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Magnification of light from many distant quasars by gravitational lenses

Nature volume 417, pages 923–925 (2002)Cite this article

Abstract

Exceptionally bright quasars with redshifts up to z = 6.28 have recently been discovered1. Quasars are thought to be powered by the accretion of gas onto supermassive black holes at the centres of galaxies. Their maximum (Eddington) luminosity depends on the mass of the black hole, and the brighter quasars are inferred to have black holes with masses of more than a few billion solar masses. The existence of such massive black holes poses a challenge to models for the formation of structures in the early Universe2,3, as it requires their formation within one billion years of the Big Bang. Here we show that up to one-third of known quasars with z ≈ 6 will have had their observed flux magnified by a factor of ten or more, as a consequence of gravitational lensing by galaxies along the line of sight. The inferred abundance of quasar host galaxies, as well as the luminosity density provided by the quasars, has therefore been substantially overestimated.

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Figure 1: Enhancement in the co-moving space density of host galaxies for quasars at z = 6 as a function of the magnification due to lensing, μ.
Figure 2: The probability of observing a magnification larger than μobs for a quasar at a redshift z = 6 in a sample with a magnitude limit z* < 20.2.

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Acknowledgements

We thank E. Turner, J. Winn and R. Barkana for discussions. This work was supported in part by grants from the NSF and NASA. J.S.B.W. is supported by a Hubble Fellowship.

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  1. Astronomy Department, Harvard University, 60 Garden Street, Cambridge, Massachusetts, 02138, USA

    J. Stuart B. Wyithe & Abraham Loeb

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Correspondence to Abraham Loeb.

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Wyithe, J., Loeb, A. Magnification of light from many distant quasars by gravitational lenses. Nature 417, 923–925 (2002). https://doi.org/10.1038/nature00794

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