CONSTRAINTS ON THE UNIVERSAL C IV MASS DENSITY ATz∼ 6 FROM EARLY INFRARED SPECTRA OBTAINED WITH THE MAGELLAN FIRE SPECTROGRAPH

We present a new determination of the intergalactic C IV mass density at 4.3 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 C IV 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 C IV at z = 5.82 is re-identified as Mg II at z = 2.78, leading to a substantial downward revision in Ωsubscript C IV for these prior studies. Additionally, we confirm the presence of at least two systems with low-ionization C II, Si II, and O I absorption but relatively weak signal from C IV. The latter systems may be of interest if the downward trend in Ωsubscript C IV at high redshift is driven in part by ionization effects.