How D-type HII region expansion depends on numerical resolution

TL;DR

This study examines how the numerical resolution affects the simulation of D-type HII region expansion, revealing that adequate resolution is crucial for accurate modeling of their structure and momentum transfer.

Contribution

It demonstrates the resolution threshold needed to accurately simulate HII region expansion and its impact on feedback processes in astrophysical simulations.

Findings

Resolution with dr ≤ 0.3 R_st yields accurate structure and momentum.

Under-resolved simulations can misestimate radial momentum by factors up to 10.

Proper resolution is essential for realistic modeling of ionizing feedback.

Abstract

We investigate the resolution dependence of HII regions expanding past their Str\"{o}mgren spheres. We find that their structure and size, and the radial momentum that they attain at a given time, is in good agreement with analytical expectations if the Str\"{o}mgren radius is resolved with $dr \leq 0.3\,R_{\rm st}$. If this is not satisfied, the radial momentum may be over- or under-estimated by factors up to 10 or more. Our work has significance for the amount of radial momentum that a HII region can impart to the ambient medium in numerical simulations, and thus on the relative importance of ionizing feedback from massive stars.