L. J. King

Constraints on cosmological parameters from the analysis of the Cosmic Lens All Sky Survey radio-selected gravitational lens statistics

We derive constraints on cosmological parameters and the properties of the lensing galaxies from gravitational lens statistics based on the final Cosmic Lens All Sky Survey data. For a flat universe with a classical cosmological constant, we find that the present matter fraction of the critical density is Omega(m)=0.31(+0.27)(-0.14) (68%)+0.12-0.10 (syst). For a flat universe with a constant equation of state for dark energy w=p(x)(pressure)/rho(x)(energy density), we find w<-0.55(+0.18)(-0.11) (68%).Submitted to: Mon. Not. R. Astron. Soc. Abstract: A new two-image gravitational lens system has been discovered as a result of the Cosmic Lens All-Sky Survey (CLASS). Radio observations with the VLA, MERLIN and the VLBA at increasingly higher resolutions all show two components with a flux density ratio of ~7:1 and a separation of 1.34. Both components are compact and have the same spectral index. Followup observations made with the VLA at 8.4 GHz show evidence of a feature to the south-east of the brighter component and a corresponding extension of the weaker component to the north-west. Optical observations with the WHT show ~1.7 extended emission aligned in approximately the same direction as the separation between the radio components with an R-band magnitude of 21.8 +/- 0.4.

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 new gravitational lens system B1030+074

We report the discovery of a new double image gravitational lens system B1030+074 which was found during the Jodrell Bank VLA Astrometric Survey (JVAS). We have collected extensive radio data on the system using the VLA, MERLIN, the EVN and the VLBA and optical observations using WFPC2 on the HST. The lensed images are separated by 1.56 arcseconds and their flux density ratio at centimetric wavelengths is approximately 14:1 although the ratio is slightly frequency dependent and the images appear to be time variable. The HST pictures show both the lensed images and the lensing galaxy close to the weaker image. The lensing galaxy has substructure which could be a spiral arm or an interacting galaxy.

0218+357: The smallest separation lensed system

A MERLIN map with 50 mas resolution at 5 GHz together with VLA maps at other frequencies show that 0218+357 is a gravitationally lensed system with two unresolved images of a compact core separated by 335 mas, plus an Einstein ring of similar diameter. The separation is smaller by a factor > 3 than any previously reported.

Observations and Predictions of the Ratio of 3-Image to 5-Image Systems in JVAS

In JVAS we find more 5-image systems than 3-image systems. On conventional assumptions, we predict the ratio to be ∽5:1.

Cosmological Parameters from the CERES Project

As part of the CERES project we have examined ~7500 flat-spectrum radio sources from the CLASS survey. Our aims are three-fold: to determine lambda0 and Omega0 from `conventional lensing statistics, to constrain models of structure formation such as `standard CDM by comparing the observed and predicted numbers of wide-separation lenses and to determine H0 by measuring the time delay in individual lens systems. Our sample is very uniform and selection effects are understood. We also emphasise the necessity and explore the possibility of using lensing statistics to constrain lambda0 and Omega0 simultaneously. Preliminary results from the frequency of wide-separation lenses support the many other arguments against standard CDM as a viable model of structure formation. The time delay measurements of the system 0218+357 favour a Hubble constant of ~60, which is consistent with determinations from other lens systems and conventional determinations of H0. Further convergence of the H0 values from different lens systems will demonstrate both the viability of this technique as well as offer possibly the best value for the Hubble constant. A full analysis of galaxy lensing in the sample should provide the best determination of the cosmological constant to date.