gas lost by stars will expand into the Dark Matter halo and heat up to an energy overwhelming the gravitational potential, it will escape the galaxy. Most likely a sort of dynamical equilibrium is reached in which gas is continuously ejected by stars and lost by the galaxy. It may happen therefore that some amount of gas is always present in the galaxy. The question is not trivial because if an early type galaxy is free of gas and contains only stars, the SED is expected to drop off long-ward of about $2 \mu m$ and no IR emission should be detected. However, as already pointed out long ago by @Guhathakurta86 [@Knapp89] (see also Fig. \[X2\]), many early-type galaxies of the local universe emit in the IR. The origin of this flux in the MIR/FIR is likely due to dust present in a diffuse ISM which, heated up by the galactic radiation field, emits at those wavelengths. Therefore to match the IR emission one has to allow for some amount of diffuse ISM. An interesting question to rise is therefore: how much gas can be present today in an elliptical galaxy and how is it distributed across the galaxy? Even 