Gravitational Lensing of High Redshift Sources

Abstract

The combination of deep exposures and high resolution offered by telescopes in space allows the detection of lensing over a wide range of source redshifts and lens masses. As an example, we model a lens candidate found in the southern Hubble Deep Field. The system consists of a source galaxy lensed into an arc, 0."9 from an elliptical galaxy. The photometric redshift of 0.6 for the lens galaxy implies a mass-to-light ratio of 15 in solar units, out to three effective radii. This lens system may be a preview of the large number of lensed high-redshift galaxies that will be detected with the Next Generation Space Telescope (NGST). When NGST is launched in the next decade, some of the earliest galaxies and quasars in the Universe may be observed. Popular models of structure formation imply that at a given observed flux, roughly 3% of redshift > 5 sources are multiply imaged. Thus, NGST should detect several lensed objects in each field of view. In addition, NGST will be a valuable tool for weak lensing measurements, as long as it can resolve the background galaxies. We estimate the angular size distribution of high redshift sources within hierarchical models of structure formation and find that most will be resolved by NGST even at z > 10.

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