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Keywords:

  • galaxies: haloes;
  • galaxies: kinematics and dynamics;
  • Local Group;
  • Magellanic Clouds;
  • large-scale structure of Universe

ABSTRACT

Analysing all Galaxy And Mass Assembly (GAMA) galaxies within a factor of 2 (±0.3 dex) of the stellar mass of the Milky Way (MW), there is a 11.9 per cent chance that one of these galaxies will have a close companion (within a projected separation of 70 kpc and radial separation of 400 km s−1) that is at least as massive as the Large Magellanic Cloud (LMC). Two close companions at least as massive as the Small Magellanic Cloud (SMC) are rare at the 3.4 per cent level. Two full analogues to the MW–LMC–SMC system were found in GAMA (all galaxies late-type and star-forming), suggesting that such a combination of close together, late-type, star-forming galaxies is rare: only 0.4 per cent of MW mass galaxies (in the range where we could observe both the LMC and SMC) have such a system. In summary, the MW–LMC–SMC system is a 2.7σ event (when recast into Gaussian statistics).

Using cross-correlation comparisons we find that there is a preference for SMC–LMC binary pair analogues to be located within 2 Mpc of a range of different luminosity groups. There is a particular preference for such binaries to be located near Local Group luminosity systems. When these groups are subdivided into small magnitude gap and large magnitude gap subsets, the binaries prefer to be spatially associated with the small magnitude gap systems. These systems will be dynamically less evolved, but still offer the same amount of gravitational dark matter. This suggests that binaries such as the SMC–LMC might be transient systems, usually destroyed during vigorous merger events. Details of a particularly striking analogue to the MW–SMC–LMC and M31 complex are included.