CONSTRAINTS ON THE UNIVERSAL CIV MASS DENSITY AT z ∼ 6 FROM EARLY INFRARED SPECTRA OBTAINED WITH THE MAGELLAN FIRE SPECTROGRAPH

We present a new determination of the intergalactic CIV mass density at 4.3 < z < 6.3. Our constraints are derived from high signal-to-noise spectra of seven quasars at z > 5.8 obtained with the newly commissioned Folded-Port Infrared Echellette (FIRE) spectrograph on the Magellan Baade telescope, coupled with six observations of northern objects taken from the literature. We confirm the presence of a downturn in the CIV abundance at < z > = 5.66 by a factor of 4.1 relative to its value at < z > = 4.96, as measured in the same sight lines. In the FIRE sample, a strong system previously reported in the literature as CIV at z = 5.82 is re-identified as MgII at z = 2.78, leading to a substantial downward revision in Omega(CIV) for these prior studies. Additionally, we confirm the presence of at least two systems with low-ionization CII, SiII, and OI absorption but relatively weak signal from CIV. The latter systems may be of interest if the downward trend in Omega(CIV) at high redshift is driven in part by ionization effects.