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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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