next up previous
Next: Examples Up: PM Code Previous: How to get power

How to find halos using the Bound-Density-Maxima code

Run PMhalos. The code will ask you many questions. It will produce two files with the final results. ``Catalog.DAT'' contains detailed information about all halos found by the code. After a rather long preamble, data on the halos follow. Each halo has a ``header'', which gives global parameters: coordinates, velocities, mass, and so on for the halo (format is given in the preamble). ``Catshort.DAT'' has a shorter preamble and has only a list of the halo headers.

Tips: The code may miss some halos if one chooses wrong parameters!

The number of spheres (seeds) should be very large: 100,000 - 150,000. If it is too small, the code misses some of small halos (but not the big ones).
The number of particles in each shell for the halo profile should be large: 5-6 per shell. The code needs the density profile of a halo to find radius, escape velocity and so on. It may get confused if the profile is too noisy.
Radius of the first bin for the profile should not be too small: not less than 1/2 of your force resolution. It should also contain few particles ( > 2 ).
Outer radius should be large. If density does not decline enough (flat profile), the code thinks that this halo is a fluke. If your radius is too small such that only the central part of a potential halo fits in the radius, and the density gradient is not steep, the code will kill your halo.

next up previous
Next: Examples Up: PM Code Previous: How to get power
Jon Holtzman