We investigate the variation of current star formation in galaxies as a
function of distance along three supercluster filaments, each joining pairs of
rich clusters, in the Pisces-Cetus supercluster, which is part of the 2dFGRS.
We find that even though there is a steady decline in the rate of star
formation, as well as in the fraction of star forming galaxies, as one
approaches the core of a cluster at an extremity of such a filament, there is
an increased activity of star formation in a narrow distance range between
3-4/h_70 Mpc, which is 1.5-2 times the virial radius of the clusters involved.
This peak in star formation is seen to be entirely due to the dwarf galaxies
(-20<M_B<-17.5). The position of the peak does not seem to depend on the
velocity dispersion of the nearest cluster, undermining the importance of the
gravitational effect of the clusters involved. We find that this enhancement in
star formation occurs at the same place for galaxies which belong to groups
within these filaments, while group members elsewhere in the 2dFGRS do not show
this effect. We conclude that the most likely mechanism for this enhanced star
formation is galaxy-galaxy harassment, in the crowded infall region of rich
clusters at the extremities of filaments, which induces a burst of star
formation in galaxies, before they have been stripped of their gas in the
denser cores of clusters. The effects of strangulation in the cores of
clusters, as well as excess star formation in the infall regions along the
filaments, are more pronounced in dwarfs since they more vulnerable to the
effects of strangulation and harassment than giant galaxies.Comment: 10 pages, 9 figures; accepted for publication in MNRA
