4.7. Summary

In Table 5 we summarize the surface densities measured (estimated) from the various search techniques described above. We see that the nonoptical search techniques have very low surface densities, most spectacularly for GRBs whose surface density is 10 per year per Hubble volume. The optical/near-IR techniques which are sensitive to normal, star-forming galaxies typically have surface densities of a few per square arcminute per unit redshift. In Section 6 we consider the biases in the different techniques and discuss how independent the methods may be.

Table 5. Surface Densities of High-Redshift Galaxies

Technique	z Range	Sources arcmin-2	Limiting Flux Density	Reference
Radio sources...	All	0.03	S1.4 GHz > 1 mJy	1
Submillimeter galaxies...	All	0.09	S850 µm > 2 mJy	2
X-ray sources...	All	0.27 ± 0.04	10-15 ergs cm-2 s-1	3
GRBs...	All	10-7 yr-1	...
Lyman-break galaxies...	~ 3	0.68 ± 0.02	RAB 25.0	4
Lyman-break galaxies...	~ 4	0.21 ± 0.02	IAB 25.0	4
Photometric candidates...	4.5-5.5	1.0 (unit-z)-1	I814AB 26.5	5
Narrowband surveys, CADIS...	~ 5.75	0.2 (unit-z)-1	5.0 × 10-17 ergs cm-2 s-1 (5 )	6
Narrowband surveys, Hawaii...	~ 4.6	3 (unit-z)-1	1.5 × 10-17 ergs cm-2 s-1 (5 )	7
Grism survey, NICMOS...	0.7-1.9	0.5	2.0 × 10-17 ergs cm-2 s-1	8
Serendip survey, Berkeley...	4.5-5.5	2 ± 1 (unit-z)-1	1.0 × 10-17 ergs cm-2 s-1 (5 )	9
REFERENCES. - (1) Becker et al. 1995; (2) Hughes et al. 1998; (3) Hasinger et al. 1998; (4) Steidel et al. 1999; (5) Fernàndez-Soto et al. 1999; (6) Thommes et al. 1998; (7) Cowie & Hu 1998; (8) McCarthy et al. 1999; (9) Stern et al. 1999a.