Orbit-superposition Dynamical Modeling of Barred Galaxies

Abstract

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. We modify the triaxial orbit-superposition Schwarzschild implementation by van den Bosch et al. to include barred structures explicitly. The gravitational potential is a combination of a spherical dark matter halo and stellar mass; with the 3D stellar density distribution deprojected from the observed 2D image using a two-component deprojection method, including an axisymmetric disk and a triaxial barred bulge. We consider figure rotation of the galaxy with the bar pattern speed as a free parameter. We validate the method by applying it to a mock galaxy with integral field unit (IFU) data created from an N-body simulation with a boxy/peanut or X-shaped bar. Our model fits the observed 2D surface density and all kinematic features well. The bar pattern speed is recovered well with a relative uncertainty smaller than 10%. Based on the internal stellar orbit distribution of the model, we decompose the galaxy into an X-shaped bar, a boxy bulge, a vertically extended structure and a disk, and demonstrate that our model recovers these structures generally well, similar to the true structures in the N-body simulation. Our method provides a realistic way of modeling the bar structure explicitly for nearby barred galaxies with IFU observations.

The bar rotation rate as a diagnostic of dark matter content in the centre of disc galaxies

“…Several methods have been developed to recover the dynamical structure of a galaxy from broad-band imaging and longslit/integral-field spectroscopy, but the dynamical modelling of barred galaxies is still at an early stage. The recently developed orbit-superposition Schwarzschild models by Vasiliev & Valluri ( 2020 ) and Tahmasebzadeh et al ( 2022 ), which to date have been applied only to data from N -body simulations, considered the bar pattern speed. Portail et al ( 2016 ) built a dynamical model of the Milky Way to reco v er its bar pattern speed by using the made-to-measure method as implemented by de Lorenzi et al ( 2007 ).…”

“…Finally, NGC 4264 and NGC 4277 are amongst the barred galaxies with the best-studied bar properties in terms of surface-brightness distribution, stellar kinematics, and mass modelling. For this reason, they are ideal candidates to be adopted as a test bench in applying the orbit-superposition Schwarzschild dynamical models, which have been recently developed for tumbling bars by Vasiliev & Valluri ( 2020 ) and Tahmasebzadeh et al ( 2022 ) but which have been applied to date only to mock galaxies created from N-body simulations.…”

The Fornax3D project: Environmental effects on the assembly of dynamically cold disks in Fornax cluster galaxies

“…The orbit-superposition model reconstructs the backbone of galaxies without ad-hoc assumptions of the underlying distribution functions, it has been widely used to uncover galaxies' underlying dark matter distributions (e.g., Cappellari et al 2006b;Yang et al 2020), central black hole mass (e.g., van der Marel et al 1998;Cretton & van den Bosch 1999;Verolme et al 2002;Gebhardt et al 2003;Valluri et al 2004;Krajnović et al 2009;Ahn et al 2018;Thater et al 2022b), and internal stellar orbit distributions (e.g., Zhu et al 2018a,b;Jin et al 2020). Recently it has been modified to include the barred structures explicitly, thus also for uncovering the bar pattern speed (Vasiliev & Valluri 2020;Tahmasebzadeh et al 2022).…”