Superclusters and large-scale filaments of galaxies

Superclusters are the largest gravitationally bound systems in the Universe. They are dynamically unrelaxed entities, and consequently tend to be more filamentary than clusters themselves. Using statistics sensitive to filamentary structures (e.g. minimal spanning trees), Somak Raychaudhury and collaborator Suketu Bhavsar (University of Kentucky, USA), have compiled a catalogue of superclusters from an almost complete redshift survey of Abell clusters out to z=0.1 (obtained by John Huchra and collaborators). This will help us to delineate the largest bound structures in the local Universe. Further research using this survey will include:

  • The clustering statistics of superclusters, which will reveal the clustering properties of matter in the linear regime, and the nature of dark matter haloes
  • Studies of individual superclusters combining optical observations with X-ray observations from ROSAT, ASCA and XMM

abellclusters

All clusters of galaxies with redshifts z < 0.2 in the Abell catalogue of clusters. The 739 clusters with z < 0.1 are plotted in blue, and the two richest known superclusters among them are marked. There are 2052 clusters between z=0.1 and 0.2. These clusters are optically selected, and many of their redshifts are estimated from the magnitudes of their few brightest galaxies. Note that there are very few clusters in the catalogue within 30 degrees of either side of the plane of the Milky Way.

We have been searching for diffuse Mpc-long radio emission (at 320 MHz and 1.4 GHz) from VLA and GMRT observations. A previously unknown (>6/h Mpc) filament (Zw2341.1+0000) has been discovered at z=0.3, for which X-ray, radio and optical data together suggest that it is a supercluster in formation. The energetics of accretion shocks generated in forming large-scale structures (giving rise to x-ray emitting gas) are sufficient to produce enough high energy cosmic-ray electrons that is required to explain the observed radio emission, provided a magnetic field of strength B > 0.3 microGauss is present in the intercluster medium.

pisces-cetus

The Pisces-Cetus supercluster, the most prominent supercluster in the 2dFGRS survey region, consisting of 25 clusters of galaxies, defined by a minimal spanning tree analysis of our nearby clusterS sample. Each cluster, represented as red circles, is at a distance of less than 20/h Mpc from its nearest neighbour (except when shown as dashed line). The axes represent Right Ascension and Declination (Porter and Raychaudhury 2004).

Researchers: Somak Raychaudhury, Scott Porter