[KarlInOhio]

If the Milky Way does possess a similarly huge halo, the two galaxies’ halos may be nearly touching already and quiescently merging long before the two massive galaxies collide.

Quiescent merging? Is that what the kids are calling it today?

More seriously, does this account for the missing matter which caused galactic spin rate to not match their observed mass and eliminate the need for some type of "dark matter" which can only interact with other matter gravitationally.

[BenLurkin]

Quiescent merging?

Is the start of the process. The end is “conscious decoupling” Just ask Gwyneth Paltrow.