## Clusters and groups of galaxies in the 2dF galaxy redshift survey. A new Catalogue

E. Tago, J. Einasto, E. Saar, M. Einasto, I. Suhhonenko, M. Jõeveer, J. Vennik, P. Heinämäki and D. L. Tucker

We create a new catalogue of groups and clusters, applying the friends-of-friends method to the 2dF GRS final release. We investigate various selection effects due to the use of a magnitude limited sample. For this purpose we follow the changes in group sizes and mean {\bf galaxy number densities within groups} when shifting nearby observed groups to larger distances. We study the distribution of sizes of dark matter haloes in $N$-body simulations and compare properties of these haloes and the 2dF groups. We show that at large distances from the observer luminous and intrinsically greater groups dominate, but in these groups only very bright members are seen, which form compact cores of the groups. These two effects almost cancel each other, so that the mean properties of groups do not change considerably with distance. Our final sample contains 10750 groups in the Northern part, and 14465 groups in the Southern part of the 2dF survey with membership $N_g \geq$ 2. We estimate the total luminosities of our groups, correcting for group members fainter than the observational limit of the survey. The cluster catalogue is available at our web-site (http://www.aai.ee/~maret/2dfgr.html).

A paper on the 2dF GRS groups with high resolution figures, and with group and galaxy tables can be found here

Here we show the spatial distribution of our groups:

The sizes of spheres are proportional to their virial radii. Only groups with at least 4 member galaxies are shown. Colors are coded according to the total luminosities of groups. Lumonosity limits: (in units of solar luminosities):

red > L=0.1E+12

yellow > L=0.2E+11

blue > L=0.5E+10

gray < L=0.5E+10

We present a catalogue of 2dF groups.

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Maret Einasto (maret@aai.ee)