Models of structure formation by gravitational clustering of `cold' dark matter predict that galaxy halos should contain a broad spectrum of substructure. These `subhalos' could perturb galactic disks and heat them to unacceptable levels. The self-consistent response of a dark halo may amplify the perturbations due to subhalos; here we use self-consistent N-body experiments to study this amplification effect and set limits on acceptable levels of halo substructure.

**Initial Data**The galaxy model used in these experiments has a central bulge, an exponential disk, and a spherical dark halo. Disk components are actually modeled in two different ways; as flat, rotating structures corresponding to the usual notion of a disk, or by spherical, isotropic distributions with the same cumulative mass profiles as an exponential disk. When the latter disk model is used, distribution functions for all components may be calculated exactly using Abel integrals.

**Test Runs**In our simulations, the orbits of bodies are perturbed by halo fluctuations and by the numerical approximations made in force calculation and orbital integration. The fluctuations are the effect we wish to study, while the numerical errors are artifacts which tend to mask the signal from the halo. Here, short calculations are used to determine the time-step and force-calculation parameters.

**Reference Run**Before running calculations with halo substructure, we measure the level of noise due to discreteness in the N-body representation.

**Disk Simulations**Here are some preliminary runs including real disks. It appears that satellites can indeed heat disks!

Joshua E. Barnes (barnes@ifa.hawaii.edu)

Last modified: May 8, 2002

`http://www.ifa.hawaii.edu/~barnes/research/halo_noise/index.html`