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Astron. Astrophys. 320, 8-12 (1997)

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3. Possible interpretations

There are in principle three possible explanations for these phenomena.

1. In the framework of standard cosmology an enhancement of the number of close pairs with discordant redshifts can be obtained if the two-point correlation function extends over distances corresponding to the redshift differences. However, the redshift differences in Table 1 are so large that none of the presently discussed cosmologies would predict any appreciable correlations in these cases.

2. The results taken at their face value indicate that significant parts of the redshifts have a non-cosmological origin (cf. for example Burbidge 1996) and the pairs are physically associated.

3. Back to the cosmological interpretation, it must be argued that a local enhancement of the QSO density in some part of the sky can be caused by gravitational lensing which affects the apparent magnitude of QSOs and can lead to the preferential inclusion of lensed QSOs into flux-limited samples.

Since (1) is clearly ruled out, we are left with (2) and (3). The authors of this paper have divergent views about the likelihood that (2) or (3) is the explanation. Much evidence for the existence of non-cosmological redshifts has been discussed elsewhere (Hoyle & Burbidge 1996; Burbidge 1996).

Thus we turn to (3) and discuss what can be said in favor of a gravitational lensing scenario.

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© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998