|
In each spectroscopic observation, we will devote between one-tenth and one-sixth of the fibers to a survey of quasar candidates. These are defined as stellar objects with colors well separated from the stellar locus.
The cumulative quasar counts in pi steradians as a function of B magnitude are given in Table 3.3.1. The data are based on the results of Crampton, Cowley, and Hartwick (1987; cf., La Franca and Christiani 1996). Quasars on our system have g' ~ B - 0.3 , but the transformation is affected at the level of several tenths of a magnitude at different redshifts by the emission lines. We give approximate g' values in the table.
Table 3.3.1: Quasars in pi Steradians |
B |
g' |
N(<B) |
16 |
15.7 |
100 |
17 |
16.7 |
1300 |
18 |
17.7 |
11300 |
19 |
18.7 |
52900 |
20 |
19.7 |
172000 |
21 |
20.7 |
414000 |
The estimated limiting magnitude for obtaining redshifts of quasars with the proposed survey telescope is g' ~ 19.7 . One can go significantly fainter with quasars than galaxies for two reasons (Section 5.2.1): quasars, being point sources, have a larger fraction of their light captured by the fibers than do galaxies, and redshifts for quasars will be based on measurements of strong emission lines, whereas in most cases one must rely on absorption features to determine redshifts for galaxies.
The proposed instrumentation of the Sloan Digital Sky Survey will therefore allow detailed study of the order of 100,000 quasars brighter than g' ~ 19.7 . For comparison, the largest samples of quasars from individual surveys compiled in the last decade (cf., Hartwick and Schade 1990; La Franca and Christiani 1996, for reviews) include the works of Boyle, Shanks, and Peterson (1988) (423 quasars with z < 2.2), Hewett, Foltz, and Chaffee (1995) (1055 quasars with z < 3.4), Warren et al. (1991a,b, 1994) (85 quasars with 2.2 < z < 4.5), Schneider, Schmidt, and Gunn (1994) (140 quasars with 2.1 < z < 4.8), Christiani et al. (1995) and La Franca and Christiani (1996) (327 quasars with z < 2.2 ). The large, well-defined data base produced by the SDSS can be used to address many pressing questions concerning the nature of quasars, their evolution, quasar clustering, galaxy formation at high redshifts, and the properties of the intergalactic medium. |
