DOI: 10.5281/zenodo.8015660
title: Welcome again, Magellanic Clouds!

description: This repository contains data for the simulations of Large Magellanic Cloud (LMC)'s<br> interaction with the Milky Way (MW).<br> Some of the data and all scripts require the Agama framework for stellar dynamics.<br> Units are: length = 1 kpc, velocity = 1 km/s, time = 0.978 Gyr (for simplicity,<br> referred to as Gyr throughout the text), mass = 232500 Msun, G = 1.<br> <br> There are six simulations with different combinations of initial LMC and MW mass<br> (see Section 2 in Vasiliev 2023 for a definition of initial profiles of both galaxies):<br> <br> name M_LMC[Msun] M_MW[Msun] time[Gyr] comment<br> L2M10 2e11 10e11 11 second passage, Tperi ~ 8.8 Gyr<br> L2M11 2e11 11e11 10 --"--, Tperi ~ 6.5 Gyr<br> L3M10 3e11 10e11 11 --"--, Tperi ~ 8.2 Gyr<br> L3M11 3e11 11e11 10 --"--, Tperi ~ 6.3 Gyr<br> L2M10first 2e11 10e11 4 first passage starting from apocentre<br> L3M10rad 3e11 10e11 11 radially anisotropic MW halo (beta=0.5)<br> <br> Each simulation's folder contains the following data:<br> - potential.ini: time-dependent potential of the entire system represented by<br> two series of Multipole expansions for each galaxy (the one for the LMC is moving),<br> plus the fixed MW stellar potential, plus non-inertial acceleration of the MW-centric<br> reference frame. This potential can be used to integrate orbits (resimulation).<br> - potential_bse.ini: same, but with potentials represented by BasisSet expansions<br> (not recommended, because it is generally slower to evaluate, but this format can<br> be more readily used in other galaxy modelling packages).<br> - potential_lmc_bound.ini: time-dependent moving potential of particles still bound<br> to the Magellanic system (defined so that their total energy in this potential is<br> negative).<br> - potential_lmc_init.ini: LMC potential at the start of the simulation.<br> - potential_mw_now.ini: Milky Way potential at present time (without the non-inertial<br> acceleration term).<br> - potential_mw_init.ini: Milky Way potential at the start of the simulation.<br> - trajlmc.txt: Galactocentric trajectory of the LMC (also used in the potentials).<br> - boundmass.txt: evolution of bound mass of the LMC (in units of Msun).<br> - snapshot.npz: numpy zip archive with the following arrays:<br> * pos: Nx3 array of particle positions at present time (t=0) in the standard<br> Galactocentric coordinate system from Astropy (where the Sun is at -8.122,0,0.02);<br> * vel: Nx3 array of particle velocities;<br> * mass: array of particle masses of length N;<br> * tstrip: time at which the particle became unbound from the LMC (length Nlmc),<br> if greater than zero, it is still bound at present time.<br> The first Nlmc = 2e6 particles represent the Magellanic system, the next 7e6<br> represent the MW halo, and the remaining 1e6 represent the stellar disc+bulge;<br> all particles from the same category have identical masses.<br> <br> The folder "scripts" contains the following Python scripts or Jupyter notebooks:<br> - find_lmc_orbit.ipynb: notebook illustrating the method for finding orbital initial<br> conditions by running a bunch of simulations with slightly different initial points.<br> Instead of running an actual simulation, it creates a fake trajectory by integrating<br> equations of motion of LMC and MW as two extended rigid bodies, taking into account<br> dynamical friction (but note that this approximation is not particularly realistic).<br> One may adapt the code to actual simulations by replacing one specific routine.<br> - resimulate_orbits.py: script for performing orbit integration in the recorded<br> approximated potential of both galaxies; the actual particle trajecties in the<br> simulation may differ individually, but on average this gives a realistic result.<br> - membership_analysis.py: script for computing the probability of Magellanic<br> association for nearby dwarf galaxies, using data from the text file satellites.txt<br> (positions and distances taken from the catalogue of McConnachie,<br> https://www.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/en/community/nearby/<br> and proper motions from Battaglia et al.2022).<br> - plot_snapshot.py: script for plotting the spatial distribution and velocity map of<br> Magellanic debris, together with the observed positions and velocities of dwarfs.<br> - adaptive_histogram.py: auxiliary module for variable-bandwidth KDE construction.