STAR FORMATION AND FEEDBACK IN SMOOTHED PARTICLE HYDRODYNAMIC SIMULATIONS. II. RESOLUTION EFFECTS
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abstract
We examine the effect of mass and force resolution on a specific star
formation (SF) recipe using a set of N-body/Smooth Particle Hydrodynamic
simulations of isolated galaxies. Our simulations span halo masses from 10^9 to
10^13 solar masses, more than four orders of magnitude in mass resolution, and
two orders of magnitude in the gravitational softening length, epsilon,
representing the force resolution. We examine the total global star formation
rate, the star formation history, and the quantity of stellar feedback and
compare the disk structure of the galaxies. Based on our analysis, we recommend
using at least 10^4 particles each for the dark matter and gas component and a
force resolution of epsilon approximately equal to 10^-3 R_vir when studying
global SF and feedback. When the spatial distribution of stars is important,
the number of gas and dark matter particles must be increased to at least 10^5
of each. Low mass resolution simulations with fixed softening lengths show
particularly weak stellar disks due to two-body heating. While decreasing
spatial resolution in low mass resolution simulations limits two-body effects,
density and potential gradients cannot be sustained. Regardless of the
softening, low-mass resolution simulations contain fewer high density regions
where SF may occur. Galaxies of approximately 10^10 solar masses display unique
sensitivity to both mass and force resolution. This mass of galaxy has a
shallow potential and is on the verge of forming a disk. The combination of
these factors give this galaxy the potential for strong gas outflows driven by
supernova feedback and make it particularly sensitive to any changes to the
simulation parameters.
