Classifying and modelling spiral structures in hydrodynamic simulations of astrophysical discs

TL;DR

This paper introduces numerical techniques for automatically identifying and modeling spiral arms in hydrodynamic simulations of astrophysical discs, enabling detailed analysis of spiral structures and their properties.

Contribution

The authors develop a method to fit individual spiral arms in simulations, including measurements of pitch angle, width, and pattern speed, applicable to various hydrodynamics systems.

Findings

Effective detection of spiral arms in flocculent patterns

Accurate estimation of pitch angles and arm widths

Method applicable to any finite-element hydrodynamics system

Abstract

We demonstrate numerical techniques for automatic identification of individual spiral arms in hydrodynamic simulations of astrophysical discs. Building on our earlier work, which used tensor classification to identify regions that were "spiral-like", we can now obtain fits to spirals for individual arm elements. We show this process can even detect spirals in relatively flocculent spiral patterns, but the resulting fits to logarithmic "grand-design" spirals are less robust. Our methods not only permit the estimation of pitch angles, but also direct measurements of the spiral arm width and pattern speed. In principle, our techniques will allow the tracking of material as it passes through an arm. Our demonstration uses smoothed particle hydrodynamics simulations, but we stress that the method is suitable for any finite-element hydrodynamics system. We anticipate our techniques will be essential to studies of star formation in disc galaxies, and attempts to find the origin of recently observed spiral structure in protostellar discs.