Malcolm N. Bremer

A complete infrared Einstein ring in the gravitational lens system B1938+666

We report the discovery, using NICMOS on the Hubble Space Telescope, of an arcsec-diameter Einstein ring in the gravitational lens system B1938 + 666. The lensing galaxy is also detected, and is most likely an early-type galaxy. Modelling of the ring is presented and compared with the radio structure from MERLIN maps. We show that the Einstein ring is consistent with the gravitational lensing of an extended infrared component, centred between the two radio components.

The Westerbork Northern Sky Survey: Current Status of the Survey and the Study of Large Scale Structure

We give a short description of the Westerbork Northern Sky Survey (WENSS) as well as its current status. This is followed by a presentation of the results from our analysis of the angular two-point correlation function for WENSS, as well as for the new version of the Green Bank 6cm survey. We find that the amplitude in the angular two-point correlation function for the Green Bank surve is about a factor of 3 higher than that for WENSS. We have modelled this result and find that the difference in amplitude between the two surveys indicates that the evolution of the spatial distribution of radio sources is a function of the characteristics of the radio sources.

Gigahertz Peaked Spectrum Sources as Cosmological Probes

We have discovered that the optical to near-infrared properties of Gigahertz Peaked Spectrum (GPS) galaxies are consistent with them having old stellar populations, with little or no contamination from their active nuclei. They seem to be a homogeneous class of object, in luminosity and scatter comparable to first ranked cluster galaxies. At z ∼ 1 the K band luminosities are about a magnitude fainter than expected for passively evolving ellipticals, just as in the case of radio-quiet giant ellipticals at similar redshifts. This may be caused by the dynamical evolution of the galaxies counteracting the change in mass-to-light ratio of the systems. We have selected a new sample of faint GPS sources from the Westerbork Northern Sky Survey, which yielded a large sample of potentially high redshift GPS galaxies. We believe that this is an ideal sample to study the evolution of giant ellipticals at z > 1.

The Connection between Radio Halos and Rich Clusters: The Case of A3667 and a Search for Distant Radio Halos

Radio halos are large amorphous regions of radio emitting plasma with sizes of order 1 Mpc (throughout, H 0 = 50 km s-1 Mpc -1) located in extremely rich clusters (for reviews, see Jaffe 1992; Feretti & Giovannini 1995). These sources are rare; only 10 or so are known. Despite the fact that all of these examples were discovered more than 10 or 20 years ago, their nature is still a mystery and a number of basic questions have not yet been answered satisfactorily.