Quasar Detection via Variability in a High Galactic Latitude Drift-Scan Survey

This dissertation studies the intrinsic variability of quasars as a means of quasar detection. The detection of quasars via a parameter that is independent of quasar color allows for comparison with other color-selected samples of quasars, giving a more complete understanding of any possible selection effects in present and future quasar catalogs. Using the 16 CCD QUEST Phase 1 camera on the 1 m Schmidt telescope at the Venezuelan National Astronomical Observatory, 69 drift-scan observations of a high Galactic latitude region along the celestial equator were obtained. These observations, taken over the course of three observing seasons (1999 February–March, 2000 February–March, and 2001 March–April), cover the region between and , centered at a declination of 1 . h h m 10 15 30 Four broadband filters (B, V, and two R filters) were placed over the four rows of four CCDs, allowing the capture of four images of each object passing across the camera field of view. A large region of the sky ( ) was sampled over a range 2 194 deg of timescales (from hourly to biennially) for a duration of 26 months. This time sampling allows a region of the time domain distinct from other large sky surveys to be investigated. Following standard data reduction using a suite of custom software, incomplete ensemble photometry was used to correct for varying weather conditions and to compile a list of candidate objects that are variable at a statistically significant level. A confidence level for every object in each bandpass was calculated. An object was required to be variable at the 85% confidence level or greater in at least the two R filters to remain viable. Candidate lists were compiled from the data using both a 13 and 26 month time baseline. The quasars published in the ninth edition of the catalog of Veron-Cetty & Veron (2000, A Catalogue of Quasars and Active Galactic Nuclei [ESO Sci. Rep. 19; Garching: ESO]) were used to benchmark the variability characteristics of quasars over both timescales. After 13 months, 38% of the Veron-Cetty & Veron quasars within the survey were seen to vary at greater than the 85% confidence level. Utilizing the full 26 month baseline, 61% were variable at greater than the 85% confidence level. As expected, increasing the time baseline increased the percentage of known quasars in the field, which were seen to vary. A subset of the candidates on both timescales were chosen for spectroscopic confirmation. Low-resolution spectroscopy was obtained for these candidates in 2001 April and 2002 February using the Hydra multiobject spectrograph on the WIYN 3.5 m telescope at Kitt Peak National Observatory. Seventeen objects were confirmed as quasars by means of their distinctive broadened emission features during the 2001 April campaign. An additional 15 quasars, 2 of which overlap with the 2001 April spectroscopic campaign because of slight overlaps between two fields in each observing campaign, were discovered during the 2002 February campaign. As of 2003 October, 19 of the 30 discoveries were independently confirmed via a literature search, and 11 remain new discoveries (A. W. Rengstorf et al. 2004, in preparation). It is confirmed that increasing the time baseline of observations increases the completeness (i.e., the percentage of quasars that will be seen to vary) of the survey. While the density of candidate objects on the sky did not necessitate any cuts other than variability with regard to the number of available spectrograph fibers on Hydra, an a posteriori investigation into the broadband colors of the candidate objects reveal that color cuts in B–V and V–R would have increased the efficiency (i.e., the percentage of the candidate list that are quasars) of the spectroscopic confirmation.