Star Formation and Feedback in Smoothed Particle Hydrodynamic Simulations II: Resolution Effects

TL;DR

This study investigates how mass and force resolution in smoothed particle hydrodynamics simulations affect star formation, feedback, and galaxy structure, providing guidelines for accurate modeling of isolated galaxies across a range of masses.

Contribution

It offers specific resolution recommendations for simulating star formation and feedback, highlighting the impact of resolution on galaxy morphology and feedback processes.

Findings

High resolution (at least 10^4 particles per component) is necessary for accurate global star formation.

Low mass resolution weakens stellar disks due to two-body heating effects.

Galaxies around 10^10 solar masses are highly sensitive to resolution changes, affecting feedback and disk formation.

Abstract

We examine the effect of mass and force resolution on a specific star formation (SF) recipe using a set of N-body/Smooth Particle Hydrodynamic simulations of isolated galaxies. Our simulations span halo masses from 10^9 to 10^13 solar masses, more than four orders of magnitude in mass resolution, and two orders of magnitude in the gravitational softening length, epsilon, representing the force resolution. We examine the total global star formation rate, the star formation history, and the quantity of stellar feedback and compare the disk structure of the galaxies. Based on our analysis, we recommend using at least 10^4 particles each for the dark matter and gas component and a force resolution of epsilon approximately equal to 10^-3 R_vir when studying global SF and feedback. When the spatial distribution of stars is important, the number of gas and dark matter particles must be increased to at least 10^5 of each. Low mass resolution simulations with fixed softening lengths show particularly weak stellar disks due to two-body heating. While decreasing spatial resolution in low mass resolution simulations limits two-body effects, density and potential gradients cannot be sustained. Regardless of the softening, low-mass resolution simulations contain fewer high density regions where SF may occur. Galaxies of approximately 10^10 solar masses display unique sensitivity to both mass and force resolution. This mass of galaxy has a shallow potential and is on the verge of forming a disk. The combination of these factors give this galaxy the potential for strong gas outflows driven by supernova feedback and make it particularly sensitive to any changes to the simulation parameters.