Influence of microlensing on quasar statistics.
Abstract
The influence of microlensing on the statistics of multiply imaged QSOs is studied here by combining lens models for galaxies, responsible for the splitting of the QSO images, with local microlensing (hereafter ML) which provides every lensing image with a probability distribution of amplification factors. We find that the impact of ML on lensing statistics can be severe. In particular, the fraction of multiply imaged QSOs in a flux-limited sample can be seriously affected by ML due to the interplay of several effects: First, the finite probability for high amplification factors caused by ML enhances the amplification bias of lensed sources. Second, if the outer radii of the galaxies up to which they contain compact objects are large, QSOs can be highly amplified without their images being split, thus reducing the fraction of multiply imaged QSOs in a flux-limited sample. The clearest impact of ML on multiply imaged QSOs is the formation of a large fraction of lenses with a large flux ratio of the images if the flux threshold of the sample is high. We note that such lensing candidates have been detected recently. However, the occurrence of lensing candidates with large flux ratio of the images can also be explained by more realistic lensing models for the galaxies. In that case, the bright image should be a close pair of images. We estimate the typical separation of this pair and show that it should be resolved by the Space Telescope, thus providing a possible distinction between these two alternatives for the explanation of such high flux ratios. Some observational biases for the detection of the lensing galaxy are considered; in particular, we estimate the fraction of lens cases in which the galaxy is sufficiently bright to be observed and not outshined by the total flux from the QSO images. Our results are discussed in view of the simplicity of our model, thereby extracting those features which should remain valid if more sophisticated models (in particular for the galactic lenses) are considered.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- November 1990
- Bibcode:
- 1990A&A...239..113B
- Keywords:
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- Gravitational Lenses;
- Probability Distribution Functions;
- Quasars;
- Astronomical Models;
- Computational Astrophysics;
- Astrophysics