physical process of radiative cooling is included. Radiative cooling removes energy from these systems primarily from shock-heated gas. Since many observations derive from the same shock-heating mechanisms, correct modelling when radiative cooling is included is very important. This question is addressed with a suite of simulations which cover several decades in resolution. Finally, a new criterion is proposed to take into account the role of radiative cooling when AMR is employed.