Resolution requirements for simulating gravitational fragmentation using SPH

School of Physics & Astronomy, Cardiff University, 5 The Parade, Cardiff CF24 3YB, Wales, UK e-mail: David.Hubber@astro.cf.ac.uk

Received: 24 August 2005
Accepted: 1 December 2005

Abstract

Jeans showed analytically that, in an infinite uniform-density isothermal gas, plane-wave perturbations collapse to dense sheets if their wavelength, λ, satisfies (where a is the isothermal sound speed and is the unperturbed density); in contrast, perturbations with smaller λ oscillate about the uniform density state. Here we show that Smoothed Particle Hydrodynamics reproduces these results well, even when the diameters of the SPH particles are twice the wavelength of the perturbation. Our simulations are performed in 3-D with initially settled (i.e. non-crystalline) distributions of particles. Therefore there exists the seed noise for artificial fragmentation, but it does not occur. We conclude that, although there may be – as with any numerical scheme – “skeletons in the SPH cupboard”, a propensity to fragment artificially is evidently not one of them.