  In order to search for metals in the Lyman alpha forest at redshifts z > 4,
we have obtained spectra of high S/N and resolution of three QSOs at z > 5.4
discovered by the Sloan Digital Sky Survey. These data allow us to probe to
metal enrichment of the intergalactic medium at early times with higher
sensitivity than previous studies. We find 16 C IV absorption systems with
column densities log N(C IV) = 12.50 - 13.98 over a total redshift path Delta X
= 3.29. In the redshift interval z = 4.5-5.0, where our statistics are most
reliable, we deduce a comoving mass density of C IV ions Omega(C IV) = (4.3 +/-
2.5) x 10(-8) (90% confidence limits) for absorption systems with log N(C IV) >
13.0 (for an Einstein-de Sitter cosmology with h = 0.65). This value of Omega(C
IV) is entirely consistent with those measured at z < 4; we confirm the earlier
finding by Songaila (2001) that neither the column density distribution of C IV
absorbers nor its integral show significant redshift evolution over a period of
time which stretches from 1.25 to 4.5 Gyr after the big bang. This somewhat
surprising conclusion may be an indication that the intergalactic medium was
enriched in metals at redshifts much greater than 5, perhaps by the sources
responsible for its reionization. Alternatively, the C IV systems we see may be
associated with outflows from massive star-forming galaxies at later times,
while the truly intergalactic metals may reside in regions of the Lyman alpha
forest of lower density than those probed up to now.
