Interstellar medium of external galaxies

Disentangling the contribution of each of the phases of the interstellar medium to the energy budget of the medium is almost out-of-reach in our Galaxy because of the complex interfaces and unknown geometry of the structure of each phase. This separation is made possible in external galaxies for which global measurements can be achieved.

Such a project is conducted in the laboratory by M. Gerin and collaborators in Caltech, Paris Observatory and Institut d'Astrophysique Spatiale in Orsay. These observations have revealed the important role played by neutral carbon in the radiative cooling of the gas.