SPH simulations of clumps formation by dissipative collision of molecular clouds

Abstract

We performed computer simulations of interstellar cloud-cloud collisions using the three-dimensional smoothed particle magnetohydrodynamics method. In order to study the role of the magnetic eld on the pro- cess of collision-triggered fragmentation, we focused our attention on head-on supersonic collisions between two identical spherical molecular-clouds. Two extreme congurations of the magnetic eld were adopted: parallel and perpendicular to the initial clouds motion. The initial magnetic eld strength was approximately 12.0 G. In the parallel case, much more of the collision debris were retained in the shocking region than in the non-magnetic case where gas escaped freely throughout the symmetry plane. Dierently from the non-magnetic case, eddy-like vortices were formed. The regions of highest vorticity and the the regions of highest density are oset. We found clumps formation only in the parallel case, however, they were larger, hotter and less dense than in the analogous non-magnetic case. In the perpendicular case, the compressed eld works as a magnetic wall, preventing a stronger compression of the colliding clouds. This last eect inhibits direct contact of the two clouds. In both cases, we found that the eld lines show a chaotic aspect in large scales. Also, the eld magnitude is considerably amplied in the shock layer. However, the eld distribution is almost coherent in the higher density regions.