New optical surveys for gravitationally lensed quasars

This thesis describes four new optical surveys for gravitationally lensed quasars. Three of these surveys take the form of traditional “targeted” searches. These include: (1)a ground-based survey targeting 173 radio-loud quasars using the 2.4 m telescope at Michigan-Dartmouth- <tfont>MIT</tfont> Observatory (<tfont>MDM</tfont>), producing one certain lens and one binary quasar; (2)a ground-based survey targeting 377 quasars in the southern hemisphere using the 1.5 m telescope at Cerro-Tololo Interamerican Observatory (CTIO), producing two certain lenses and one binary quasar; (3)a space-based snapshot survey for close separation lenses targeting 320 quasars using the Hubble Space Telescope (<tfont>HST</tfont>), producing three certain lenses and maybe a fourth. Of the eight systems discovered from these surveys, five are described in detail in this thesis. The first object, FBQ 1633+3134, is a 0^''_.7 double discovered from the <tfont>MDM</tfont> survey. Discrepant optical and radio flux ratios for this system means that it is most likely a physical binary quasar. The second, third and fourth objects—CTQ 414, HE 0230 2130, and CTQ 839—were all discovered from the <tfont>CTIO</tfont> survey. The former two systems are confirmed gravitational lenses, while the latter is a binary quasar. CTQ 414 is a 1^''_.2 double quasar that is well suited for future optical monitoring and a possible time-delay measurement, HE 0230-2130 is a complex four-image gravitational lens formed by two lensing galaxies, and CTQ 839 is almost certainly a binary quasar after repeated attempts to detect the hypothesized lensing galaxy have failed. The fifth system, the lensed quasar CTQ 327, is a 1^''_.2 double discovered from the <tfont>HST</tfont> survey which is also well suited for optical monitoring and a possible time-delay measurement. The superior angular resolution afforded by the HST snapshot survey is also used to constrain the matter density of any hypothetical population of dark, compact objects at high redshift to be less than 2.2% of the closure density for objects of mass 10^9.6 M_⊙ , and rules out a closure density of any compact object in the mass range 10^7.5 < M/ M_⊙ < 10^11.5 at the 99.7% confidence level. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.) (Abstract shortened by UMI.)