Hi density distribution driven by supernova ejecta: a simulation study

Abstract

The non-uniform and turbulent nature of the interstellar medium has long been evident from scattering/scintillation studies in the direction of pulsars and compact extra-galactic sources, and also from HI emission/absorption measurements. A prominent source of energy input driving the ISM evolution is thought to be supernova explosions (SNEs). Many researchers have attempted detailed MHD simulations of a supernova-driven ISM to explore this aspect.Our simulation study, in a highly simplified view of the ISM, monitors only the statistical description of the density distribution. As a first step towards assessing what the essential features of the processes underlying a supernova-driven ISM are, we retain only the kinematical and structural components and assume that these are entirely determined by SNEs alone. We examine the resultant density distributions and associated power-spectral description.In the first of the two approaches explored here, the simulated volume is populated simply with voids of a range of sizes and locations (chosen randomly), such that no new void overlaps with any old one. This may relate to a snap-shot distribution of remnant voids, although somewhat artificially constrained by the non-overlap criterion. In the second approach, a simplified time evolution (considering momentum conservation as the only governing process) is followed as SNE populate the space with the associated input mass & energy. The location & epoch of each SNE and the associated (debris) mass are picked randomly from respective predefined ranges.We describe these simulations and present our results in the form of images of the mass & velocity distribution and the associated power spectra. The latter are compared with trends indicated by available observations. We briefly discuss the limitations of our simulations and the implications of our results. This work was made possible by the NAIC REU and NSF.