2005A&A...440L..51M

We report the detection of the ²P_3/2->²P_1/2 fine-structure line of C⁺ at 157.74µm in SDSS J114816.64+525150.3 (hereafter J1148+5251), the most distant known quasar, at z=6.42, using the IRAM 30-m telescope. This is the first detection of the [CII] line at high redshift, and also the first detection in a Hyperluminous Infrared Galaxy (L_FIR>10¹³L_☉). The [CII] line is detected at a significance level of 8σ and has a luminosity of 4.4x10⁹L_☉. The L_[CII]/L_FIR ratio is 2x10^–4, about an order of magnitude smaller than observed in local normal galaxies and similar to the ratio observed in local Ultraluminous Infrared Galaxies. The [CII] line luminosity indicates that the host galaxy of this quasar is undergoing an intense burst of star formation with an estimated rate of ≃3000M_☉/yr. The detection of C⁺ in SDSS J1148+5251 suggests a significant enrichment of metals at z∼6 (age of the universe ∼870Myr), although the data are consistent with a reduced carbon to oxygen ratio as expected from chemical evolutionary models of the early phases of galaxy formation.