What is it that makes a galaxy rotate, is the gas it was formed from rotating?
A small tornado can make a hundred turns in a second. A huge cyclone can make only one turn in a week; otherwise it would be unstable.The interesting question is why such a rotation of the system as a whole is observed on galaxy scales but not on galaxy cluster scales.
As every thing was much closer in the distant past, i would expect if there was any rotation in the BB plasma every thing would have the same rotation, as this is not soThe matter was rotating locally when the galaxy formed, like local turbulent swirls in otherwise expanding gas. The interesting question is why such a rotation of the system as a whole is observed on galaxy scales but not on galaxy cluster scales.
The FRW metrics, describing the homogenous approximation to the Universe, are not rotating as a whole. I expect non-rotation on scales for which the Universe seems homogeneous, currently 100 Mpc. Galaxy cluster scale is way below that so I asked in another thread why clusters are not rotating with zero answers.
I doubt anyone knows, the theory of galaxy formation is in its infancy, not to mention cluster formation....rotation must occure in issolated systems, (seperate clouds of gas), i have read about the conservation of angular momentum but why would this have a prefered direction in a vast cloud of gas.