How to find a group of galaxies. A new 2dF GRS group catalogue

1. How to find a group of galaxies.A new 2dF GRS group catalogue Erik Tago,Jaan Einasto, Enn Saar, Maret Einasto, Ivan Suhhonenko, Mihkel Jõeveer, Jaan Vennik,Pekka Heinämäki, Douglas Tucker Tartu Observatory, Tuorla Observatory, Fermilab Tartu-Tuorla seminar June 20-21 2005 Tõravere

2. Intro: why to search for groups and clusters of galaxies • To solve the principle problems of cosmology • Spatial distribution of galaxy systems : one of the main observational methods to determine cosmological parametres • Spergel test in Princeton : grow rate of rich clusters in the Universe as a solution between Dark Energy and Superstring cosmologies • CDM models were tested by the abundance of rich clusters • Obtain spatial distribution instead of redshift space - depression of God fingers • To find the density field , large scale structure, dark matter, galaxy formation and evolution etc etc Galaxy cluster is an astrophysical laboratory

3. How to find groups of galaxies 1) Differences between GROUPS and CLUSTERS of galaxies , in particular from the view of search methods 2) GROUPFINDERS : group findingmethods (short review of my earlier report ) 3) Our method : a modified cluster analysis alias friends-of-friends method (FoF) plus Dark Matter Halo test . 4) Majority of attention to group finders

4. GROUPFINDER METHODS • Minimal spanning tree • Cell count • Cluster analysis, FoF method, percolation • Minimal spanning tree • Matched filter method • Adaptive filter method • Kernel based methods • Voronoi tesselation • Wavelet transform • Maximum brightest cluster galaxies • etc

5. Observational data used 1) two degree field galaxy redshift survey (2dF GRS) final release 2004, N=245000 gal., our sample N=184000 2) Sloan DSS Data Release 3 N=550000 gal., our sampleN=350000

6. The APM Galaxy Survey ( 1/10 th of the sky)

7. APM and 2dFGRS sky coveridge

8. 2dF GRS slices in wedge diagram

9. 2dF GRS redshift distribution

10. The 2dF GRS samples used and the FoF parameters --------------------------------------------------------------------------------------- Sample Cat RA DEC Ngal Ngroups Nsingle DV0 DR0 L0 a km/s Mpc/h --------------------------------------------------------------------------------------- 2dF GRS N A 147.5...223 -7...+3 78067 9553 48861 750 0.3 2dF GRS S A 325...55 -37.5...-23 106328 12414 69299 750 0.3 2dF GRS N B 147.5...223 -7...+3 78067 10750 44134 200 0.25 414 1.46 2dF GRS S B 325...55 -37.5...-23 106328 14465 61344 200 0.25 414 1.46 Table 1

11. Total group luminosity vs distance

12. Problems • Flux limited sample involve selection effects depending on distance • Density-luminosity effect • Volume effect – distant clusters are larger • Evolutionary effect • Merging of subgroups

13. Our groupfinder: description of steps 1) FoF with CONSTANT search radius alias linking length (LL) alias neighbourhood radius 2) preliminary FoF with variable LL; scaling law for LL obtained from previous step 3) increasing shift of observed clusters to larger distances (about 80 clusters,proposed by E. Saar) to determine scaling law for LL, starting scaling law from earlier step a) from cluster density LL ~(Rho)^1/3 b) direct determination of LL changing law applying minimal spanning tree method to find LL

14. The main result of our method • Selection effect involved by flux limited sample AND • Density-lumiosity relation CANCEL each other out and in resulting scaling law LL slightly increase with distance (2 times for our groups instead of 7 times for Eke etal groups from z=0 to z=0.2) Important for group selection dependence on distance is not the mean spatial density but intrinsic density of groups

15. LL scaling law :

16. Results 7) Final FoF procedure with scaling: ARCTAN law LL/LLo = 1+a*ATAN(D/L) D is distance, L and a are parametres found 8) Results : Fig. 14, Tab 1 and 3 9) Comparison to other catalogues, advances of our catalogue a) intermediate version between Eke etal and Yang etal b) independent of models c) Eke etal distant groups are too large, nearby groups too small in comparison to our groups (includes filaments of superclusters) 10) Catalogue of GROUPS, GALAXIES of GROUPS and ISOLATED GALAXIES in the North and South galactic hemisphere (6 tables at all).

17. Group catalogues based on the 2dF GRS Sample Ngal Ngr(n >= 2) Ngr(n >= 4) zlim mlim method % in gr, -------------------------------------------------------------------------------------- Merchan 60000 2209 0.25 19.45 FoF mod 2002 Eke 191440 28877 7020 0.11 (med) FoF +mock 55 2004 Yang * 151280 12096 2502 0.01-0.2 19.45 FoF+mock 25 2004 Tago * 184395 25215 4852 0.009-0.2 FoF mod+DMH 43 2004/05 --------------------------------------------------------------------------------------- * revised catalogue in comparison to the published in preprint Table 3

18. Intrinsic median density of groups vs distance

19. FoF result for 2dF GRS at A933 cluster

20. FoF result at A1620 cluster

21. Distribution of the 2dF GRS group distance: northern and southern areas

22. 2dF group spatial density vs distance

23. The 2dF GRS group catalogue ------------------------------------------------------------------------------------------------------------------- # id Ngal RA DEC dist s_sky disp_v Rvir Lmain Lobs Ltot Mpc Mpc km/s Mpc L_sun -------------------------------------------------------------------------------------------------------------------- 1 4 153.10069275 -3.51675248 229.78 0.6809 147.22 0.2472 0.602020E+10 0.151832E+11 0.194104E+11 2 10 153.12361145 -3.71129107 176.59 0.8914 329.80 0.3551 0.290560E+11 0.762542E+11 0.893009E+11 3 24 153.23248291 -2.66546297 131.60 0.9479 346.43 0.2673 0.239150E+11 0.112659E+12 0.123242E+12