Seminary of Mathieu Bertin

Séminaire de Mathieu Bertin du LERMA de l'observatoire de Paris Laboratory astrophysics studies of VUV and X-ray induced photodesorption of molecules from interstellar ice analogues The recent advances in space and ground based telescopes (ALMA, NOEMA, JWST…) have allowed, and will allow in the coming months, the detection of more and more molecules in the gas phase in the coldest regions of the interstellar medium - ISM (star-forming regions, protoplanetary disks…). The puzzling detection of these gaseous species, including small organic molecules, in media where the temperature is very low (~ 10-100 K), is currently a major and still open question, directly linked to the astrochemical richness. Most of the observed molecules are indeed expected to either directly form or accrete on the surface of dust grains, and cannot thermally desorb in the regions where they are detected. Their observation requires thus non-thermal desorption processes, among which the desorption induced by UV or X-ray photons – so-called photodesorption –  is a promising candidate. Understanding and quantifying this process is thus of primary importance for a proper modelling of observations and chemistry in space. However, much of the underlying mechanisms is still poorly constrained.  
I will present the outcomes of recent laboratory astrophysics studies base on the use of the monochromatic and tunable synchrotron radiation, dedicated to understand and quantify the photodesorption processes in both the vacuum UV (7-13,6 eV) and soft X-rays (500 – 1500 eV) energy ranges. The role played by the photon energy and of the molecular ice composition on the desorption yields will be highlighted. I will finally present the perspective of this work and the framework of the recent ANR PIXyES project, which involves experimental work at the LERMA and at the ISMO institute, and theoretical simulations performed at the PhLAM.