The effect of star formation algorithms on the morphology of isolated galactic disc models

Abstract

Structure is found in the Universe on various scales ranging from galaxies to galaxy clusters, super clusters. . .This structure is believed to have formed in a bottom-up hierarchical way. Computational techniques allow us to model structure formation and improve our understanding of structure formation. Moreover, cosmological simulations and simulations of galaxy formation and evolution have resolutions orders of magnitude higher than the scales at which stars form. Therefore, the application of a convergent flow criterion in galaxy formation simulations is debatable. Two isolated galactic discs (280,000 particles each) and two collapsing clouds (with a NFW dark matter density profile, 100,000 particles each) were simulated for 1.02Gyr and 4.4Gyr respectively. Each pair of simulations differed in the star formation conditions. One model allowed star formation in collapsing regions only (negative velocity divergence), while the other had no such condition. Although both models had similar star formation rates, the two models also showed significant morphological differences. With the removal of the velocity divergence criterion more stars were formed and a wider spread in the stellar spatial distribution in the potential well was detected. The removal of the divergence criterion also limited the highest allowed gas densities, and populated the halo with hot diffuse gas due to shock heating and the feedback processes. More work, particularly simulations that begin from cosmological initial conditions, is required to better understand the impact of the divergence criterion.