OAC ASTRO MEETING

ABSTRACT

I will present new results in the study of two high-z clusters of galaxies detected through the strong gravitational lensing of background sources. A cluster of galaxies at redshift about 0.7 has been predicted on the base of its perturbation on a nearby double quasar, and then clearly detected on deep infrared images. I have computed an improved model for the gravitational lens, allowing a new determination of the Hubble constant based of the measured time delay.
Then I will briefly show preliminary results about a cluster of galaxies at redhsift 0.6 deteted around the radio-galaxy: This was predicted (from ground based images) because it forms a giant gravitational arc, and only afterwards it's been detected on HST optical images. The system appears to have a very high M/L ratio compared with similar systems. These two systems are probaly among the first cases of high redshift clusters of galaxies detected on the base of their strong gravitational lens effect.
I will finally discuss the possibility to detect completely dark cluster of galaxies through gravitational lensing.