We present deep Hubble Space Telescope and Spitzer Space Telescope observations of the host galaxy of GRB 050904 at z = 6.295 .
The host is detected in the H -band and marginally at 3.6 \mu m. From these detections , and limits in the z ^ { \prime } -band and 4.5 \mu m , we infer an extinction-corrected absolute magnitude , M _ { UV } \approx - 20.7 mag , or \sim L * , a substantial star formation rate of \sim 15 M _ { \odot } yr ^ { -1 } , and a stellar mass of { few } \times 10 ^ { 9 } M _ { \odot } .
A comparison to the published sample of spectroscopically-confirmed galaxies at z > 5.5 reveals that the host of GRB 050904 would evade detection and/or confirmation in any of the current surveys due to the lack of detectable Ly \alpha emission , which is likely the result of dust extinction ( A _ { 1200 } \sim 1.5 mag ) .
This suggests that not all luminous starburst galaxies at z \sim 6 are currently being accounted for .
Most importantly , using the metallicity of Z \approx 0.05 Z _ { \odot } inferred from the afterglow absorption spectrum , our observations indicate for the first time that the observed evolution in the mass- and luminosity-metallicity relations from z = 0 to z \sim 2 continues on to z > 6 .
The ease of measuring redshifts and metallicities from the afterglow emission suggests that in tandem with the next generation ground- and space-based telescopes , a GRB mission with dedicated near-IR follow-up can provide unique information on the evolution of stars and galaxies through the epoch of re-ionization .