Intergalactic C iv absorption at redshifts 5.4 to 6

Abstract We report the discovery of a strong C ivλλ1548, 1550 absorption system at zabs= 5.7238 in the near-infrared spectrum (J-band) of the zem= 6.28 QSO SDSS J1030+0524. These observations, obtained with the Infrared Spectrometer And Array Camera (ISAAC) on the European Southern Observatory Very Large Telescope (ESO VLT), demonstrate that, with modern instrumentation, QSO absorption line spectroscopy can be successfully extended to near-infrared wavelengths to probe the intergalactic medium near the end of the reionization epoch. Although the statistics of this pilot study are limited, the mass density of triply ionized carbon implied by our data is comparable to the values of ΩC IV reported at lower redshifts. 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 to 4.5 Gyr after the big bang, suggesting that a large fraction of intergalactic metals may already have been in place at redshifts above 6. Alternatively, the strong C iv system we have detected may be associated with outflowing, highly-ionized, gas from a foreground massive galaxy; deep imaging and spectroscopy of galaxies near the QSO sightline should be able to distinguish between these two possibilities.