GADGET 2 IC (Initial Condition) README

These two codes are required to generate new initial condition (IC) code for GADGET-2.

1. MW: To create a single Milky Way-liked galaxy with dark matter halo, gas, disk, and bulge particles.
2. CombineGalaxies: To combine two galaxies together to create merging scenario

Installation

• Change 'Makefile' in MW/ and 'makefile' in CombineGalaxies/ to be suitable for your machine.

Usage

MW

• make clean :To clear previous complied files
• make: To compile the code. The code is needed to be compiled everytime the parameters are changed in main.c.
• ./MakeHubbleType galaxy.dat: To run with code with <output_name> (galaxy.dat).

All important parameters are in main.c. The important parameters to be changed include

N_HALO=   10000;        /* desired number of particles in dark halo */
N_DISK=   5000;        /* desired number of collisionless particles in disk */
N_GAS=    10000;        /* number of gas particles in disk */ 
N_BULGE=  0;        /* number of bulge particles */ 

CombineGalaxies

• make clean and then make to compile the code.
• ./CombineGalaxies galaxy.dat 0 45 galaxy.dat 90 0 50 300 0.2 combine_gal.dat

./CombineGalaxies <fname_gal1> <theta1> <phi1> <fname_gal2> <theta2> <phi2> <rmin> <rstart> <eccentricity> <fname_galout>
(angles in degrees.)

• <iso_galaxy_1/2>: the isolated galaxy ICs
• <theta1/2>: the spherical ‘theta’ values that the angular momentum of galaxy 1/2 is offset from the angular momentum vector of the orbit
• <phi1/2>: the spherical ‘phi’ values that the angular momentum of galaxy 1/2
• <r_min>: the (keplarian calculated) pericenter passage distance
• <r_start>: the initial offset of the two galaxies
• : eccentricity of the orbit
• <fname_galout>: output name "name.dat"

To include gas in your simulation

The default file that I have in here has no gas. To be able to run simulation with gas, you will need to edit main.c file to include the gas.

1. Uncomment these three lines in main.c so that the code can calculate the number of gas in the simulation.

  // N_GAS_DISK = N_GAS;
  // N_GAS_FLOW = (int)(ColdFlowExtraMgas/(M_GAS/((float)N_GAS_DISK)));
  // N_GAS = N_GAS_DISK + N_GAS_FLOW;

2. Change these parameters to include the gas. (M_GAS = 0.900, N_GAS to the same as N_HALO)

M_GAS  = 0.000;   		/* total gas mass in units of 10^10 Msolar */
N_GAS  =    0;        /* number of gas particles in disk */ 

Don't forget to complie again before running the new version

Additional Information about Gadget 2

There are several formats of the output that you can use. I would recommend using hdf5 (SnapFormat = 3), which means that you will have to install Gadget 2 with HDF5 module, so that you can actually use this file format.

Good luck!