A library of hybrid N-body + test particle simulations for dynamical modeling of galaxy interactions. These are intended for use within the Identikit environment.

This repository consists of bulge+disk+NFW halo galaxy models to facilitate exploration of encounters with various mass ratios. The "full mass" and "half mass" models are the same as those provided by Barnes & Hibbard (2009) and the makefiles are essentially identical to those provided with Identikit, but separated into different files.

The "quarter mass" and "eighth mass" models have been created by George Privon. These models were computed by further reducing the scale lengths by a factor sqrt(2) for each halving of the mass.

The initial conditions files given below provide sample encounters for parabolic orbits and a variety of pericenter seperations.

Constructing the initial conditions and running these simulations requires installation of the Zeno N-body/SPH simulation environment (github link).

The initial conditions files and run files follow a naming convention of IdkZYX and IdkZYXrun, where the numbers replacing ZYX correspond to:

• Z = 1 indicating parabolic orbits.
• Y indicating the sum of the fractional masses of the interacting galaxies. 2 indicates an equal-mass encounter (1+1) while 5 indicates a 1:4 mass ratio (1+4).
• X indicates the pericenter separation at first pass, for the idealized Keplerian orbit. This corresponds to multiples of 1/16 simulation units.

Thus, Idk12X contains initial conditions for equal mass galaxy encounters on parabolic orbits. The file has a range of first pericenter encounters (1/16 through 16/16, in simulation units). The Idk12Xrun file contains routines to evolve the initial conditions for a suitable time range and save the snapshots for comparison with data.

• halo_... Halo mass profiles, accounting for the effects of gravitational softening.
• bulge_... Hernquist bulge mass profiles, accounting for the effects of gravitational softening.

Users of these models should cite Barnes & Hibbard (2009).