NAM logo, by David Le Conte

Searching for lensing by groups and clusters of galaxies

Paul M. Phillips, (NRAL)

The JVAS and CLASS searches for gravitational lens systems with image separations between 0.3 and 6 arcsec hope to reveal more than 20 new gravitational lens systems from a parent population of >10000 flat spectrum radio sources. We have recently reanalysed this data and have selected 17 candidate lens systems with image separations in the range 6 to 15 arcsec. These candidates are in the process of being followed up with multi-frequency VLA observations. Whilst providing constraints on the prevalence of mass structures associated with groups and small clusters of galaxies, this search also covers the contentious angular scales involved in the `dark lens'/binary quasar debate.

The ARCS project uses a parent sample selected from the FIRST survey to look for lensing events on scales between 15 and 60 arcsec, which are associated with cluster-sized masses. The sample was defined from extended radio sources to eliminate questions of variability hampering multiple image identification. A second stage of selection using stellar optical counterparts from the APM catalogue provides a sample with high mean redshift to increase lensing probability. The final parent sample of approximately 1500 sources has yielded no lens systems. A detailed analysis of the result is currently underway.

Maintained by Ian Howarth