Very small particles in spiral galaxies

Abstract

The existence of a hot component of very small dust particles in normal spiral galaxies has been inferred from a statistical study of their infrared emission as measured by IRAS. Our galaxy has been demonstrated to be a typical spiral and is used to investigate various emission sources for mid-infrared radiation. Young and evolved discrete objects are shown to be of minor importance. Rather, evidence is presented for the diffuse nature of the mid-infrared radiation of galaxies. A fairly quantitative treatment of the emission process leads to the observed quantities.