Lenses of small angular scales from Jodrell Bank survey

Abstract

The Jodrell Bank 5 GHz sky survey provides a complete flux-limited sample of radio sources at latitude greater than 2.5 deg which are brighter than 200 mJy and have a spectrum flatter than 0.5. From the analysis of nearly 100 sources from this survey, three cases of multiply imaged lens systems have been detected, all of which have scales in the range of 0.3 to 1.3 arcseconds. The most extensively studied object among these, B0218+357, consists of the fainter source, probably lensed by a spiral galaxy of redshift 0.68. The lens models indicate that the radio ring is likely to be multiple images of two or three extended blobs forming in Einstein ring. Another system, B1422+231 is probably a quintuply imaged point source at a redshift of 3.62. Two bright images of almost equal intensity and the third image of half their intensity are indicative of the source being located near a naked cusp of the lens. The third candidate, 1938 + 666 is very faint but has extended arc-like features. The lens configurations deduced from this complete flux-limited sample indicate one of the following scenario: (1) The number density of compact but faint galaxies with mass distribution having high quadruple moment increase rapidly at high redshift. (2) The number density of compact flat spectrum sources probably decreases rapidly at redshift greater than around 3. These conclusions are necessarily preliminary in the absence of measurement of the redshift of lens galaxies