Gaseous Dynamical Friction: a Numerical Study of Extended Perturbers

TL;DR

This study uses high-resolution simulations to analyze gaseous dynamical friction on extended perturbers, revealing that standard models may overestimate drag forces, especially near Mach 1, with implications for galaxy cluster dynamics.

Contribution

The paper provides the first detailed numerical analysis of gaseous dynamical friction on extended bodies, comparing multiple hydrodynamics solvers and identifying conditions for accurate force recovery.

Findings

Wake structure and drag force are accurately recovered beyond 4 times the perturber's softening radius.

Standard linear point mass solutions overestimate drag by up to 25% near Mach 1.

Dynamical friction is linear for subhaloes in less massive haloes but becomes non-linear in more massive environments.

Abstract

The process of momentum and energy transfer between a massive body and a background medium it is moving through is known as dynamical friction (DF). It is key to our understanding of many astrophysical systems. We present a series of high-resolution simulations of gaseous DF using Lagrangian meshless finite mass hydrodynamics solver, the moving-mesh MUSCL scheme, and the piecewise parabolic method (PPM) solver. We use a set of simulations of massive bodies, modelled as Plummer spheres, moving with Mach $0.2 \leq \mathcal{M} \leq 3$. We investigate at which radial distances from the perturber these solvers recover the linear point mass solution for gaseous DF. We analyse the drag force and the structure and time evolution of the wake. The different solvers agree closely. Numerical convergence is reached when the initial spatial resolution is $0.2r_s$, where $r_s$ is the softening scale of the Plummer sphere. We find that the wake structure and drag force are recovered, at the $5\%$ level, when compared beyond $4r_\mathrm{s}$. Our results predict that models using the standard linear point mass DF solution will overestimate the drag force on extended perturbers by as much as 25\%, for Mach$\sim$1. Finally, we consider DF in the context of galaxy clusters, where dark matter subhaloes move through circumgalactic media. We show that DF is typically in the linear regime for most subhaloes in hosting haloes $<10^{11}$ M$_{\odot}$ but non-linear in more massive host haloes.