A Snapshot Survey for Gravitational Lenses among z>=4.0 Quasars. I. The z>5.7 Sample
Abstract
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.
- Publication:
-
The Astronomical Journal
- Pub Date:
- March 2004
- DOI:
- 10.1086/381906
- arXiv:
- arXiv:astro-ph/0309274
- Bibcode:
- 2004AJ....127.1305R
- Keywords:
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- Cosmology: Early Universe;
- Galaxies: Luminosity Function;
- Mass Function;
- Cosmology: Gravitational Lensing;
- Galaxies: Quasars: General;
- Galaxies: Quasars: Individual: Alphanumeric: SDSSp J104433.04-012502.2;
- quasars: individual (SDSSp J083643.85+005453.3);
- quasars: individual (SDSSp J130608.26+035626.3);
- quasars: individual (SDSSp J103027.10+052455.0);
- Astrophysics
- E-Print:
- 23 pages, 8 figures, 2 tables, submitted to AJ