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This code uses the algorithm found in Springel, Di Matteo & Hernquist (2005) for generating the initial conditions for a disk galaxy simulation with the codes GADGET-2 or RAMSES (using the DICE patch), including a stellar disk, a gaseous disk, a dark matter halo and a stellar bulge. The first two components follow an exponential density profile, and the last two a Dehnen density profile with gamma=1 by default, corresponding to a Hernquist profile. You can check out the expressions in Ruggiero & Lima Neto (2017).

Some notes: this method fails to generate low mass halos (~10^10 solar masses) in equilibrium, since the velocity distribution for these near the center is strongly non gaussian. Secondly, if you run GADGET-2 without any gas cooling, the gaseous disk will gain lots of energy over time due to the artificial viscosity, and will get a lot thicker. Lastly, the gas component must me relaxed for a few hundred Myr to reach equilibrium in case your simulation doesn't include radiative cooling. If it does, relaxation will be a lot faster (a few tens of Myr at most).

About units: the value for the gravitational constant G used in this code is such that the unit for length is 1.0 kpc, for mass 1.0e10 solar masses, and for velocity 1.0 km/s. This is the default for GADGET-2, and works out of the box in RAMSES with the DICE patch.

• NumPy (python-numpy)
• SciPy (python-scipy)
• pyGadgetReader

You can run python galstep.py --help to see the message below. Also please check out the galaxy_params.ini file to see the available free parameters.

usage: galstep.py [-h] [--nogas] [-cores CORES] [--force-yes] [-o init.dat]

Generates an initial conditions file for a galaxy simulation with halo,
stellar disk, gaseous disk and bulge components.

optional arguments:
  -h, --help    show this help message and exit
  --nogas       Generates a galaxy without gas.
  -cores CORES  The number of cores to use during the potential canculation.
                Make sure this number is a factor of N_rho*N_z.
  --force-yes   Don't ask if you want to use the existing potential_data.txt
                file. Useful for automating the execution of the script.
  -o init.dat   The name of the output file.

If you are getting OSError: [Errno 24] Too many open files while trying to run this code in OSX, please try this.

• Ruggiero & Lima Neto (2017)

Rafael Ruggiero
Ph.D student at Universidade de São Paulo (USP), Brazil
Contact: rafael.ruggiero [at] usp.br

Feel free to use this code in your work, but please link this page in your paper.