Dwarf-Finding Procedure

Bound objects are found by a `friends-of-friends' algorithm. Lists of candidate objects are generated for a range of linking lengths bcrit. These are combined to produce two master catalogs of nearly virialized objects (0.3 < -T/U < 0.7); the `inclusive' and `exclusive' catalogs use the largest and smallest bcrit values which satisfy the above constraint on T/U.

First, a friends-of-friends algorithm identifies contiguous regions in which each pair of bodies can be connected by a path, passing through their neighbors, with maximum step length less than bcrit. Second, the binding energy of each body in each such region is evaluated, and unbound bodies are deleted; this process is repeated until convergence. Regions which lose more than 20% of their bodies during this culling process are excluded from further consideration. Third, regions with net binding energy T+U < 0 are designated as candidate dwarfs. The result is a distinct catalog for each value of bcrit.

bcrit = 0.010 bcrit = 0.014 bcrit = 0.020
bcrit = 0.028 bcrit = 0.040 bcrit = 0.057
bcrit = 0.080 bcrit = 0.113 bcrit = 0.160

Nine such dwarf catalogs, each derived for a different value of bcrit, are shown above. Bodies belonging to dwarfs are shown in colors, while other bodies are shown in grey. For the smallest values of bcrit, only a few scattered regions are colored. Larger values of bcrit link up larger regions. Eventually, the linkage percolates along most of the tails; such large regions are rejected as candidate dwarfs since they are not gravitationally bound.

Joshua E. Barnes (barnes@ifa.hawaii.edu)
Last modified: March 2, 2001