APOD Robot wrote:
At least seven galaxies in the chain appear to move coherently, although others appear to be superposed by chance.
Quite interesting. Here you can see two labeled versions of the chain. (Unfortunately they are differently labeled, but Michael A. Stecker is right to call one of the galaxies NGC 4461.)
The structure of the eight-galaxy Markarian chain is investigated. A structural model with the order of distances 1b-3-4-5 is shown to have a higher probability than either of the two models studied by Meurers (1977). Analysis of the distance-velocity relationships of the galaxies using the optical-configuration regression line as the frame of reference for the radial velocities reveals that seven of the galaxies form a rigid chain system with equal angular velocity. Its right side (4406) is moving toward the earth at 1100 km/s, while the chain as a whole moves away from the earth at 700 km/s. The galaxy 4374 is found not to fit into this pattern, although it may follow the chain on its own special trajectory, perhaps a retrograde loop of Stroemgren class c.
Okay. Let's translate. Seven of the galaxies form a rigid chain system. The chain starts on the right side with galaxy NGC 4406. 4406 is the NGC number of giant elliptical galaxy M86. M86 is the huge elongated elliptical that you can see more or less in the middle of Michael A. Stecker's picture.
Apparently the galaxies that "follow M86 to the right", NGC 4438 and 4435, NGC 4461 and 4458, probably, NGC 4473 and NGC 4477, form a rigid chain. Amazing! But M86 moves towards us at 1100 km/s, while the average motion of the chain as a whole moves away from the Earth at 700 km/s. Amazing!
What about the other huge elliptical galaxy in Michael A Stecker's picture, M84? According to the Harvard abstract, M84 (whose NGC number is 4374) doesn't belong to the chain, or at least, it doesn't follow the chain on the same trajectory as the other seven galaxies.
Wowzers! This is fascinating, if you ask me!