High-Redshift Quasars as Probes of Primordial Large-Scale Structure and   Galaxy Formation
  Several arguments suggest that quasars at z > 4 may be in the cores of future giant ellipticals, and forming at the very highest peaks of the primordial density field. A strong bias-driven primordial clustering is then expected in these fields, which are naturally interpreted as the cores of future rich clusters. High-redshift quasars can thus be used as markers of some of the earliest galaxy formation sites. Recent discoveries of (proto)galaxy companions of z > 4 quasars, and hints of strong clustering among high-z quasars give some support to this idea. The frequency of companions is much higher than is expected for a general field, or the upper limits for comparable redshifts in the HDF. Clustering of quasars themselves at z > 3 or 4 may reflect the primordial large-scale structure. 
S. G. Djorgovski (Palomar Observatory, Caltech, Pasadena, CA)