Prof. Dimitra Rigopoulou

Abstract:

Soon after the IRAS mission, the first ever mission in exploring the Infrared world from space, it was realised that there exists a great number of galaxy populations that are extremely luminous at infrared wavelengths. Yet, their optical output was significantly smaller when compared to their infrared one. The enormous amounts of dust present in these galaxies is of course the reason for the different appearence of these galaxies at different wavelengths. And although optical spectroscopy is generally a useful tool, it can not provide much inside on these galactic nuclei as their centers suffer high extinctions. However, infrared spectroscopy although difficult to be performed from the ground, is the ideal tool for probing the obscured nuclei of galaxies. The Infrared Space Observatory (ISO) provides the best opportunity to probe these obscured nuclei, and even more, promises to open up our view of the infrared world.

Abstract:

The Infrared Space Observatory is opening the 2.5 to 200 mu m band for detailed studies of galaxies. Based an the first results on ionic emission lines obtained with the Short-Wavelength-Spectrometer me discuss the nature of ultra-luminous IR, galaxies.

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.