The contribution of CHONS particles to the diffuse high-Galactic-latitude IR emission

Abstract

This work purports to model the far-infrared grey-body emission in the spectra of high-Galactic-latitude clouds. Several carbonaceous laboratory materials are tested for their fitness as carriers of this modified blackbody emission which, according to data delivered by the Planck satellite, and others before, is best fitted with temperature 17.9 K and spectral index β = 1.78. Some of these materials were discarded for insufficient emissivity, others for inadequate β. By contrast, CHONS clusters (β = 1.4, T = 19 K) combine nicely with magnesium silicate (β = 2, T = 18.7 K) to give a spectrum which falls well within the observational error bars (total emission cross-section at 250 μm: 8.6 × 10^-26 cm² per H atom). Only 15 per cent of all Galactic carbon atoms are needed for this purpose. The CHONS particles that were considered and described have a disordered (amorphous) structure but include a sizeable fraction of aromatic rings, although they are much less graphitized than a-C:H/hydrogenated amorphous carbon. They can be seen as one embodiment of `astronomical graphite' deduced earlier on from the then available astronomical observations.

Grain heating by H atom capture is proposed as a contributor to the observed residual emissions that do not follow the dust/H I correlation.