Detection of weak lensing by a massive dark halo in Q2345+007

Details Detection of weak lensing by a massive dark halo in Q2345+007 Detection of weak lensing by a massive dark halo in Q2345+007

Dec 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...280l...7b&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 280, no. 1, p. L7-L10

Astronomy and Astrophysics

Astrophysics

41

Galactic Clusters, Galactic Evolution, Galactic Halos, Gravitational Fields, Gravitational Lenses, Quasars, Shearing, Astronomical Photometry, Cosmology, Dark Matter, Missing Mass (Astrophysics), Red Shift

Scientific paper

We report the detection of several arclets, a small arc, and a coherent gravitational shear field centered on the vicinity of two bright galaxies, approximately 45 sec away from the double quasar 2345+007. In addition we discovered a new QSO at z = 2.653 and at approximately 2 min from the center indicated by the shear. The shear is found from weak distortion of background galaxies and is representative of a cluster-like mass. This suggests a possibility that 2345+007 A, B are two images of the same source, split by a cluster-like mass. The two galaxies have redshift z = 0.28, and the field is too poor in bright galaxies to indicate a rich cluster at this redshift. In addition, if there were a cluster-like (dark) mass at z = 0.25 with a critical line passing between the A and B QSO images, the shear field would be significantly stronger than what we observe. However, deep images show a small excess of faint blue galaxies in the area on which the coherent shear is centered. Thus, it is possible that a rich cluster at a higher redshift induces the coherent shear. In this case, it would be able to produce a critical line between A and B of 2345+007. To our knowledge, this is the first direct measurement of a weak shear near a double quasar. We find that this is a powerful technique to locate large masses on lines of sight, even where concentrations of galaxies are not previously discovered. In particular, this technique will enable us to detect hypothetical concentrations of dark matter which are not traced by galaxies. It can also provide a new efficient approach to the problem of large scale quasar-galaxy associations, raised by Fugmann (1990) and Bartelmann & Schneider (1993).

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