Astronomy Question concerning redshift?

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Jared

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A spiral galaxy will have a red and blue shift sides on 1 side or the other.

the arms in a spiral galaxy rotate in 1 direction based on random chance, but which ever direction the arms are rotating, as an arm is rotating or moving away from the observer, the wavelengths in the light are stretched and a red shift occurs on whichever side of the galaxy that arm is located in.

the center mass is a supermassive black hole that propels the galaxy into a spiral, thus forming the arms and their red and blue shifts.

basically the arm in the galaxy that is moving AWAY from you will have stretched light wavelengths and the result is a slight redshift.
 
How might you determine what part of a galaxy's redshift is caused by the galaxy's orbital motion about the center of mass of its cluster?
 
Rotation will cause spectral lines to smear, because part of the galaxy is rotating toward you, and part is rotating away. So the parts that are moving toward you will be blueshifted in relation to the center, and the parts that are moving away will be redshifted in relation to the center.

The technique to eliminate this is to average the smear to find its center, and then use that value as the basis for determining the redshift of the galaxy as a whole.

EDIT: Oops, I misunderstood your question, but the answer is similar.

In order to determine what the orbital motion of the galaxy around the center of mass of its galactic cluster contributes to the red-shift, you would measure the redshifts of all of the galaxies in the cluster, and average those to determine the redshift of the cluster as a whole, and then compare it to the redshift of the target galaxy.

Sorry about the wrong answer there.
 
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