2.5 Gyr N-body simulation of the Milky Way and Magellanic Clouds
Data files
Mar 10, 2026 version files 17.73 GB
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lsmcmodelA0000_0500Myr.zip
3.66 GB
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lsmcmodelA0520_1000Myr.zip
3.51 GB
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lsmcmodelA1020_1500Myr.zip
3.51 GB
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lsmcmodelA1520_2000Myr.zip
3.50 GB
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lsmcmodelA2020_2500Myr.zip
3.55 GB
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README.md
2.93 KB
Abstract
The Large and Small Magellanic Clouds (LMC and SMC, respectively) are the largest satellite galaxies of the Milky Way (MW). They have been interacting with each other and the MW over the past few billion years (Gyr). We modeled the interactions over 2.5 Gyr using the N-body code PKDGrav. This simulation includes the MW, LMC, and SMC and snapshots are saved every 20 million years (Myr). Each .ZIP file contains 500 Myr of snapshots. There are two close interactions between the LMC and SMC that occur at 1.26 and 2.06 Gyr into the run of the simulation. The snapshot where the location of the LMC relative to the MW is closest to observed is 2.2 Gyr into the run.
Dataset DOI: 10.5061/dryad.1vhhmgr82
Description of the data and file structure
This is a simulation of the Milky Way and Magellanic Clouds over 2.5 Gyr.
Files and variables
File: lsmcmodelA0000_0500Myr.zip
Description: Snapshot files for every 20 million years from the first 500 million years of the simulation's run. The file names end with a step number, where each step is 5 million years. Each file contains star and dark matter particles, indexed in order Milky Way - LMC - SMC. The Milky Way contains 2.5×105 dark matter particles and 2.4×105 star particles. The LMC contains 2.38×106 dark matter particles and 1.62×106 star particles. The SMC contains 2.9×105 dark matter particles and 2.25×105 star particles. Position values are in units of kpc, velocity values are in units of km s-1, mass is in units of 2.32×105 Msol, and gravitational potential (phi) is in units of 9.98×10-1 km2 s-2.
File: lsmcmodelA0520_1000Myr.zip
Description: Snapshot files for every 20 million years starting at 520 Myr and ending at 1 Gyr.
File: lsmcmodelA1020_1500Myr.zip
Description: Snapshot files for every 20 million years starting at 1.02 Gyr and ending at 1.5 Gyr.
File: lsmcmodelA1520_2000Myr.zip
Description: Snapshot files for every 20 million years starting at 1.52 Gyr and ending at 2 Gyr.
File: lsmcmodelA2020_2500Myr.zip
Description: Snapshot files for every 20 million years starting at 2.02 Gyr and ending at 2.5 Gyr.
Code/software
The individual snapshot files are in tipsy file format. We use the python package pynbody to open and analyze the simulation files. Once you install pynbody and unzip the files, you can read them using:
import pynbody as pb
sim = pb.load(filename)
You can separate out the star particles using sim.s and the dark matter particles using sim.d.
To look at stars from each galaxy, do:
mw = sim.s[:240000] # Milky Way is the first 2.4*10^5 star particles
lmc = sim.s[240000:240000+1620000] # LMC is the 1.62*10^6 star particles after the Milky Way
smc = sim.s[240000+1620000:] # SMC is all the star particles after the LMC
There are multiple keys corresponding to position or velocity. 'x', 'y', and 'z' are the x, y, and z coordinates of each particle, and 'pos' gives all three coordinates in the form [x,y,z]. The keys 'vx', 'vy', 'vz', and 'vel' work the same but with velocity components. 'r' gives the radius in spherical coordinates (distance from the point (0,0,0)) while 'rxy' gives the radius in cylindrical coordinates (distance from z-axis). If you center the simulation on a galaxy, 'vrxy' gives the radial velocity in cylindrical coordinates, and 'vcxy' gives the azimuthal velocity.