Applying Schwarzschild's orbit superposition method to barred or non-barred disc galaxies

TL;DR

This paper advances Schwarzschild's orbit superposition method to model both barred and non-barred disc galaxies, including elliptical galaxies with figure rotation, improving model stability and applicability.

Contribution

It introduces enhancements to the SMILE code for better potential representation and rotation handling, enabling more accurate equilibrium models of complex galaxy structures.

Findings

Models of elliptical galaxies with figure rotation are stable over many dynamical times.

Constructed models of barred disc galaxies with analytic potentials are not self-consistent.

Reconstructed models from N-body snapshots are in near-stationary state, unlike original simulations.

Abstract

We present an implementation of the Schwarzschild orbit superposition method which can be used for constructing self-consistent equilibrium models of barred or non-barred disc galaxies, or of elliptical galaxies with figure rotation. This is a further development of the publicly available code SMILE; its main improvements include a new efficient representation of an arbitrary gravitational potential using two-dimensional spline interpolation of Fourier coefficients in the meridional plane, as well as the ability to deal with rotation of the density profile and with multicomponent mass models. We compare several published methods for constructing composite axisymmetric disc--bulge--halo models and demonstrate that our code produces the models that are closest to equilibrium. We also apply it to create models of triaxial elliptical galaxies with cuspy density profiles and figure rotation, and find that such models can be found and are stable over many dynamical times in a wide range of pattern speeds and angular momenta, covering both slow- and fast-rotator classes. We then attempt to create models of strongly barred disc galaxies, using an analytic three-component potential, and find that it is not possible to make a stable dynamically self-consistent model for this density profile. Finally, we take snapshots of two N-body simulations of barred disc galaxies embedded in nearly-spherical haloes, and construct equilibrium models using only information on the density profile of the snapshots. We demonstrate that such reconstructed models are in near-stationary state, in contrast with the original N-body simulations, one of which displayed significant secular evolution.