Prof. Dimitra Rigopoulou

Abstract:

We report first results on Infrared Space Observatory (ISO) spectroscopic observations of Starburst and Ultraluminous Galaxies. Observations of a wide range of ionic, atomic, and molecular infrared lines enable us to explore in detail the physical conditions in the circumnuclear regions of these galaxies, and to determine, as a first step, parameters such as gas densities and temperatures of ionizing stars. With the help of theoretical modeling this multi-line spectroscopic database is used to further probe the central emission mechanism, discriminate between stellar and non-thermal processes and finally constrain the current models of galactic nuclei.

Abstract:

Spectroscopy with SWS and ISOPHOT-S has opened a new window for studies of the nuclei of external galaxies. We present selected results of observations of starburst galaxies and active galactic nuclei and discuss the mid-infrared extinction law. The flux ratio of high and low excitation fine structure lines and the strength of the 'PAH' emission features are mid-infrared spectroscopic tools that allow to distinguish between starburst and AGNs in heavily obscured galactic nuclei. We have verified these tools on template starburst and AGN galaxies and apply them to a sample of ultraluminous infrared galaxies, finding that most of them are predominantly powered by starburst activity.