SPH simulations of clumps formation by dissipative collisions of molecularclouds - II. Magnetic case

We performed computer simulations of interstellar cloud-cloud collisions us ing the three-dimensional smoothed particle magnetohydrodynamics method. In order to study the role of the magnetic field on the process of collision- triggered fragmentation, we focused our attention on head-on supersonic col lisions between two identical spherical molecular-clouds. Two extreme confi gurations of the magnetic field were adopted: parallel and perpendicular to the initial clouds motion. The initial magnetic field strength was approxi mately 12.0 muG. In the parallel case, much more of the collision debris we re retained in the shocking region than in the non-magnetic case where gas escaped freely throughout the symmetry plane. Differently from the non-magn etic case, eddy-like vortices were formed. The regions of highest vorticity and the the regions of highest density are offset. We found clumps formati on only in the parallel case, however, they were larger, hotter and less de nse than in the analogous non-magnetic case. In the perpendicular case, the compressed field works as a magnetic wall, preventing a stronger compressi on of the colliding clouds. This last effect inhibits direct contact of the two clouds. In both cases, we found that the field lines show a chaotic as pect in large scales. Also, the field magnitude is considerably amplified i n the shock layer. However, the field distribution is almost coherent in th e higher density regions.