On the robustness of triaxial Schwarzschild modelling: The effects of correcting the orbit mirroring

TL;DR

This study assesses the impact of a bug in the orbit mirroring procedure of a widely used triaxial Schwarzschild galaxy modeling code, finding that previous scientific results remain largely unaffected.

Contribution

We fixed a bug in the orbit mirroring procedure of the DYNAMITE code and quantified its effects on galaxy dynamical analyses.

Findings

Differences between original and corrected code results are negligible within uncertainties.

Previous results using the original code are not significantly affected by the bug.

The correction does not alter key galaxy property estimates such as black hole mass and intrinsic shape.

Abstract

In the past 15 years, the triaxial Schwarzschild orbit-superposition code by van den Bosch et al. (2008) has been widely applied to study the dynamics of galaxies. Recently, Quenneville et al. (2022) reported a bug in the orbit calculation of this code, specifically in the mirroring procedure that is used to speed up the computation. We have fixed the incorrect mirroring in DYNAMITE, which is the publicly-released successor of the triaxial Schwarzschild code by van den Bosch et al. (2008). In this study, we provide a thorough quantification of how this bug has affected the results of dynamical analyses performed with this code. We compare results obtained with the original and corrected versions of DYNAMITE, and discuss the differences in the phase-space distribution of a single orbit and in the global stellar orbit distribution, in the mass estimate of the central black hole in the highly triaxial galaxy PGC 46832, and in the measurement of intrinsic shape and enclosed mass for more than 50 galaxies. Focusing on the typical scientific applications of a Schwarzschild triaxial code, in all our tests we find that differences are negligible with respect to the statistical and systematic uncertainties. We conclude that previous results with the van den Bosch et al. (2008) triaxial Schwarzschild code are not significantly affected by the incorrect mirroring.