After general considerations on the properties of distribution functions (DF) for steady state stellar systems, I will talk about the choice of the DF. In the 3D gravitational context, I deal with a very old Chandrasekhar's conjecture (1942): What are the properties of a stellar system which DF depends only on the mean particle energy E (The

The characteristics of the halo gas and its interaction with the galactic disk in spiral galaxies are poorly known; this is particularly true for the warm neutral gas associated with HVCs and galactic chimneys. The detection of absorption features such as the NaI D or the CaII (H,K) lines is instrumental to study its detailed physical properties

Magnetic fields play an important role in astrophysics and they often dominate the behavior of magnetized media. We simulate the mechanism (Tagger et al., 1995) by which turbulence in a weakly ionized plasma, as it cascades to the ambipolar scale (where the neutrals are imperfectly coupled to the ions) leads to a filamentation of the magnetic flux

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We show the results of a mid and far IR study of ISO data of the CfA Seyfert sample. These data allow a detailed study of the far IR Spectral Energy Distribution (SED) of these galaxies. We find that the mid and far IR SED of Seyfert galaxies can be explained solely through thermal reradiation of high energy photons by dust, and, that this thermal