A. P. Jones^1,2, L. Fanciullo^1,2, M. Köhler^1,2, L. Verstraete^1,2, V. Guillet^1,2, M. Bocchio^1,2 and N. Ysard^1,2

¹CNRS, Institut d’Astrophysique Spatiale, UMR 8617, 91405 Orsay, France
²Université Paris Sud, Institut d’Astrophysique Spatiale, UMR 8617, 91405 Orsay, France

Context. The evolution of amorphous hydrocarbon materials, a-C(:H), principally resulting from ultraviolet (UV) photon absorption-induced processing, are likely at the heart of the variations in the observed properties of dust in the interstellar medium.
Aims. The consequences of the size-dependent and compositional variations in a-C(:H), from aliphatic-rich a-C:H to aromatic-rich a-C, are studied within the context of the interstellar dust extinction and emission.
Methods. Newly-derived optical property data for a-C(:H) materials, combined with that for an amorphous forsterite-type silicate with iron nano-particle inclusions, a-Sil_Fe, are used to explore dust evolution in the interstellar medium.
Results. We present a new dust model that consists of a power-law distribution of small a-C grains and log-normal distributions of large a-Sil_Fe and a-C(:H) grains. The model, which is firmly anchored by laboratory-data, is shown to quite naturally explain the variations in the infrared (IR) to far-ultraviolet (FUV) extinction, the 217 nm UV bump, the IR absorption and emission bands and the IR-mm dust emission.
Conclusions. The major strengths of the new model are its inherent simplicity and built-in capacity to follow dust evolution in interstellar media. We show that mantle accretion in molecular clouds and UV photo-processing in photo-dominated regions are likely the major drivers of dust evolution.

Reference
Jones AP, Fanciullo L, Köhler M, Verstraete L, Guillet V, Bocchio M and Ysard N (in press) The evolution of amorphous hydrocarbons in the ISM: dust modelling from a new vantage point. Astronomy & Astrophysics
[doi:10.1051/0004-6361/201321686]
Reproduced with permission © ESO

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