This code uses the algorithm described 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 which might save you some time:
1- Using this method, some combinations of component masses lead the dark matter halo to be unrelaxated near the very center of the galaxy. If that is the case for your galaxy, you will see a ring appearing in its stellar disk in less than one rotation time. When that happens, I like to relaxate the halo for a few hundred Myr while keeping the other components frozen (both Gadget2 and RAMSES can do that) in order to ensure a good state of equilibrium.
2- 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.
3- The vertical equilibrium of the gas component depends on your simulation setup. If you use radiative cooling, it will settle on a very short timescale (a few tens of Myr at most). If not, it will take about one rotation period to reach equilibrium.
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
- h5py (only if you need the HDF5 file format, python-h5py)
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] [-cores CORES] [--force-yes] [--force-no] [--hdf5]
[-o init.dat] [-i params_galaxy.ini]
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
-cores CORES The number of cores to use during the potential
canculation. Make sure this number is a factor of
N_rho*N_z. Default is 1.
--force-yes Don't ask if you want to use the existing
potential_data.txt file. Useful for automating the
execution of the script.
--force-no Same as above, but with the opposite effect.
--hdf5 Output initial conditions in HDF5 format.
-o init.dat The name of the output file.
-i params_galaxy.ini The name of the .ini file.
If you are getting OSError: [Errno 24] Too many open files while trying to run this code in OSX, please try this.
Feel free to use this code in your work, but please link this page in your paper.