The Accuracy of Subhalo Detection
  With the ever increasing resolution of N-body simulations, accurate subhalo
detection is becoming essential in the study of the formation of structure, the
production of merger trees and the seeding of semi-analytic models. To
investigate the state of halo finders, we compare two different approaches to
detecting subhaloes; the first based on overdensities in a halo and the second
being adaptive mesh refinement. A set of stable mock NFW dark matter haloes
were produced and a subhalo was placed at different radii within a larger halo.
SUBFIND (a Friends-of-Friends based finder) and AHF (an adaptive mesh based
finder) were employed to recover the subhalo. As expected, we found that the
mass of the subhalo recovered by SUBFIND has a strong dependence on the radial
position and that neither halo finder can accurately recover the subhalo when
it is very near the centre of the halo. This radial dependence is shown to be
related to the subhalo being truncated by the background density of the halo
and originates due to the subhalo being defined as an overdensity. If the
subhalo size is instead determined using the peak of the circular velocity
profile, a much more stable value is recovered. The downside to this is that
the maximum circular velocity is a poor measure of stripping and is affected by
resolution. For future halo finders to recover all the particles in a subhalo,
a search of phase space will need to be introduced.
