Extremely Large Telescope

Abstract:

We present deep wide-field Ks-band observations of six Hyperluminous Infrared Galaxies (HLIRGs) spanning a redshift range 0.44 < z < 1.55. The sample resides in a wide variety of environments, from the field to Abell 2 clusters, with a mean galaxy-HLIRG clustering amplitude of 〈Bgh〉 = 190 ± 45 Mpc1.77. The range in environments, and the mean clustering level, are both greater than those seen in local IR-luminous galaxies, from which we infer that the range of galaxy evolution processes driving IR-luminous galaxy evolution at z > 0.5 is greater than locally, and includes mergers between gas-rich spiral galaxies in the field, but also includes encounters in clusters and hierarchical build-up. The similarity in the range of environments and mean clustering amplitude between our sample and QSOs over a similar redshift range is consistent with the interpretation where evolutionary connections between IR-luminous galaxies and QSOs are stronger at z > 0.5 than locally, and that, at these redshifts, the processes that drive QSO evolution are similar to those that drive IR-luminous galaxy evolution. From comparison of the HLIRG and QSO host galaxies we further postulate that a larger fraction of IR-luminous galaxies pass through an optical QSO stage at z > 0.5 than locally.

Abstract:

The construction of a catalogue of galaxy groups from the Two-degree Field Galaxy Red-shift Survey (2dFGRS) is described. Groups are identified by means of a friends-of-friends 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 World Wide Web.