Ultraviolet photoproduction of ISM dust

Laboratory characterisation and astrophysical relevance

¹ Institut d'Astrophysique Spatiale, UMR – 8617, Université Paris-Sud, Bâtiment 121, 91405 Orsay Cedex, France e-mail: emmanuel.dartois@ias.u-psud.fr
² Laboratoire des Sciences de la Terre, UMR 5570 CNRS, École Normale Supérieure de Lyon, 46 allée d'Italie, 69364 Lyon Cedex 07, France

Received: 30 September 2004
Accepted: 30 October 2004

Abstract

The production of a hydrogenated amorphous carbon polymer (a-C:H) via the photolysis of a series of organic molecule precursors at low temperature is described. Such amorphous material is synthesised under interstellar conditions (10 K and Lyman-α photons) and represents the best candidate to explain the Diffuse Interstellar Medium absorption observed in our Galaxy and in other galaxies. We perform a series of laboratory analyses (Infrared spectroscopy, μspectroscopy, Raman, Photoluminescence and UV-visible spectroscopy) which allow a full characterisation of such polymers. This allows us to assess the importance of the polymer and possible scenarios for its role in crucial aspects of the lifecycle of dust. Such material has implications for the carbon budget at galactic scales, hydrogen formation, extended red emission, as a PAH precursor, and in explaining the 2175  extinction bump.