New views through the gravitational telescope

New improvements in extragalactic research have recently increased the number of sources at high redshift, i.e., QSOs and especially galaxies. Gravitational lensing/magnification events are more common among them, particularly because gravitationally magnified sources are preferentially selected in the flux-limited catalogues used to find distant sources. They offer a means of investigating the matter distribution from small scales (microlensing) to large scales (macrolensing). Recent observations and realistic mass distribution models of the arc-like structures (in A370 and CI 2244-02) allow us to describe the observations well and to set new and independent conditions on the material content of the deflecting clusters; they also allow detailed studies of sources which are at the ends of the gravitational telescopes.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.