First, you need to obtain the 2dFGRS data release for galaxies.

http://www.mso.anu.edu.au/2dFGRS/

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Step 1. Find the groups in 2dFGRS.

I. Selections: 

   1. 0.01 <= z <= 0.20
   2. completeness > 0.8     (redshift completeness)
      (Note there is a 0.91 completeness in the parent catalogue)   
   3. m < mmax        (b_J-band)
   4. redshift quality q >= 3

   We adopt these selections in order to have a fair sample to search the 
   groups. After these selections, we get 151280 galaxies which covers 
   an area of 1124 square degrees

   The galaxies thus selected are listed in `i2dFGRS' with format:
     1. galaxy id; 2. galaxy id in 2dFGRS

II. group catalogue: (We are using luminosity normalized to z=0.1)

   1. group members are stored in `2dFGRS_member' with format:
     1. group id; 2. galaxy id; 3. galaxy id in 2dFGRS
     (Note that not all the galaxies are linked the groups, only
      104912 galaxies are linked to groups.)

   2. group properties are stored in '2dFGRS_group' with format:
     1. group id; 
     2. halo mass in log M_{\odot}/h; (estimated using the ranking of groups)
     3. group L_{-18} log L_{\odot}/h^2; (characteristic group luminosity)
     4. z; (they are luminosity weighted group redshift)
     5. brightest galaxy id; 
     6. brightest galaxy id in 2dFGRS;

   Note that the halo mass are estimated using the ranking of the groups
   according to their L_{-18}. [Refer to Yang et al. (2005c, MNRAS, 358, 217)
   for the details of the halo mass assignment.]
 
   At high redshift, the small halos are not all resolved in our group 
   catalogue, thus suffer from the incompleteness. [Refer to Yang et al. 
   (2005b, MNRAS, 357, 608) for the incompleteness.] 

   The first 3 lines in `2dFGRS_group' contain such information:
      0  -12.8779   10.5000    0.2000        0        0
      0  -12.1381   10.0000    0.1400        0        0
      0  -11.7860    9.6000    0.0800        0        0

   Halos with log mass > 12.8779 are complete with redshift z<0.2.
   Halos with log mass [12.1381 12.8779] are complete with redshift z<0.12.
   Halos with log mass [11.7860 12.1381] are complete with redshift z<0.08.

   Those halos not complete are assigned negitive values.
   No halos are assigned mass smaller than 11.7860.


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