1. WHY IS HOT GAS IMPORTANT?

Because of the implications and relations that a hot phase of the interstellar/intergalactic medium has with several other galaxy-related issues, understanding its properties has become more relevant and intriguing. As just a few examples, gas is closely related to:

• galaxy structure. Gas can be traced at large galactic radii and has been used to study and measure the total gravitational mass in early type galaxies (e.g. Fabricant & Gorenstein 1983)
• evolution of stars, of galaxies and of larger systems. Metal enriched material that is formed in stars gives a measure of stellar evolution; metal gradients indicate how far (how?) metals have traveled from their formation sites; metal concentrations in specific locations could indicate local stripping phenomena
• the dynamics of systems. At high energies different phenomena such as stripping and shocks could be discovered and studied
• active nuclei, who are nourished by gas accretion. When hot, the gas could indeed starve the nucleus rather than feed it, and explain the lack of activity or periodic cycles

The main question is then to find the best candidates to efficiently study the properties of this phase of the InterStellarMedium (ISM).