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Living on the edge. A quantitative warning on boundary artifacts in the IllustrisTNG

Ana Mitrašinović

TL;DR

This paper addresses the problem that periodic boundary conditions in cosmological simulations can introduce numerical artifacts that masquerade as physical phenomena. The authors analyze the IllustrisTNG suite using a lower stellar mass cut $M_\star > 10^{8.5} M_\odot$ and a dark-matter-to-baryon criterion $M_\mathrm{DM} < 2 M_\mathrm{B}$ to identify dark-matter-deprived galaxies (DMDGs) as artifacts. They find that artifact prevalence scales inversely with box size, exhibits strong edge concentration, and demonstrate a boundary-crossing mass-loss artefact, then propose mitigation such as sanity checks and excluding a buffer region of about $1$–$2$ cMpc/h. These results guide robust use of IllustrisTNG data, highlighting which volumes and regions require extra caution.

Abstract

Periodic boundary conditions (PBCs) are a practical necessity in cosmological simulations, but they can also introduce numerical artifacts. We quantified the prevalence of PBC-related artifacts in the IllustrisTNG using dark-matter-deprived galaxies (DMDGs) as tracers. We found that their occurrence scales inversely with simulation volume. We demonstrated that this excess population is spatially correlated with the box edges; the smallest TNG50 box is most affected by these problems. This is a unique and irreplaceable resource for studying galaxy structure. Manual inspection confirmed abrupt, unphysical mass-loss events coincident with boundary crossings. We also highlight the challenge of disentangling numerical artifacts from genuine tidally stripped galaxies in boundary-crossing clusters in TNG100. We conclude by recommending a set of mandatory sanity checks that include positional verification, mass history analysis, and even exclusion of the buffer zone near the edges. These strategies ensure the robustness of the scientific results derived from these invaluable simulations.

Living on the edge. A quantitative warning on boundary artifacts in the IllustrisTNG

TL;DR

This paper addresses the problem that periodic boundary conditions in cosmological simulations can introduce numerical artifacts that masquerade as physical phenomena. The authors analyze the IllustrisTNG suite using a lower stellar mass cut and a dark-matter-to-baryon criterion to identify dark-matter-deprived galaxies (DMDGs) as artifacts. They find that artifact prevalence scales inversely with box size, exhibits strong edge concentration, and demonstrate a boundary-crossing mass-loss artefact, then propose mitigation such as sanity checks and excluding a buffer region of about – cMpc/h. These results guide robust use of IllustrisTNG data, highlighting which volumes and regions require extra caution.

Abstract

Periodic boundary conditions (PBCs) are a practical necessity in cosmological simulations, but they can also introduce numerical artifacts. We quantified the prevalence of PBC-related artifacts in the IllustrisTNG using dark-matter-deprived galaxies (DMDGs) as tracers. We found that their occurrence scales inversely with simulation volume. We demonstrated that this excess population is spatially correlated with the box edges; the smallest TNG50 box is most affected by these problems. This is a unique and irreplaceable resource for studying galaxy structure. Manual inspection confirmed abrupt, unphysical mass-loss events coincident with boundary crossings. We also highlight the challenge of disentangling numerical artifacts from genuine tidally stripped galaxies in boundary-crossing clusters in TNG100. We conclude by recommending a set of mandatory sanity checks that include positional verification, mass history analysis, and even exclusion of the buffer zone near the edges. These strategies ensure the robustness of the scientific results derived from these invaluable simulations.

Paper Structure

This paper contains 6 sections, 1 figure, 1 table.

Table of Contents

  1. Introduction
  2. Simulations
  3. Results
  4. Visual example of a boundary-crossing artifact
  5. A rigorous analysis of the boundary region
  6. Discussion and conclusion

Figures (1)

  • Figure 1: Illustrative example of a numerical artifact in TNG50. The total mass evolution of the galaxy is shown by the red line (right y-axis), and its relevant coordinate $y$ is shown by the blue dots (left y-axis). A sudden, unphysical mass-loss event is clearly visible and annotated as a PBC-related issue. This event coincides with the moment in which the galaxy approached the boundary, slightly before the boundary-crossing event.