A snapshot survey for gravitational lenses among z ≥ 4.0 quasars. I. The z > 5.7 sample

Gordon T. Richards, Michael A. Strauss, Bartosz Pindor, Zoltán Haiman, Xiaohui Fan, Daniel Eisenstein, Donald P. Schneider, Neta A. Bahcall, J. Brinkmann, Robert Brunner

Research output: Contribution to journalReview articlepeer-review

47 Scopus citations


Over the last few years, the Sloan Digital Sky Survey (SDSS) has discovered several hundred quasars with redshift between 4.0 and 6.4. Including the effects of magnification bias, one expects a priori that an appreciable fraction of these objects are gravitationally lensed. We have used the Advanced Camera for Surveys on the Hubble Space Telescope to carry out a snapshot imaging survey of high-redshift SDSS quasars to search for gravitationally split lenses. This paper, the first in a series reporting the results of the survey, describes snapshot observations of four quasars at z = 5.74, 5.82, 5.99, and 6.30, respectively. We find that none of these objects has a lensed companion within 5 mag with a separation larger than 0″3; within 2.5 mag we can rule out companions within 0″.1. Based on the nondetection of strong lensing in these four systems, we constrain the z ~ 6 luminosity function to a slope of β > -4.63 (3 σ), assuming a break in the quasar luminosity function at M* 1450 = -24.1. We discuss the implications of this constraint on the ionizing background due to quasars in the early universe. Given that these quasars are not highly magnified, estimates of the masses of their central engines by the Eddington argument must be taken seriously, possibly challenging models of black hole formation.

Original languageEnglish (US)
Pages (from-to)1305-1312
Number of pages8
JournalAstronomical Journal
Issue number3 1779
StatePublished - Mar 2004


  • Early universe
  • Galaxies: luminosity function, mass function
  • Gravitational lensing
  • Quasars: general
  • Quasars: individual (SDSSp J104433.04-012502.2, SDSSp J083643.85+005453.3, SDSSp J130608.26+035626.3, SDSSp J103027.10+052455.0)

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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