N-Body Data Archive

Here we list a few sample datasets (snapshot), which have been kindly donated by the authors. Most of the data will be in a format described with the data itself. Some work is being done on defining an N-body Data Interchange Format for such data, where we also make some sample data available.

Other N-Body Data Archives (excluding animations) that we know about :

NOTE: To retrieve the data through a WWW browser, you probably need to turn on some kind of option Load To local disk before you click on the datasets themself. ASCII files have normamlly been compressed with the GNU gzip program for sake of efficiency. In the examples below I have assumed that the zcat program is the version that correctly uncompresses .gz or .Z files.

Plummer (1911) models. Fun to test with, since they are equilibrium models.
Lecar (1968) , the IAU-25 body problem.
Sellwood (1993) A Bar model for the Galactic Bulge .
F.Governato, M.Colpi and L.Maraschi (1994) The fate of central black holes in merging galaxies
Dubinski initial particle positions for the Milky Way/Andromeda collision.
Friedli
Shlosman
MPA Numerical Cosmology Data Archive (July 2000)

Plummer (1911) : Several tables (mass, position, velocity) of plummer systems with nbody= 128, 1024, 8096, 65536 particles. All tables were generated in NEMO with mkplummer(1NEMO) as follows:
```
    mkplummer - $nbody seed=123 | snapprint - n,x,y,z,vx,vy,vz | gzip -c > tab$nbody.gz
```
and can be read back into NEMO as follows:
```
    gunzip -dc tab$nbody.gz | tabtos - p$nbody.snap "" mass,pos,vel nbody=$nbody
```
for further visualization.
xxx M.C. Plummer, MNRAS, 71, 460 (1911) and xxx S.J. Aarseth, M. Henon and R. Wielen, Astron. and Astrophys. 37, 183 (1974).
Lecar 1968 : This table (in "atos" format) lists the positions of all 25 particles. The 25th particle is the one that sets the center of mass at (0,0,0), if you have very different floating point hardware, you should compute it yourself. See also: A comparison of eleven numerical integrations of the same Gravitational 25 body problem, Myron. Lecar, Bull.Astr. 3, 91. 1968 (in: Colloque sur le problem gravitationnel des N corps).
The data can be converted as follows (although snap0=$NEMODAT/iau25.dat and should already exist in your distribution), with a few checks on center of mass and energy:
```
    atos iau25.data snap0
    snapcenter snap0 - one=t | tsf - maxprec=t
    hackcode1 snap0 snap1 eps=0 tol=0 tstop=0
    tsf snap1 maxprec=t 
```
Lookout for an upcoming updated repeat of this experiment during the 1997 IAU GA in Kyoto. This time organized by Douglas Heggie
Sellwood 1993 : The file stars.dat.gz contains the six phase space coordinates of particles at the last moment of the run described in his paper titled "A bar model for the Galactic bulge" the proceedings of the "Back to the Galaxy" conference edited by S S Holt & F Verter (New York: AIP press) pp 133--136 (1993). The 6 coordinates for all 43802 particles are arranged in the following order (note the reversed coordinates!)
```
        z, y, x, vz, vy, vx
```
but do not always appear on the same line. The fortran statement
```
    REAL x(43802),y(43802),z(43802),vx(43802),vy(43802),vz(43802)
    DO i=1,43802
        READ (*,*) z(i), y(i), x(i), vz(i), vy(i), vx(i)
    ENDDO
```
should however read the data correctly. Within NEMO the program tabtos(1NEMO) can be used as follows to read in the data in snapshot(5NEMO) format:
```
    zcat stars.dat.gz | tabtos - stars.snap block1=pos,vel nbody=43802 options=wrap
```
for further visualization. Some more practical information can be found in the README file.
F.Governato, M.Colpi and L.Maraschi 1994 : The files k17c.snap.gz and k17hp.snap.gz contain the final merger remnants from runs k17c and k17hp as described in their paper "The fate of central black holes in merging galaxies" (MNRAS, in press) They are simple examples of an oblate rotator, partially rotation supported and a prolate system with mainly radial orbits. Models and initial conditions were generated with NEMO. The data format is the "205 format" (see also atos(1NEMO) ):
```
nbodies 
ndim
time
masses
x y z
vx vy vz
eps (and NOT the potential)
```
Dubinksi 1995 : The file dubinski.tab.gz contains a simple (free format) table of 7 columns and 81920 rows: the masses and six phase space coordinates (x,y,z,vx,vy,vz) of 81920 particles that define the initial conditions for a MW/Andromeda collision. Contact John Dubinski (dubinski@cita.utoronto.ca) for more details (see also: Dubinski, Mihos & Hernquist, 1996, ApJ, 462, 576). Its the model B collision discussed in this paper).
The data here may be slightly different than the ones in other similar archives (e.g. GC3). The 81920 particles are in the following order:
```
    16384 Gal. disk
    16384 And. disk
    8192  Gal. bulge
    8192  And. bulge
    16384 Gal. halo
    16384 And. halo
```
These initial conditions start at a point less than 1 Gyr before the collision since during the 3-4 Gyr or so leading up to the collision nothing much happens. So Andromeda should look bigger than it is at the moment. The simulation starts when Andromeda is only about 120 kpc away from the Galaxy instead of the current 700 kpc so it should look about 5 times bigger than it looks now.
In NEMO this table can be read into a snapshot as follows:
```
    zcat dubinski.tab.gz |\
        tabtos - m31.ini block1=m,pos,vel nbody=81920 times=0
```
If you want to run a quick simulation, you could take a subset of the particles, multiply the masses appropriately and integrate, a subset of 640 particles, (320 per galaxy: 128 disk, 64 bulge, 128 halo):
```
    zcat dubinski.tab.gz |\
        tabtos - - block1=m,pos,vel nbody=81920 times=0 |\
        snapcopy - - select=i%128 |\
        snapscale - m31_small.ini mscale=128
    hackcode1 m31_small.ini m31_small.dat tstop=80 freqout=1 > m31_small.log
```
Friedli : (in preparation)
Shlosman : (in preparation)

Last updated on 6-jan-96 by PJT.

teuben@astro.umd.edu