next up previous
Next: Rejection based on binding Up: The Friends of Friends Previous: The Friends of Friends

Rejecting halos based on the minimum number of friends, tex2html_wrap_inline2032

We suggest here a simple improvement. Replace tex2html_wrap_inline1958 with a new parameter, tex2html_wrap_inline2032, and only accept halos that have at least one particle with at least tex2html_wrap_inline2032 friends. The advantage of tex2html_wrap_inline2032 over tex2html_wrap_inline1958 is that diffuse, relatively low-density linked groups are more likely to be rejected, while small but compact clumps may still be accepted as real halos. The effects of tex2html_wrap_inline2032 in Model 3 are shown in the left hand panels of Figure 3, using tex2html_wrap_inline2046.

Figure: As Figure 2, but using the two alternative methods for rejecting spurious halos as discussed in the text. On the left are results for tex2html_wrap_inline2046, and on the right are results using the evaporative method. The evaporative method finds 11 halos, all of which are guaranteed (by construction) to be gravitationally bound. In contrast the method with tex2html_wrap_inline2046 requires much less computation, but finds only 8 halos (not as good as the evaporative method, but better than the conventional tex2html_wrap_inline1958 method, see Figure 2).

In this case all of the spurious halos are rejected, and more real halos are accepted than for tex2html_wrap_inline1958 = 30.

John Salmon
Sat Sep 27 18:44:36 PDT 1997