  Filaments of galaxies are known to stretch between galaxy clusters at all
redshifts in a complex manner. In this Letter, we present an analysis of the
frequency and distribution of inter-cluster galaxy filaments selected from the
2dF Galaxy Redshift Survey. Out of 805 cluster-cluster pairs, we find at least
40 per cent have bone-fide filaments. We introduce a filament classification
scheme and cast the filaments into several types according to their visual
morphology: straight (lying on the cluster-cluster axis; 37 per cent), warped
or curved (lying off the cluster-cluster axis; 33 per cent), sheets (planar
configurations of galaxies; 3 per cent), uniform (1 per cent) and irregular (26
per cent). We find that straight filaments are more likely to reside between
close cluster pairs and they become more curved with increasing cluster
separation. This curving is toward a larger mass concentration in general. We
also show that the more massive a cluster is, the more likely it is to have a
larger number of filaments. Our results are found to be consistent with a
Lambda cold dark matter cosmology.
