X-ray halos in galaxies

A hot phase of the interstellar medium has now been detected and studiedin several objects through its X-ray emission. A proper assessment ofits characteristics is relevant for our understanding of several aspectsof galaxy properties, from the large scale distribution of matter to thestellar and galaxian evolution, to the dynamics of systems and tothe feeding of a central black hole. I will briefly summarizeour current understanding of some of the main issues related to the hot gaseouscomponent in galaxies that are fast evolving given the ever morestriking and interesting details provided by theX-ray satellites currently operating. I hope to convince you that the X-ray characteristicsof the hot gas are quite complex, both inmorphology and spectra, in a wide range of objects, which shouldpromote greater efforts in understanding the role playedby this component in all galaxies.