New Quasars Detected via Variability in the QUEST1 Survey

Abstract

By observing the high galactic latitude equatorial sky in drift scan mode with the QUEST (QUasar Equatorial Survey Team) Phase 1 camera, multi-bandpass photometry on a large strip of sky, resolved over a large range of time scales (from hourly to biennially) has been collected. A robust method of ensemble photometry revealed those objects within the scan region that fluctuate in brightness at a statistically significant level. Subsequent spectroscopic observations of a subset of those varying objects easily discriminated the quasars from stars. For a 13-month time scale, 38% of the previously known quasars within the scan region were seen to vary in brightness and subsequent spectroscopic observation revealed that approximately 7% of all variable objects in the scan region are quasars. Increasing the time baseline to 26 months increased the percentage of previously known quasars which vary to 61% and confirmed via spectroscopy that 7% of the variable objects in the region are quasars. This reinforces previously published trends and encourages additional and ongoing synoptic searches for new quasars and their subsequent analysis. During two spectroscopic observing campaigns, a total of 30 quasars were confirmed, 11 of which are new discoveries and 19 of which were determined to be previously known. Using the previously cataloged quasars as a benchmark, we have found it possible to better optimize future variability surveys. This paper reports on the subset of variable objects which were spectroscopically confirmed as quasars.

22 pages, 3 figures, 4 tables. ApJ, submitted revised version: 19 pages, 4 figures, 2 tables, added clarifications, fixed typos, accepted by ApJ 24 Jan 2004

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• Variability selected high-redshift quasars on SDSS Stripe 82
• The dependence of quasar variability on black hole mass
• Rest-frame Optical Spectra and Black Hole Masses of 3<z<6 Quasars
• Mid-Infrared Variability from the Spitzer Deep, Wide-Field Survey
• A Synoptic, Multiwavelength Analysis of a Large Quasar Sample
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• Variability-selected QSO candidates in OGLE-II Galactic Bulge fields
• Extending the Eigenvector 1 Space to the Optical Variability of Quasars
• Exploring the Variable Sky with the Sloan Digital Sky Survey