Star formation in galaxies falling into clusters along supercluster-scale filaments

TL;DR

This study reveals that galaxies falling into clusters along supercluster filaments experience a sudden star formation burst before reaching the virial radius, mainly due to galaxy interactions prior to gas stripping by the intracluster medium.

Contribution

It provides observational evidence of a star formation enhancement in infalling galaxies along filaments, highlighting the role of galaxy interactions before gas removal in clusters.

Findings

Star formation peaks 2-3 Mpc from cluster centers.

Fainter dwarf galaxies show the most significant burst.

Galaxy interactions before gas stripping drive the star formation increase.

Abstract

With the help of a statistical parameter derived from optical spectra, we show that the current star formation rate of a galaxy, falling into a cluster along a supercluster filament, is likely to undergo a sudden enhancement before the galaxy reaches the virial radius of the cluster. From a sample of 52 supercluster-scale filaments of galaxies joining a pair of rich clusters of galaxies within the two-degree Field Redshift Survey region, we find a significant enhancement of star formation, within a narrow range between 2-3 h/70 Mpc of the centre of the cluster into which the galaxy is falling. This burst of star formation is almost exclusively seen in the fainter dwarf galaxies (M_B> -20). The relative position of the peak does not depend on whether the galaxy is a member of a group or not, but non-group galaxies have on average a higher rate of star formation immediately before falling into a cluster. From the various trends, we conclude that the predominant process responsible for this rapid burst is the close interaction with other galaxies falling into the cluster along the same filament, if the interaction occurs before the gas reservoir of the galaxy gets stripped off due to the interaction with the intracluster medium.