Where does the light of giant ellipticals stop, and intra-cluster light begin?

• by JeanTate

  In many (most?) rich clusters of galaxies, there's one which looks considerably bigger and brighter than the rest*, especially if the cluster has a concentrated core. They are always giant ellipticals, and historically were called cD galaxies (and may still be so called, for all I know).

  In some rich clusters, the centers have ICL, intra-cluster light ... a diffuse, faint haze encompassing much of the core and its galaxies. Sometimes this ICL has structure, visible in very deep images; tidal tails, etc.

  In RGZ, I recently came across what looks like a really good example, centered on z_sp 0.255 SDSS J121922.75+085814.5 (see this RGZ Talk thread):

  

  How common is this? How do you tell where the cD galaxy ends and the ICL begins?

  I vaguely remember coming across similar examples, back when I was classifying SDSS GZ images (unfortunately I didn't collect them 😦); does anyone reading this have a collection of these (or similar) objects?

  *by definition there is always just one 'biggest' or 'brightest' cluster galaxy (shorthand BCG) - ties never happen - what I'm talking about is domination; #2 is considerably wimpier than #1

  Posted September 23, 2014 3:10 PM