CLASS Survey Gravitational Lenses

Minimum credit line: Image courtesy of NRAO/AUI and the CLASS collaboration(for details, see Image Use Policy).

About this Image

These radio maps, obtained with the VLA, show 21 gravitational lenses discovered as part of CLASS (Cosmic Lens All-Sky Survey) plus a rediscovery of a previously known lens system. A gravitational lens is formed when a galaxy lies close to the line of sight to a more distant object - in these cases, a radio-loud quasar. The action of the galaxy's gravitational field bends the light from the distant object, forming multiple images of it. To find the systems pictured here, 16503 radio sources were examined with the VLA. Followup observations using radio (MERLIN and VLBA) telescopes and the Hubble Space Telescope in the optical were then used to confirm the systems as gravitational lenses. Systems normally have two images (e.g. 0218+357) or four images (e.g. 0712+472 where two images are blended and the fourth image is not quite visible in this discovery image). A few more exotic cases are also detected (e.g. six images in 1359+154). Each image is 3.2 arcseconds on a side, except for 2108+213 which is twice as big.

Investigator(s):  CLASS collaboration (University of Manchester, JBO; U. Pennsylvania; NRAO; Caltech; NFRA Dwingeloo; Leiden)

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Technical Data

    Telescope VLA 
    Date of Observation 1999-08-16 
    Type of Observation Continuum Observations 
    Band X 
    Wavelength 3.6 cm 
    Frequency 8.4 GHz 
    Center of Image RA: 24:00:0.00, Dec: 00:00:0.00 (J2000)  
    Field of View 0.0009 x 0.0009 degrees  
    Technical Caption These images are the 22 gravitational lenses found from 30-second A-configuration snapshots at 8.4 GHz of 16503 flat-spectrum radio sources. The intrinsically simple, quasi-pointlike structure of such sources allows easy detection of multiple-image gravitational lensing and also allows it to be distinguished from intrinsic structure such as small jets by subsequent observations at higher resolution. These images have a resolution of 220mas and were used to search for lens systems in the splitting range 0.3-15 arcseconds. (Bandwidth smearing prevents reliable searches beyond about 20-30 arcsec).  


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