科研之友
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摘要
We have developed a new halo- finding method called the physically self- bound ( PSB) group- finding algorithm, which is designed to identify halos located in crowded regions. To demarcate subhalo regions, we introduce the tidal constraint combined with the self- boundedness check. In order to reduce overload and parallel finding, we first divide whole simulation particles into many local particle groups using two distinct methods. One adopts a density mesh used to group particles in connected local overdense cells, and the other applies the friends- of- friends ( FoF) algorithm with a linking length ( l(loc)) 0.3 times the mean particle separation. Then we divide each local particle group into several subgroups enclosed by numerous density levels and identify tidally stable and self- bound subhalos around density peaks. Subhalo finding is done on a fine mesh with cell size equal to twice the force resolution. Particles in a density shell that surrounds only one density peak form a subhalo candidate. Particles located in the outer remaining density shells that surround more than one peak become member candidates of one of the subhalos. We determine the membership using the tidal boundary constraint. We have found that the mass function is very insensitive to l(loc) when l(loc) >= 0: 3. At least 40% of subhalos do not seem to collapse to the most massive subhalo in a FoF group when the Press & Schechter collapse model is applied to measure the size of a collapsed structure in the Lagrangian space. We have applied our halo- finding method to a 1024(3) particle simulation in a Lambda CDM model and compare the halo mass functions with those previously found in the literature.
- 出版日期2006-3-10
