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Published June 10, 2007 | Published
Journal Article Open

Discovery of a Probable Physical Triple Quasar


We report the discovery of the first known probable case of a physical triple quasar. A previously known double system, QQ 1429-008 at z = 2.076, is shown to contain a third, fainter QSO component at the same redshift. Deep optical and IR imaging has failed to reveal a plausible lensing galaxy group or a cluster, and we are unable to construct any viable lensing model that could lead to the observed distribution of source positions and relative intensities of the three QSO image components. There are also hints of differences in the broadband spectral energy distributions of the different components, which are more naturally understood if they are physically distinct active galactic nuclei (AGNs). Therefore, we conclude that this system is most likely a physical triple quasar, the first such close QSO grouping known at any redshift. The projected component separations are ~30-50 kpc, typical of interacting galaxy systems. The existence of this highly unusual system supports the standard picture in which galaxy interactions lead to the onset of QSO activity.

Additional Information

© 2007 The American Astronomical Society. Received 2006 December 22; accepted 2007 April 25; published 2007 May 22. We are grateful to the staff of the W. M. Keck and ESO-VLT observatories for their expert assistance in the course of our observing runs, and to M. Pahre with assistance from some of the Keck observations. The Keck data used in this Letter were obtained in a collaborative project involving J. Cohen, B. T. Soifer, R. Blandford, G. Neugebauer, and I. Smail. S. G. D., A. M., and E. G. acknowledge partial support from NSF grant AST-0407448 and from the Ajax Foundation. F. C., G. M., and D. S. are financially supported by the Swiss National Science Foundation (SNSF). S. G. D. acknowledges the hospitality of EPFL and the Geneva Observatory, where some of this work was performed.

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