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Published August 20, 2010 | Published
Journal Article Open

Binary Quasars at High Redshift. I. 24 New Quasar Pairs at z ~ 3-4


The clustering of quasars on small scales yields fundamental constraints on models of quasar evolution and the buildup of supermassive black holes. This paper describes the first systematic survey to discover high-redshift binary quasars. Using color-selection and photometric redshift techniques, we searched 8142 deg^2 of Sloan Digital Sky Survey imaging data for binary quasar candidates, and confirmed them with follow-up spectroscopy. Our sample of 27 high-redshift binaries (24 of them new discoveries) at redshifts 2.9 < z < 4.3 with proper transverse separations 10 kpc < R⊥ < 650 kpc increases the number of such objects known by an order of magnitude. Eight members of this sample are very close pairs with R < 100 kpc, and of these close systems four are at z>3.5. The completeness and efficiency of our well-defined selection algorithm are quantified using simulated photometry and we find that our sample is ~50% complete. Our companion paper uses this knowledge to make the first measurement of the small-scale clustering (R < 1 h^(–1) Mpc comoving) of high-redshift quasars. High-redshift binaries constitute exponentially rare coincidences of two extreme (M ≳ 10^9 M_☉) supermassive black holes. At z ~ 4, there is about one close binary per 10 Gpc^3, thus these could be the highest sigma peaks, the analogs of superclusters, in the early universe.

Additional Information

© 2010 American Astronomical Society. Received 2009 August 31; accepted 2010 January 2; published 2010 August 3. We acknowledge helpful discussions with J. Cohn, N. Padmanabhan, D. Schlegel, D. Weinberg, A. Wetzel, and M. White. For part of this work, J.F.H. was supported by a NASA Hubble Fellowship grant no. 01172.01-A and by the NSF Postdoctoral Fellowship program (AST-0702879). Y.S. and M.S. acknowledge support from the National Science Foundation (NSF) (AST-0707266). D.P.S. similarly acknowledges support from the NSF (AST-0607634). S.G.D., A.A.M., and E.G. acknowledge partial support from the NSF grant AST- 0407448 and from the Ajax Foundation. C.L.M. acknowledges support from the Packard Foundation and the NSF (AST-0808161). Funding for the SDSS and SDSS-II has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England. The SDSS Web Site is http://www.sdss.org/. The SDSS is managed by the Astrophysical Research Consortium for the Participating Institutions. The Participating Institutions are the American Museum of Natural History, Astrophysical Institute Potsdam, University of Basel, University of Cambridge, Case Western Reserve University, University of Chicago, Drexel University, Fermilab, the Institute for Advanced Study, the Japan Participation Group, Johns Hopkins University, the Joint Institute for Nuclear Astrophysics, the Kavli Institute for Particle Astrophysics and Cosmology, the Korean Scientist Group, the Chinese Academy of Sciences (LAMOST), Los Alamos National Laboratory, theMax-Planck- Institute for Astronomy (MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico State University, Ohio State University, University of Pittsburgh, University of Portsmouth, Princeton University, the United States Naval Observatory, and the University of Washington. Some of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. The authors recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community.We are most fortunate to have the opportunity to conduct observations from this mountain.

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August 22, 2023
October 20, 2023