2008A&A...478..717P

One of the ways to determine the contribution of the dark halo to the gravitational potential of a galaxy is study non-circular (streaming) motions and the associated gas shocks in the bar region. These motions, determined by the potential in the inner parts, can break the disk-halo degeneracy. Here, two main fluid dynamical approaches have been chosen to model the non-circular motions in the bar region; a 2D Eulerian grid code for an isothermal gas (FS2) and a 3D smoothed particle hydrodynamic code (N-body/SPH) The aim of this paper is to compare and quantify the differences in the gas flows of rotating barred potentials obtained using two different fluid dynamical approaches. We analysed the effect of using 2D and a 3D codes in calculating the gas flow in barred galaxies and to what extent the results are affected by the code. To do this, we derived the velocity field and density maps for the mass model of NGC 4123 using a 3D N-body/SPH code and compare the results to the previous 2D Eulerian grid code results. Numerical modelling, 3D N-body/SPH simulations The global velocity field and the gas distribution are very similar in both models. The study shows that the position and strength of the shocks developed in the SPH simulations do not vary significantly compared to the results derived from the 2D FS2 code. The largest velocity difference across the shock is 20 km/s between the 2D and 3D fluid dynamical models. The results when deriving the dark matter content of barred galaxies using the bar-streaming motions and strength and position of shocks are robust to the fluid dynamical model used. The effect of 2D and 3D modelling can be neglected in this type of study.