Structure of the interstellar medium around Cas A

TL;DR

This study uses three years of 24-micron observations from the Spitzer Space Telescope to analyze the three-dimensional structure of the interstellar medium around Cassiopeia A, revealing complex filamentary features and fractal-like spatial distribution.

Contribution

It provides detailed three-dimensional mapping of the ISM around Cas A using moving dust features, highlighting its filamentary and fractal nature.

Findings

ISM consists of sheets and filaments on parsec scales

Spatial power spectrum resembles fractals with index 3.5

Small structures have a filling factor of about 0.4%

Abstract

We present a three-year series of observations at 24 microns with the Spitzer Space Telescope of the interstellar material in a 200 x 200 arcmin square area centered on Cassiopeia A. Interstellar dust heated by the outward light pulse from the supernova explosion emits in the form of compact, moving features. Their sequential outward movements allow us to study the complicated three-dimensional structure of the interstellar medium (ISM) behind and near Cassiopeia A. The ISM consists of sheets and filaments, with many structures on a scale of a parsec or less. The spatial power spectrum of the ISM appears to be similar to that of fractals with a spectral index of 3.5. The filling factor for the small structures above the spatial wavenumber k ~ 0.5 cycles/pc is only ~ 0.4%.