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M31 Relative Velocity

Attached are the relative velocities of many individual objects in the M31 galaxy in Andromeda.

One side of M31 is red shifted so it is assumed to be receding.
The other side is blue shifted so it is assumed to be approaching.
The combination indicates the disk is rotating.
I see an apparent uniformity in the distribution. Initially that might be expected.
However I assumed each object would reflect its own motion as well as the galaxy it is moving with, as one piece in the package of a trillion.
Therefore I assumed there would be slightly more red shift and less blue shift if the M31 were receding. If M31 were approaching I would expect to see the opposite.

Because there is an apparent uniformity around zero velocity then my conclusion is M31 is not moving in the direction of the Milky Way. This data does not provide lateral motion data.
I cannot find the actual individual velocities so a better analysis to verify actual uniformity is not possible.

Based on just this coarse visual presentation one could conclude the relative velocity of M31 is probably small.

Is this conclusion, M31 has little measured motion in the direction of the Milky Way, justified?

This should not be a complete surprise if the two large spiral galaxies in the local group are actually moving together. There is no real reason why they cannot. Both the Milky Way and M31 have their own troop of satellite galaxies.


I cannot find online this type of red shift / blue shift data for the rotation of objects in the M33 galaxy.
The only M33 rotation curve I found had only positive numbers so I don't know if they were absolute values or some other manipulation was done.

I do not know if anyone thought to use this method to look for M31 motion.

As I pointed out in my post on 4/12, NASA uses Calcium absorption lines to determine the velocity of M31. With that number firmly accepted perhaps no one has bothered to confirm it with an alternate method.
Would this method work?

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