4.6. Targeted Searches
Finally, we briefly mention some targeted programs to identify high-redshift galaxies associated with distant quasars. A handful of galaxies within a few arcseconds of distant quasars have been identified at redshifts corresponding to damped Ly absorptions in the quasar spectra (e.g., Djorgovski et al. 1996). Searching for galactic companions to distant quasars has also proved successful. Djorgovski et al. (1985) report on an emission-line-selected source with a probable redshift of z = 3.218 associated with the quasar PKS 1614+051 at z = 3.209. More recent programs have used combinations of narrowband imaging and photometric color selection to search for quasar companions at z > 4. Several teams have identified companions to BR 1202-0725 at z = 4.695 (Djorgovski 1995; Hu, McMahon, & Egami 1996; Petitjean et al. 1996). Hu & McMahon (1996) report on two companions to BR 2237-0607 at z = 4.55. Djorgovski et al. (2000) presents a status report of an ongoing program to search for protoclusters around 20 quasars at z > 4. Preliminary results imply comoving number densities of protogalaxies 2-4 orders of magnitude higher than expected for the field. These results support biased galaxy formation models, in which galaxies preferentially form in the densest peaks of the primordial density field.