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Table 3

Comparing major and minor merger hypotheses, where “Y” means consistency with the observations.

Observational features Major Intermediate Minor Comments
merger merger merger
3:1–5:1 5:1–12:1  >12:1

Loop shape Y? Y? Y In minor merger, the loops trace the progenitor orbit, while in a
major merger, loops are formed by particles coming back from a tidal tail
Loop size Y Y Y
Loop surface mass density Y Y Y Most models can reproduce the stellar mass surface density
Loop eccentricity Y N? N With an orbital eccentricity of 0.9–1, a merger with mass ratio  >12:1
would need more than a Hubble time to reach fusion
Visibility of Y Y N Major mergers provide a thick disc component after complete fusion of the nuclei,
remnants and low dynamic friction means the remnant nucleus should be seen in a minor merger
Gas warp Y Y N Major merger predicts a gas warp unlike a minor merger with high mass ratio
Gas & PAH emission Y Y ? N Major merger predicts residual gas and PAH emission above the disc, and
above the disc this should be explained by another mechanism in a minor merger
Colours of loops Y Y N? For a minor merger the satellite should be a relatively massive, red dwarf elliptical

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