Parallel Tree–SPH: A Tool for Galaxy Formation.

We describe a new implementation of a parallel Tree-SPH code with the aim of simulating galaxy formation and evolution. The code has been parallelized using SHMEM, a Cray proprietary library to handle communications between the 256 processors of the Silicon Graphics T3E massively parallel supercomputer hosted by the Cineca Super-computing Center (Bologna, Italy). The code combines the smoothed particle hydrodynamics (SPH) method to solve hydrodynamical equations with the popular Barnes and Hut (1986) tree-code to perform gravity calculation with a N × log N scaling, and it is based on the scalar Tree-SPH code developed by Carraro et al. (1998). Parallelization is achieved by distributing particles along processors according to a workload criterion. Benchmarks of the code, in terms of load balance and scalability, are analysed and critically discussed against the adiabatic collapse of an isothermal gas sphere test using 2 × 10⁴ particles on eight processors. The code turns out to be balanced at more than 95% level. If the number of processors is increased, the load balance worsens slightly. The deviation from perfect scalability at increasing number of processors is negligible up to 64 processors. Additionally we have incorporated radiative cooling, star formation, feedback and an algorithm to follow the chemical enrichment of the interstellar medium. [ABSTRACT FROM AUTHOR]