Star formation in galaxies along the Pisces-Cetus Supercluster filaments

Abstract

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

Flaming, bright galaxies along the filaments of A 2744

“…Balogh et al 1999;Lewis et al 2002;Gómez et al 2003;Finn et al 2005). It is also consistent with the result that the relative fraction of blue galaxies peaks between 1 and 2 R Vir in the nearby Shapley and Pisces-Cetus superclusters (Haines et al 2006;Porter & Raychaudhury 2006).…”

Mass, light and colour of the cosmic web in the supercluster SCL2243-0935 (z = 0.447)

“…The latter is then subdued quickly with increasing proximity to denser clusters and filaments. Therefore we expect to find an increasing fraction of passive redder galaxies with colours similar to those of early-type galaxies in regions with enhanced mass density (see Gerken et al 2004;Porter & Raychaudhury 2007;Tanaka et al 2007;Porter et al 2008;Verdugo et al 2008, for further details and observational evidence). Consequently, by selecting galaxies with early-type colours we should be able to not only identify the main clusters in SCL2243, but also to map the connecting skeleton over large distances.…”

“…Star formation is already enhanced in filaments, triggered by the increased number of interactions with neighbouring galaxies. The consumption of gas and ram-pressure stripping quickly turn blue galaxies into passive systems with colours similar to those of red sequence galaxies (see Quilis et al 2000;Gerken et al 2004;Porter & Raychaudhury 2007;Tanaka et al 2007;Porter et al 2008;Verdugo et al 2008, and references therein), whereas morphological changes happen on significantly longer time scales (Parry et al 2009;Scannapieco et al 2009). …”

H i observations of galaxies in the southern filament of the Virgo Cluster with the Square Kilometre Array Pathfinder KAT-7 and the Westerbork Synthesis Radio Telescope

“…Porter & Raychaudhury 2007;Mahajan, Raychaudhury & Pimbblet 2012). Furthermore, the hot X-ray distribution in the Virgo Cluster (see Fig.…”