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

Abstract

This work purports to model the far infrared gray-body emission in the spectra of high-Galactic-latitude clouds. Several carbonaceous laboratory materials are tested for their fitness as carriers of this modified-black-body emission which, according to data delivered by the Planck satellite, and others before, is best fit with temperature 17.9 K and spectral index beta=1.78. Some of these materials were discarded for insufficient emissivity, others for inadequate beta. By contrast, CHONS clusters (beta=1.4, T=19 K) combine nicely with magnesium silicate (beta=2, T=18.7 K) to give a spectrum which falls well within the observational error bars (total emission cross-section at 250 mum: 8.6 10^{-26} cm^{2} per H atom). Only 15 % 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 sizable fraction of aromatic rings, although they are much less graphitized than a-C:H/HAC. 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/HI correlation.Comment: 11 pages, 13 figures To be published in MNRA