Effects of Spatial Discretization in Lyman-alpha Line Radiation Transfer Simulations

TL;DR

This paper investigates how different spatial discretization methods and resolutions impact the accuracy of Lyman-alpha line transfer simulations, revealing significant dependencies that affect the reliability of synthetic observations.

Contribution

It introduces Lyman-alpha line transfer into the SKIRT code and systematically studies the influence of various spatial grid types and resolutions on simulation results.

Findings

Lyman-alpha line profiles strongly depend on grid type and resolution.

Under-resolved hydrogen density gradients lead to unreliable results.

Further research needed to determine necessary spatial resolution for accurate modeling.

Abstract

We describe the addition of Lyman-alpha resonant line transfer to our dust continuum radiation transfer code SKIRT, verifying our implementation with published results for spherical problems and using some self-designed three-dimensional setups. We specifically test spatial discretization through various grid types, including hierarchical octree grids and unstructured Voronoi tessellations. We then use a radiation transfer post-processing model for one of the spiral galaxies produced by the Auriga cosmological zoom simulations to investigate the effect of spatial discretization on the synthetic observations. We find that the calculated Lyman-alpha line profiles exhibit an extraordinarily strong dependence on the type and resolution of the spatial grid, rendering the results untrustworthy at best. We attribute this effect to the large gradients in the hydrogen density distribution over small distances, which remain significantly under-resolved in the input model. We therefore argue that further research is needed to determine the required spatial resolution of a hydrodynamical simulation snapshot to enable meaningful Lyman-alpha line transfer post-processing.