Charlie Mace

Charlie Mace

he/him

Research

N-body Simulations

Most of my PhD work has focused on N-body simulations of self-interacting dark matter (SIDM). I have published a study on numerical convergence in SIDM N-body simulations, where I present choices for particle resolution, timestep size, and gravitational softening length that minimize numerical errors. In this study I found energy non-conservation issues that are still not fully understood in SIDM simulations, and I am investigating these issues in more detail for a future study. The simulation data used in this study are publicly available here.

A 4 panel figure showing collapse time convergence as a function of numerical resolution. SIDM core-collapse time converging as a function of particle number N.

In my most recent publication I use these N-body simulations to calibrate models for gravothermal core-collapse. This calibrate allows for quick calculation of the dark matter density profile at any point in time, without the need to run N-body simulations.

Some of my ongoing and future work with SIDM N-body simulations includes:

  1. Using the N-body/hydrodynamical simulation GIZMO to model bullet cluster analogs
  2. Working with other OSU graduate students to investigate how tidal effects alter core-collapse
  3. Studying the underlying causes of numerical error in SIDM simulations

Gravitational Lensing

An example of how self-interacting dark matter affects the lensing convergence. The compact core-collapsed halos inside the lens and along the line-of-sight produce powerful lensing signals, creating a potential probe of dark matter physics. An example of how self-interacting dark matter affects the lensing convergence.

I also study the observational signatures of SIDM, specifically the effect of gravothermal core-collapse on substructure lensing. Core-collapsed halos are very compact objects and strong gravitational lenses. If a lensing galaxy has core-collapsed subhalos they can distort the image, and produce an observable probe of SIDM.

I am implementing the SIDM models calibrated by my N-body simulations into the lensing software package lenstronomy. My current project is using these models to test how observable the effects of SIDM on gravitational lenses would be, and testing different core-collapse models to determine the most efficient way to model SIDM halos in lensed systems. I presented preliminary results from this study at the 247th meeting of the American Astronomical Society, and expect to submit this paper by May 2026.