Correlation Function of Galaxy Groups

We use the Updated Zwicky Catalog of galaxies (Falco et al. 1999) to generate a catalog of groups, by means of a friend-of-friend algorithm. The groups identified have 4 or more members and a surrounding density contrast, δρ/ρ = 80. They cover the region −4 < δ < 90, |b| > 20 spanning over the radial velocity range of 2000 km s < cz < 15000 km s. The total sample (hereafter GUZC) comprises 517 groups. The correlation length of the total sample is well fitted with a power law ξ(r) = (r/r0) γ with parameters r0 = 9.0± 0.4 h Mpc and γ = −1.67± 0.09 for values of r < 70 hMpc, declining to homogeneity at larger scales. Three subsamples defined by the range of group virial masses M were used to have their clustering properties examined throughout the autocorrelation function. We find an increase of the amplitude of the correlation function according to the group masses which extends the results of the r0−dc relation for galaxy systems at small dc. We obtain r0 = 9.5±0.5h Mpc (γ = −1.81±0.12), r0 = 10.8±0.7h Mpc (γ = −1.77±0.17), and r0 = 14.1±1.2h Mpc (γ = −1.65±0.22) for mass ranges 5×10M⊙ < M < 4×10 M⊙ , 2× 10M⊙ < M < 4× 10 M⊙ and 5× 10 M⊙ < M < 4× 10 M⊙ respectively. For completeness we have also analyzed a sample of groups obtained from the Southern Sky Redshift Survey (da Costa et al.1998) in the range of virial masses 5 × 10M⊙ < M < 4×10M⊙ to compare the results with those obtained from GUZC. The correlation function of this sample can be fitted with a power law with parameters r0 = 8.4 ± 1.8 hMpc and γ = −2.0± 0.7. Subject headings: cosmology: large-scale structure of universe — galaxies: clustering — galaxies: statistics Grupo de Investigación en Astronomı́a Teórica y Experimental (IATE), Observatorio Astronómico, Laprida 854, Córdoba and CONICET, Argentina. Departamento de Astromomia, Observatório Nacional, Rua General José Cristino 77, Rio de Janeiro, 20921-030, Brazil. 1