# The impact of numerical oversteepening on the fragmentation boundary in self-gravitating disks

## TL;DR

This study shows that the choice of numerical limiters in simulations of self-gravitating disks significantly affects the predicted fragmentation boundary, with oversteepening leading to overestimated surface densities and shifted fragmentation criteria.

## Contribution

It demonstrates how numerical oversteepening influences fragmentation boundaries in self-gravitating disk simulations, highlighting the importance of limiter choice in accurate modeling.

## Key findings

- Inappropriate limiters cause overestimation of surface density.
- Oversteepening effect amplifies over dynamical timescales.
- Fragmentation boundary shifts to larger cooling timescales.

## Abstract

Context. It is still an open issue whether a self-gravitating accretion disk fragments. There are many different physical and numerical explanations for fragmentation, but simulations often show a non-convergent behavior for ever better resolution. Aims. We investigate the influence of different numerical limiters in Godunov type schemes on the fragmentation boundary in self- gravitating disks. Methods. We compare the linear and non-linear outcome in two-dimensional shearingsheet simulations using the VANLEER and the SUPERBEE limiter. Results. We show that choosing inappropriate limiting functions to handle shock-capturing in Godunov type schemes can lead to an overestimation of the surface density in regions with shallow density gradients. The effect amplifies itself on timescales comparable to the dynamical timescale even at high resolutions. This is exactly the environment, where clumps are expected to form. The effect is present without, but scaled up by, self-gravity and also does not depend on cooling. Moreover it can be backtracked to a well known effect called oversteepening. If the effect is also observed in the linear case, the fragmentation limit is shifted to larger values of the critical cooling timescale.