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We examine the absorption line spectra of a sample of 31 luminous (M_UV=-23)Lyman break galaxies at redshift z~6 using data taken with the FOCAS and OSIRISspectrographs on the Subaru and GTC telescopes. For two of these sources wepresent longer exposure data taken at higher spectral resolution from ESO'sX-shooter spectrograph. Using these data, we demonstrate the practicality ofstacking our lower resolution data to measure the depth of various interstellarand stellar absorption lines to probe the covering fraction of low ionizationgas and the gas-phase and stellar metallicities near the end of the era ofcosmic reionization. From maximum absorption line depths of SiII1260 andCII1334, we infer a mean covering fraction of >0.85+/-0.16 for our sample. Thisis larger than that determined using similar methods for lower luminositygalaxies at slightly lower redshifts, suggesting that the most luminousgalaxies appear to have a lower escape fraction than fainter galaxies, andtherefore may not play a prominent role in concluding reionization. Usingvarious interstellar absorption lines we deduce gas-phase metallicities closeto solar indicative of substantial early enrichment. Using selected stellarabsorption lines, we model our spectra with a range of metallicities usingtechniques successfully employed at lower redshift and deduce a stellarmetallicity of 0.4 +0.3/-0.1 solar, consistent with the stellar mass - stellarmetallicity relation recently found at z~3-5. We discuss the implications ofthese metallicity estimates for the typical ages of our luminous galaxies andconclude our results imply initial star formation at redshifts z~10, consistentwith independent analyses of earlier objects.

The Mean Absorption Line Spectra of a Selection of Luminous z~6 Lyman Break Galaxies