Etude de l'évolution des poussières interstellaires dans les régions dominées par le rayonnement

Abstract : My PhD thesis is about the study of the interstellar dust evolution in photon-dominated regions. I used data from IRS (Infrared Spectrograph) on board the Spitzer space telescope. This data is part of the SPECPDR program whose aim is to study very small particles and chemistry in photodissociation regions (PDRs). I participated in the reduction and photometric calibration of this data. I also developed modelling tools in order to interpret this data. In particular, I have updated the Désert et al. (1990) dust emission model and developed a radiation transfer model. I demonstrated the presence of aromatic infrared bands (AIBs) emitters in the ionised gas in front of the Horsehead nebula. Their survival in this HII region could be related to the moderate intensity and hardness of the radiation field. The shape of the AIBs spectrum can be explained by the significant presence of neutral emitters. Furthermore, I modelled the Horsehead and the NGGC2023 north PDRs using plan-parallel and spherical geometry, respectively. This modelling allowed me to demonstrate that the relative abundance PAH (Polycyclic Aromatic Hydrocarbons, AIBs emitters)/VSG (Very Small Grains, continuum emitters) appears about 2 times lower in the Horsehead nebula than in Cirrus clouds. This PAH/VSG ratio is equal to the Cirrus value in the outer and diffuse part of NGC2023 and becomes 5 times lower in the inner and denser part of this PDR. I also conclude that very small particles seem to evolve mainly in PDRs and do not evolve much under the effect of the radiation field in the diffuse medium. I proposed some physical processes which could explain these variations in PDRs.
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Submitted on : Wednesday, July 4, 2007 - 1:42:15 PM
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Mathieu Compiègne. Etude de l'évolution des poussières interstellaires dans les régions dominées par le rayonnement. Astrophysique [astro-ph]. Université Paris Sud - Paris XI, 2007. Français. ⟨tel-00159882⟩

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