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 with a steep faint-end slope ( \alpha =–1.26 \pm 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 : dIrrs with B - R < 1.4 ; dEs with 1.4 \leq B - R \leq 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 \pm 0.16 ) .
However , the removal of the contribution of the dIrrs from the counts produces a flat LF ( \alpha =–0.91 \pm 0.16 ) .
The dEs and the dIrrs have similar spatial distributions within the cluster except that the dIrrs appear to be totally absent within a central projected radius of about 0.2 Mpc ( H _ { o } =75 km s ^ { -1 } Mpc ^ { -1 } ) .
The number densities of both dEs and dIrrs appear to fall off beyond a projected radius of \simeq 0.35 Mpc .
We suggest that the dE and dIrr populations of A868 have been associated with the cluster for similar timescales but that evolutionary processes such as ‘ galaxy harassment ’ tend to fade the dIrr galaxies while having much less 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 .