Structure of the Interstellar Medium around Cas A

Abstract

We present a 3 yr series of observations at 24 μm with the SpitzerSpace Telescope of the interstellar material in a200'×200' square area centered on CassiopeiaA. Interstellar dust heated by the outward light pulse from thesupernova explosion emits in the form of compact, moving features. Theirsequential outward movements allow us to study the complicatedthree-dimensional structure of the interstellar medium (ISM) behind andnear Cassiopeia A. The ISM consists of sheets and filaments, with manystructures on a scale of a parsec or less. The spatial power spectrum ofthe ISM appears to be similar to that of fractals with a spectral indexof 3.5. The filling factor for the small structures above the spatialwavenumber k~0.5 cycles pc-1 is only ~0.4%.