Resolution Convergence in Cosmological Hydrodynamical Simulations Using Adaptive Mesh Refinement

TL;DR

This paper investigates how resolution affects gas distribution and star formation in cosmological hydrodynamical simulations using adaptive mesh refinement, highlighting the importance of initial conditions and introducing a new grid-hold-back method.

Contribution

It demonstrates the impact of resolution on simulation outcomes and presents a novel grid-hold-back approach to reduce star formation offsets.

Findings

AMR simulations show more small-scale power than fixed grid.

Star formation offsets of 10-20% persist at 1 kpc resolution.

Resolution of initial conditions influences structure formation.

Abstract

We have explored the evolution of gas distributions from cosmological simulations carried out using the RAMSES adaptive mesh refinement (AMR) code, to explore the effects of resolution on cosmological hydrodynamical simulations. It is vital to understand the effect of both the resolution of initial conditions and the final resolution of the simulation. Lower initial resolution simulations tend to produce smaller numbers of low mass structures. This will strongly affect the assembly history of objects, and has the same effect of simulating different cosmologies. The resolution of initial conditions is an important factor in simulations, even with a fixed maximum spatial resolution. The power spectrum of gas in simulations using AMR diverges strongly from the fixed grid approach - with more power on small scales in the AMR simulations - even at fixed physical resolution and also produces offsets in the star formation at specific epochs. This is because before certain times the upper grid levels are held back to maintain approximately fixed physical resolution, and to mimic the natural evolution of dark matter only simulations. Although the impact of hold back falls with increasing spatial and initial-condition resolutions, the offsets in the star formation remain down to a spatial resolution of 1 kpc. These offsets are of order of 10-20%, which is below the uncertainty in the implemented physics but are expected to affect the detailed properties of galaxies. We have implemented a new grid-hold-back approach to minimize the impact of hold back on the star formation rate.