Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published September 2008 | Published
Journal Article Open

An exploratory search for z ≳ 6 quasars in the UKIDSS early data release


We conducted an exploratory search for quasars at z ~ 6-8, using the Early Data Release (EDR) from the United Kingdom Infrared Deep Sky Survey (UKIDSS) cross-matched to panoramic optical imagery. High-redshift quasar candidates are chosen using multi-color selection in i, z, Y, J, H, and K bands. After removal of apparent instrumental artifacts, our candidate list consisted of 34 objects. We further refined this list with deeper imaging in the optical for ten of our candidates. Twenty-five candidates were followed up spectroscopically in the near-infrared and in the optical. We confirmed 25 of our spectra as very low-mass main-sequence stars or brown dwarfs, which were indeed expected as the main contaminants of this exploratory search. The lack of quasar detection is not surprising: the estimated probability of finding a single z > 6 quasar down to the limit of UKIDSS in 27.3 deg^2 of the EDR is <5%. We find that the most important limiting factor in this work is the depth of the available optical data. Experience gained in this pilot project can help refine high-redshift quasar selection criteria for subsequent UKIDSS data releases.

Additional Information

© 2008 The American Astronomical Society. Received 2007 July 17; accepted 2008 May 25; published 2008 July 31. We thank Dr. K. Cruz for lending her expertise in lowmass stars to this paper. We are grateful to the staff of W. M. Keck observatory for their assistance during our remote observing runs. This work was supported in part by the NSF grant AST-0407448 and by the Ajax foundation. This research has made use of data obtained from or software provided by the U.S. National Virtual Observatory, which is sponsored by the National Science 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.

Attached Files

Published - GLIaj08.pdf


Files (660.5 kB)
Name Size Download all
660.5 kB Preview Download

Additional details

August 22, 2023
October 18, 2023