A gorgeous view of M51 - the Whirlpool Galaxy

[Bernardo de La Paz]

2. Chemical compounds. They reflect differentially in bands of spectrum including infrared.

Actually, not mainly reflection for starlight, which is emission. There is also filtering by dust clouds and that tend to be the "redder" areas. The image probably includes some infrared emissions, which are better at getting through dust and gas and those are usually assigned very red colours.

If you are thinking of "red shift", that requires much higher velocities than galactic rotation (guessing 10,000 to 100,000 mph). Red shift is for objects going away from us (receding) at speeds a significant fraction of the speed of light. 36,000 mph is 10 miles per second. One percent (faint red shift) of the speed of light is 1,860 miles per second. So galactic motion does not produce visible red shift (possibly it might be detectable by careful examination of spectral lines, I don't know).