The construction of a catalogue of galaxy groups from the 2-degree Field Galaxy Redshift Survey (2dFGRS) is described. Groups are identified by means of a friends-offriends percolation algorithm which has been thoroughly tested on mock versions of the 2dFGRS generated from cosmological N-body simulations. The tests suggest that the algorithm groups all galaxies that it should be grouping, with an additional 40 per cent of interlopers. About 55 per cent of the ∼ 190 000 galaxies considered are placed into groups containing at least two members of which ∼ 29 000 are found. Of these, ∼ 7000 contain at least four galaxies, and these groups have a median redshift of 0.11 and a median velocity dispersion of 260 km s −1 . This 2dFGRS Percolation-Inferred Galaxy Group (2PIGG) catalogue represents the largest available homogeneous sample of galaxy groups. It is publicly available on the WWW.

We have performed a spectroscopic study of globular clusters (GCs) in the nearest giant elliptical NGC 5128 using the 2dF facility at the Anglo-Australian Telescope. We obtained integrated optical spectra for a total of 254 GCs, 79 of which are newly confirmed on the basis of their radial velocities and spectra. In addition, we obtained an integrated spectrum of the galaxy starlight along the southern major axis. We derive an empirical metallicity distribution function (MDF) for 207 GCs (∼14 per cent of the estimated total GC system) based upon Milky Way GCs. This MDF is multimodal at high statistical significance with peaks at [Z/H] ∼ −1.3 and −0.5. A comparison between the GC MDF and that of the stellar halo at 20 kpc (∼4R e ) reveals close coincidence at the metal-rich ends of the distributions. However, an inner 8-kpc stellar MDF shows a clear excess of metal-rich stars when compared to the GCs. We compare a higher signal-to-noise ratio (S/N) subsample (147 GCs) with two stellar population models which include non-solar abundance ratio corrections. The vast majority of our sample (∼90 per cent) appears old, with ages similar to the Milky Way GC system. There is evidence for a population of intermediate-age (∼4-8 Gyr) GCs ( 15 per cent of the sample) which are on average more metal-rich than the old GCs. We also identify at least one younger cluster (∼1-2 Gyr) in the central regions of the galaxy. Our observations are consistent with a picture where NGC 5128 has undergone at least two mergers and/or interactions involving star formation and limited GC formation since z = 1, however the effect of non-canonical hot stellar populations on the integrated spectra of GCs remains an outstanding uncertainty in our GC age estimates.

We have calculated the two-point correlation functions in redshift space, xi(sigma,pi), for galaxies of different spectral types in the 2dF Galaxy Redshift Survey. Using these correlation functions we are able to estimate values of the linear redshift-space distortion parameter, beta = Omega_m^0.6/b, the pairwise velocity dispersion, a, and the real-space correlation function, xi(r), for galaxies with both relatively low star-formation rates (for which the present rate of star formation is less than 10% of its past averaged value) and galaxies with higher current star-formation activity. At small separations, the real-space clustering of passive galaxies is very much stronger than that of the more actively star-forming galaxies; the correlation-function slopes are respectively 1.93 and 1.50, and the relative bias between the two classes is a declining function of radius. On scales larger than 10 h^-1 Mpc there is evidence that the relative bias tends to a constant, b(passive)/b(active) ~ 1. This result is consistent with the similar degrees of redshift-space distortions seen in the correlation functions of the two classes -- the contours of xi(sigma,pi) require beta(active)=0.49+/-0.13, and beta(passive)=0.48+/-0.14. The pairwise velocity dispersion is highly correlated with beta. However, despite this a significant difference is seen between the two classes. Over the range 8-20 h^-1 Mpc, the pairwise velocity dispersion has mean values 416+/-76 km/s and 612+/-92 km/s for the active and passive galaxy samples respectively. This is consistent with the expectation from morphological segregation, in which passively evolving galaxies preferentially inhabit the cores of high-mass virialised regions.Comment: 10 pages, 7 figures. Submitted to MNRA

Intracluster stellar populations are a natural result of tidal interactions in galaxy clusters. Measuring these populations is difficult, but important for understanding the assembly of the most massive galaxies. The Coma cluster of galaxies is one of the nearest truly massive galaxy clusters, and is host to a correspondingly large system of globular clusters (GCs). We use imaging from the HST/ACS Coma Cluster Survey to present the first definitive detection of a large population of intracluster GCs (IGCs) that fills the Coma cluster core and is not associated with individual galaxies. The GC surface density profile around the central massive elliptical galaxy, NGC 4874, is dominated at large radii by a population of IGCs that extend to the limit of our data (R < 520 kpc). We estimate that there are 47000 ± 1600 (random) +4000 −5000 (systematic) IGCs out to this radius, and that they make up ∼ 70% of the central GC system, making this the largest GC system in the nearby Universe. Even including the GC systems of other cluster galaxies, the IGCs still make up ∼ 30-45% of the GCs in the cluster core. Observational limits from previous studies of the intracluster light (ICL) suggest that the IGC population has a high specific frequency. If the IGC population has a specific frequency similar to high-S N dwarf galaxies, then the ICL has a mean surface brightness of µ V ≈ 27 mag arcsec −2 and a total stellar mass of roughly 10 12 M ⊙ within the cluster core. The ICL makes up approximately half of the stellar luminosity and one-third of the stellar mass of the central (NGC4874+ICL) system. The color distribution of the IGC population is bimodal, with blue, metal-poor GCs outnumbering red, metal-rich GCs by a ratio of 4:1. The inner GCs associated with NGC 4874 also have a bimodal distribution in color, but with a redder metal-poor population. The fraction of red IGCs (20%), and the red color of those GCs, implies that IGCs can originate from the halos of relatively massive, L * galaxies, and not solely from the disruption of dwarf galaxies.

We measure moments of the galaxy count probability distribution function in the Two‐degree Field Galaxy Redshift Survey (2dFGRS). The survey is divided into volume‐limited subsamples in order to examine the dependence of the higher‐order clustering on galaxy luminosity. We demonstrate the hierarchical scaling of the averaged p‐point galaxy correlation functions, , up to p= 6. The hierarchical amplitudes, , are approximately independent of the cell radius used to smooth the galaxy distribution on small to medium scales. On larger scales we find that the higher‐order moments can be strongly affected by the presence of rare, massive superstructures in the galaxy distribution. The skewness S3 has a weak dependence on luminosity, approximated by a linear dependence on log luminosity. We discuss the implications of our results for simple models of linear and non‐linear bias that relate the galaxy distribution to the underlying mass.