Annu. Rev. Astron. Astrophys. 1992. 30: 311-358
Copyright © 1992 by . All rights reserved


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2. SECURE LENSES

To date, three distinct classes of multiple imaging have been identified: multiple quasars (i.e. double, triple, and quadruple images of a single quasar), arcs (images of high redshift galaxies formed by clusters), and radio rings (images of extended radio sources formed by intervening galaxies). Unfortunately, the criteria for class membership remain subjective and no list commands universal acceptance. [For instance, a problem with identifying multiply-imaged quasars is that distinct objects can have quite similar spectra (Phinney & Blandford 1986, Bahcall et al. 1986, Shaver 1986); conversely, small spectral differences can be attributed to time variability (Filippenko 1989, Steidel & Sargent 1991).] Adopting the most conservative of conditions, we list in Table 1 the ``secure'' cases in each of the three classes of lensing.

Table 1. Secure cases of multiple-imaging gravitational lenses

Source zs zd thetamax

Multiple Quasars
Q0957+561AB 1.41 0.36 6.1"
Q0142-100AB 2.72 0.49 2.2"
Q2016+112ABC 3.27 1.01 3.8"
Q0414+053ABCD 2.63 ? 3"
Q1115+080A1A2BC 1.72 ? 2.3"
H1413+117ABCD 2.55 ? 1.1"
Q2237+031ABCD 1.69 0.039 1.8"
Arcs
Abell 370 0.72 0.37
Abell 963 0.77 0.21
Abell 1352 ? 0.28
Abell 1525 ? 0.26
Abell 1689 ? 0.18
Abell 2163 ? 0.17
Abell 2218 ? 0.17
Abell 2390 0.92 0.23
Cl 0024+17 ? 0.39
Cl 0302+17 ? 0.42
Cl 0500-24 0.91 0.32
Cl 1409+52 ? 0.46
Cl 2244-02 2.23 0.33
Radio Rings
MG1131+0456 ? ? 2.2"
0218+357 ? ? 0.3"
MG1549+3047 ? 0.11 1.8"
MG1634+1346 1.75 0.25 2.1"
1830-211 ? ? 1.0"

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