How to isolate galactic bars in simulations

Abstract The presence of bars, which are strongly non-axisymmetric structures, greatly influences the dynamical evolution of galaxies. Although orbit classification methods are the most reliable way to associate stars with bars, they require high temporal resolutions and long integration times. We present here updates to the Galactic Structure Finder code, which allow for robust identification of bars in simulated galaxies using only single snapshot information. As test cases, we used three galaxies from the Illustris TNG50 project, ranging from non-barred to strongly barred. Based on our bar identification, we propose a new method to measure the bar pattern speed from single simulation snapshots, without having to consider the contamination from the stellar disk(s). We also propose a new robust way to measure the dynamical lengths of simulated bars based on the gradient of rotational velocity contrast with respect to the velocity imposed by the gravitational potential. The clean isolation of the bar from the galaxy allows us to precisely quantify the bar properties: mass, strength, pattern speed, stellar age, and metallicity distributions. The ability to accurately estimate bar properties opens up a new window for precisely quantifying the effect of bars on the evolution of galaxies (e.g. bulge formation, transfer of angular momentum to the inner dark matter halo, growth of the central super-massive black hole).