Properties of a High-Redshift Galaxy at [ITAL]z[/ITAL] = 4.4

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Abstract
We discuss the absorption properties of a high-redshift galaxy at z = 4.3829 identified as a damped Lyα system in the Keck spectrum of the quasar BRI 1202-0725 (zem = 4.7). This is at present the highest redshift damped Lyα system known, observed when the age of the universe was only 1 Gyr (q0 = 0.5, H0 = 50). Both the high redshift and low metallicity ([Fe/H] = -2.2) of the system indicate that it is an extremely young galaxy in an early stage of evolution. The relative elemental abundance patterns are consistent with extreme Population II metallicities, providing evidence for enrichment by Type II supernovae only. Kinematic evidence suggests that the absorbing galaxy may be a massive spiral. We discuss the implications of this result on theories of galaxy formation. The Si IV and C IV absorption in the system appears unusually weak. Several plausible explanations are provided. We estimate T < 19.6 K for the cosmic microwave background radiation at z = 4.3829, which is consistent with the predicted temperature of 14.7 K from the big bang cosmology.