SPH simulations of clumps formation by dissipative collision of molecular clouds

I. Non magnetic case

¹ Instituto de Geociências e Ciências Exatas, Departamento de Estatística, Matemática Aplicada e Computacional, UNESP, Rua 10, 2527, 13500-230, Rio Claro SP, Brazil
² Instituto Astronômico e Geofıisico, Departamento de Astronomia, USP, Av. Miguel Stefano, 4200, 04301-904 São Paulo SP, Brazil

Send offprint request to: E.P. Marinho

Received: 7 September 1999
Accepted: 17 December 1999

Abstract

Computer experiments of interstellar cloud collisions were performed with a new smoothed-particle-hydrodynamics (SPH) code. The SPH quantities were calculated by using spatially adaptive smoothing lengths and the SPH fluid equations of motion were solved by means of a hierarchical multiple time-scale leapfrog. Such a combination of methods allows the code to deal with a large range of hydrodynamic quantities. A careful treatment of gas cooling by H, H₂, CO and HII, as well as a heating mechanism by cosmic rays and by H₂ production on grains surface, were also included in the code. The gas model reproduces approximately the typical environment of dark molecular clouds. The experiments were performed by impinging two dynamically identical spherical clouds onto each other with a relative velocity of 10 km s^-1 but with a different impact parameter for each case. Each object has an initial density profile obeying an r^-1-law with a cutoff radius of 10 pc and with an initial temperature of 20 K. As a main result, cloud-cloud collision triggers fragmentation but in expense of a large amount of energy dissipated, which occurred in the head-on case only. Off-center collision did not allow remnants to fragment along the considered time ( Myr). However, it dissipated a considerable amount of orbital energy. Structures as small as 0.1 pc, with densities of  cm^-3, were observed in the more energetic collision.