The nature of the dwarf population in Abell 868

P J Boyce, S Phillipps, J B Jones, S P Driver, R M Smith, W J Couch

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We present the results of a study of the morphology of the dwarf galaxy population in Abell 868, a rich, intermediate-redshift (z = 0.154) cluster which has a galaxy luminosity function (LF) with a steep faint-end slope (alpha = -1.26 +/- 0.05). A statistical background subtraction method is employed to study the B - R colour distribution of the cluster galaxies. This distribution suggests that the galaxies contributing to the faint-end of the measured cluster LF can be split into three populations: dwarf irregular galaxies (dIrrs) with B - R < 1.4; dwarf elliptical galaxies (dEs) with 1.4 <less than or equal to> B - R less than or equal to 2.5; and contaminating background giant ellipticals (gEs) with B - R > 2.5. The removal of the contribution of the background gEs from the counts only marginally lessens the faint-end slope (alpha = -1.22 +/- 0.16). However, the removal of the contribution of the dIrrs from the counts produces a flat LF (alpha = -0.91 +/- 0.16). The dEs and the dIrrs have similar spatial distributions within the cluster, except that the dh-rs appear to be totally absent within a central projected radius of about 0.2 Mpc (H-0 = 75 km s(-1) Mpc(-1)). The number densities of both dEs and dIrrs appear to fall off beyond a projected radius of similar or equal to 0.35 Mpc. We suggest that the dE and dIrr populations of A868 have been associated with the cluster for similar time-scales, but evolutionary processes such as 'galaxy harassment' tend to fade the dIrr galaxies while having a much smaller effect on the dE galaxies. The harassment would be expected to have the greatest effect on dwarfs residing in the central parts of the cluster.

Original languageEnglish
Pages (from-to)277-282
Number of pages6
JournalMonthly Notices of the Royal Astronomical Society
Publication statusPublished - 21 Nov 2001


  • methods : data analysis
  • galaxies : clusters : general
  • galaxies : clusters : individual : Abell 868
  • galaxies : dwarf
  • galaxies : evolution
  • galaxies : luminosity function, mass function


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