What the present observed lens systems tell about the lensing agent

Abstract

Limits on the mass and size of the lens can be obtained from the observed properties of the images. For point lens the system is overdetermined. However, the structure of an extended lens is not uniquely determined from the images. The present observed lenses are suggestive of large scale matter distribution at three scales: galaxies of core radius 1–3 kpc and mass 10¹¹ – 10¹² M _⊙, massive dark halos of core radius 10–30 kpc and mass 10¹³ M _⊙ and compact clusters of core radius 100 – 200 kpc. But inferences drawn from lens statistics are likely to be biased. We are likely to observe galaxies of higher ellipticity or compact clusters more often in a finite Universe using instruments having limitations. At a specific redshift of the lens, a specific class of lenses will have projected surface mass density closer to the critical value and consequently, their influence will be more pronounced.