Color gives any clue?

• by AGF25

  Does the color in these two galaxies give a clue to the fact that they are not actually found in their vicinity but at great distances?

  Posted July 19, 2013 9:11 AM

• by ElisabethB moderator

  The only way to determine visually if the galaxies are close together is to see if they are distorted.

  Posted July 19, 2013 10:23 AM

• by Spacer_fielding

  Can't the redshift (z values) be examined to determine if they are proximal or just superimposed?

  Posted July 21, 2013 12:50 AM

• by JeanTate in response to Spacer fielding's comment.

  Yes, but only to a certain extent (and only if both have spectroscopically determined redshifts).

  In this case, both have such, and they're very close (z=0.134). However, because redshifts - of galaxies - have both a cosmological ('according to the Hubble relationship') and a line-of-sight speed ('Doppler', a.k.a. 'peculiar velocity') one, this 'same z' means that it's only more likely that they're close to each other (in 3D space).

  How far apart can two galaxies, close together on the sky, but with 'the same' redshift be? If they're both in a massive cluster (of galaxies), easily ~10 Mpc (megaparsecs)!

  Posted July 21, 2013 8:38 AM