Schwarzschild Modeling of Barred S0 Galaxy NGC4371 with TIMER Survey

Barred structures are important in understanding galaxy evolution, but they were not included explicitly in most dynamical models for nearby galaxies due to their complicated morphological and kinematic properties. The first step for constructing galactic dynamical models is reconstructing the 3D intrinsic density distribution of a galaxy from the 2D image, which is challenging, especially for barred galaxies. We present a method for deprojecting barred galaxies based on multi-Gaussian expansion (MGE), and we validate the approach by testing against mock images created from an N-body simulation with a peanut-shaped bar. Our model can generally recover the 3D density distribution of disc and inner barred bulge regions. Then, we modify the triaxial orbit-superposition Schwarzschild implementation by van den Bosch et al. to include barred structures explicitly. We consider the figure rotation of the galaxy with the bar pattern speed as a free parameter. We first validated the method by applying it to mock IFU data created from an N-body simulation. The model is able to fit the surface density and all kinematic features well. The bar pattern speed is recovered with a relative uncertainty smaller than 10%. The orbital structures in our best-fitting model recover well the true structures in the N-body simulation, particularly the boxy/peanut shaped structure. We then applied the method to the barred galaxy NGC4371 observed with TIMER and SOURAN projects. The gravitational potential combines a spherical dark matter halo, stellar mass, and a fixed black hole mass. We measure the bar pattern speed to be 23 ± 3 km/s/kpc under both the kinematic data of TIMER and SOURAN. We derived the bar rotation rate parameter to be R_co/R_bar > 2.0, indicating a slow bar in NGC4371, which is consistent with its old age and the scenario that bar could slow down over time. We further discuss the improvement of our new approach compared to previous models applied to large sample of spiral galaxies without including the bar explicitly in literature.