A demonstration of Enhanced Halo Resolution
The Tempest Simulations are a series of cosmological "zoom" hydrodynamics simulations following the evolution of a Milky Way mass galaxy from just after the Big Bang to present day. Unlike most traditional simulations, they employ Enhanced Halo Resolution (EHR), a technique to assure that the outskirts of the target galaxy resolve small spatial scales. As you will witness, this is important for the physical modeling of the gas throughout the galactic volume.
This movie shows two galaxies taken from the Tempest Simulations, identical aside from their differences in spatial resolution. The galaxy on the left uses a traditional resolution scheme (AMR) only able to resolve at a coarse 4 comoving kpc near the virial radius, whereas the galaxy on the right employs the new Enhanced Halo Resolution (EHR) scheme requiring spatial resolution elements to be no larger than 500 comoving parsecs (16x better) throughout the halo.
The movie displays neutral hydrogen (H I) column density maps for each galaxy. H I is typically a tracer of cool, dense gas. These views are projected face-on to the galactic disk. Both simulations accrete the same cosmological structures: cool filamentary inflows and merging galaxies. But the EHR scheme results in substantially more H I, increasingly found in smaller, denser clouds able to survive for longer. The excess H I in the EHR simulation on the right arises from two sources: efficient cooling out of existing structures (i.e., precipitation), and preservation against the effects of artificial mixing that occur when gas is underresolved. For more information about the Tempest Simulations and the effects of EHR on galaxy evolution, please read our paper: Hummels et al. 2019 .
For more on EHR and the Tempest Simulations, please visit: chummels.org/tempest .