Hot Gas Flows on Global and Nuclear Galactic Scales

Since its discovery as an X-ray source with the EinsteinObservatory, the hot X-ray emitting interstellar medium of early-type galaxies has been studied intensively, taking advantage of observations of improving quality performed by the subsequent X-ray satellites ROSAT, ASCA, Chandraand XMM - Newton, and comparing the observational results with extensive modeling by means of numerical simulations. The hot medium originates from the ejecta produced by the normal stellar evolution, and during the galaxy lifetime it can be accumulated or expelled from the galaxy potential well. The main features of the hot gas evolution are outlined here, focussing on the mass and energy input rates, the relationship between the hot gas flow and the main properties characterizing its host galaxy, the flow behavior on the nuclear and global galactic scales, and the sensitivity of the flow to major galaxy properties as the shape of the mass distribution and the mean rotation velocity of the stars.