Evolution of Lyman Break Galaxies beyond z = 4

The formation rate of luminous galaxies seems to be roughly constant from z approximately 2 to approximately 4 from the recent observations of Lyman break galaxies (LBGs). The abundance of luminous quasars, on the other hand, appears to drop off by a factor of more than 20 from z approximately 2 to z approximately 5. The difference in evolution between the two classes of objects in the overlapping, observed redshift range (z=2-4) can be explained naturally if we assume that quasar activity is triggered by mergers of luminous LBGs and one quasar lifetime is approximately 107-108 yr. If this merger scenario holds at higher redshift, for the evolutions of these two classes of objects to be consistent at z>4, the formation rate of luminous LBGs is expected to drop off at least as rapidly as exp-&parl0;z-4&parr0;6&solm0;5 at z>4.