Date: Tue 17-Oct-2006
Speaker: Frederic Galliano (NRC NASA GSFC)
Title: Dust Evolution and Spectral Energy Distributions of Galaxies
The evolution of a galaxy shapes its Spectral Energy Distribution (SED). A self-consistent modelling of a galaxy's SED should ideally relate its star formation history and stellar evolution to the subsequent enrichment of its ISM in heavy elements, and to the properties and evolution of the dust grains formed from these elements. It should also take into account the way these grains are distributed into the different phases of the ISM. Understanding the relation between these various processes is probably one of the major challenges of the coming decade. Ultimately, a detailed understanding of the impact of a galaxy's evolution, on its SED, would allow us to address outstanding issues, both in the science of nearby galaxies (by providing powerful diagnostic tools) and in cosmology (by providing physically parametrized SED templates). The rich database of infrared observations of nearby galaxies, obtained by Spitzer and previously by ISO, provides unprecedented constraints on these various physical processes. I will first show that the Polycylic Aromatic Hydrocarbons (PAH) are good indicators of the physical conditions inside galaxies, by studying select band ratios over a large sample of objects, and that PAH properties are remarkably universal. Then, I will illustrate the link between dust evolution and spectral energy distributions, by showing that the evolution of the PAH-to-dust mass ratio, with the metallicity, is a consequence of the delayed injection of PAHs by AGB stars, into the ISM of galaxies. In addition, I will discuss the consequences of the recent discovery of dusty distant quasars, on our understanding of dust production. Finally, I will discuss the prospectives of dust SED modelling, with the future telescopes.
