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For the following graph, I have some confusions:

  1. How do galaxies rank by mass? We know that on main-sequence, more luminous stars are also more massive, so I guess it also applies to galaxies.

  2. Do red sequence galaxies split into blue galaxies, or do blue galaxies merge into bigger red galaxies?

  3. Can galaxies ever be born as red sequence members? I doubt it because all galaxies should start from blue. But I am not 100% sure.

  4. Do red sequence galaxies tend to become redder over time?

  5. Do large galaxies use up star forming gas more rapidly than smaller galaxies?

color-luminosity chart for galaxies

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    $\begingroup$ These are quite a few questions. I'd recommend dividing them up, and having this question focus on just one of them. $\endgroup$ – HDE 226868 Dec 11 '16 at 2:28