Merger Trees
Available below is fortran code to generate "merger trees"
describing the hierarchical growth of dark matter halos
using the method devised and implemented by Cedric Lacey
and Shaun Cole.
The Algorithm
A brief description of the algorithm can be found in
Cole, Lacey, Baugh and Frenk (MNRAS 2000) and
is reproduced
here . Cedric Lacey has made extensive comparsions with
N-body merger trees and finds very good statistical agreement.
The shortcoming is that if pushed hard to generate the very
high redhift (eg z>3) progenitors of present day halos it
tends to systematically underestimate the abundance of the
most massive progenitors. For most applications this can
be circumvented by starting the trees at say redshift $z=2$
when looking at z=3 progenitors.
The Code
The main subroutine is make_tree() and is quite well documented
in the header of the source code file
make_tree.f .
An example calling program and the
full set of source files needed to compile and link the code
are listed below.