Tensor classification of structure in smoothed particle hydrodynamics density fields

TL;DR

This paper introduces tensor classification as an effective, parameter-free method for identifying complex structures in smoothed particle hydrodynamics density fields, enhancing analysis of astrophysical simulations.

Contribution

It demonstrates tensor classification's ability to detect diverse structures in SPH simulations without free parameters, using native smoothing and multiple tensors.

Findings

Successfully identifies filaments, shells, and sheets in molecular cloud simulations.

Detects spiral arms in galactic discs.

Shows how different tensors reveal physical process interactions.

Abstract

As hydrodynamic simulations increase in scale and resolution, identifying structures with non-trivial geometries or regions of general interest becomes increasingly challenging. There is a growing need for algorithms that identify a variety of different features in a simulation without requiring a "by-eye" search. We present tensor classification as such a technique for smoothed particle hydrodynamics (SPH). These methods have already been used to great effect in N-Body cosmological simulations, which require smoothing defined as an input free parameter. We show that tensor classification successfully identifies a wide range of structures in SPH density fields using its native smoothing, removing a free parameter from the analysis and preventing the need for tesselation of the density field, as required by some classification algorithms. As examples, we show that tensor classification using the tidal tensor and the velocity shear tensor successfully identifies filaments, shells and sheet structures in giant molecular cloud simulations, as well as spiral arms in discs. The relationship between structures identified using different tensors illustrates how different forces compete and co-operate to produce the observed density field. We therefore advocate the use of multiple tensors to classify structure in SPH simulations, to shed light on the interplay of multiple physical processes.