Recovering pattern speeds of simulated face-on barred galaxies via Schwarzschild modelling
Stellar bars are a major driving force in the secular evolution of their host galaxies. To better understand the connections between the 3D bar density structure, its orbital composition, stellar populations, and underlying dark matter distribution, it is desirable to construct detailed dynamical models of barred galaxies. However, only a few external barred galaxies have been studied in this way so far. We present a new Schwarzschild orbit superposition code for triaxial potentials with figure rotation and test it extensively using mock data from an N-body simulation of a strongly barred galaxy. We investigate the recovery of model parameters in the nearly face-on case which was not previously considered. In particular, we demonstrate a 10% accuracy of both the pattern speed and mass-to-light ratio and a 20% accuracy for the dark matter halo mass scaling at the inclination 20°. Surprisingly, we obtain a similarly accurate result for the pattern speed in an exact face-on limit, where conventional methods such as Tremaine-Weinberg are no longer applicable. This result suggests that varying the pattern speed at fixed bar length, corresponding to the transition between slow and fast bars, alters the distribution function in a way that produces a systematic change in the vertical velocity distribution, which can not be compensated by the in-plane velocity components.