Kelvin-Helmholtz instability in three dimensional radiative jets

The analysis of the stability properties of astrophysical jets against Kelv in-Helmholtz (or shear-layer) instabilities plays a basic role in the under standing of the origin and physical characteristics of these objects. Numer ical simulations by Bodo et al. (1998) have shown that the three-dimensiona l non-linear evolution of KH instabilities in supersonic jets is substantia lly faster than in the two-dimensional case, leading to a cascade of modes towards smaller scales and a very effective mixing and momentum transfer to the ambient medium. On the other hand, Rossi et al. (1997) and Micono et a l. (1998) found, in two dimensions, that radiative losses tend to reduce an d delay mixing effects and momentum transfer to the ambient medium. In this paper, as a logical next step, we investigate the effects of radiative los ses on the stability of 3D supersonic jets, assuming that the internal jet density is initially lower, equal and higher than the ambient medium, respe ctively. We find that light and equal density radiative jets evolve in a qu alitatively similar fashion with respect to the corresponding adiabatic one s. Conversely, we note substantial differences in the evolution of heavy je ts: they remain more collimated and do not spread out, while the momentum g ained by the ambient medium stays within similar to 5 jet radii.