A downturn in intergalactic CIV as redshift 6 is approached
Emma V. Ryan-Weber (1), Max Pettini (1), Piero Madau (2), Berkeley J., Zych (1) ((1) Institute of Astronomy, University of Cambridge; (2) Department, of Astronomy, Astrophysics, UC Santa Cruz)

TL;DR
This study presents the first evidence of a decline in intergalactic C IV metal density at redshifts above 5, indicating rapid metal build-up and changes in ionisation in the early universe.
Contribution
It provides the largest survey of intergalactic metals at z > 5 and reports the first detection of a decrease in C IV density at high redshift.
Findings
Omega(C IV) drops by a factor of 3.5 at z > 5
Number of C IV doublets is lower than expected for non-evolving absorbers
Metallicity of the IGM is estimated at 10^(-4) Z(Sun)
Abstract
We present the results of the largest survey to date for intergalactic metals at redshifts z > 5, using near-IR spectra of nine QSOs with emission redshifts z(em) > 5.7. We find, for the first time, a change in the comoving mass density of C IV ions as we look back to redshifts z > 5. At a mean <z> = 5.76, we deduce Omega(C IV)=(4.4+/-2.6)x10^(-9) which implies a drop by a factor of about 3.5 compared to the value at z < 4.7, after accounting for the differing sensitivities of different surveys. The observed number of C IV doublets is also lower by a similar factor, compared to expectations for a non-evolving column density distribution of absorbers. These results point to a rapid build-up of intergalactic C IV over a period of only 300 Myr; such a build-up could reflect the accumulation of metals associated with the rising levels of star formation activity from z = 9 indicated by…
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