Abstract
We provide detailed comparison between the AMR code Enzo-2.4 and the SPH code
GADGET-3 in the context of direct baryonic collapse within DM halos to form
supermassive black hole (SMBH) seeds, in isolated and cosmological frameworks,
at z ~ 10-20. We find that both codes show an overall agreement in the general
features of the collapse, however, many subtle differences exist. For isolated
models, we find that the codes increase their spatial and mass resolutions at
different pace, leading to substantially earlier collapse times in SPH due to
higher gravitational resolution in GADGET-3. In fully cosmological runs,
starting from z = 200, the AMR develops a slightly higher baryonic resolution
than SPH during DM halo growth via cold accretion permeated by mergers. Still,
both numerical schemes agree in the buildup of DM and baryonic structures.
However, with the onset of direct collapse, this difference in mass and spatial
resolution is amplified, so the evolution of SPH models begins to lag behind
the AMR by ~10-20 Myr, especially in the central regions of halos. Such a delay
can, in principle, have an effect on formation/destruction rate of molecular
hydrogen in the presence of UV background, and on basic properties of host DM
halos. Finally, the isolated models in spinning DM halos, with cosmological
spin parameter lambda ~ 0.01 - 0.07, show delayed collapse times for greater
lambda, but the pace of this increase is faster for the AMR. This conclusion
does not stand for cosmological models. Within our simulation setup, GADGET-3
requires significantly larger computational resources than Enzo-2.4 during the
collapse stage, cosmological or isolated, and needs similar resources, within
factor ~2, during the pre-collapse, cosmological structure formation phase. Yet
it benefits from substantially higher force and hydrodynamic resolution, except
near the end of the collapse.
Description
[1512.03822] Direct Collapse to Supermassive Black Hole Seeds: Comparing the AMR and SPH Approaches
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