Exploring the Structure of Distant Galaxies with Adaptive Optics on the Keck II Telescope

We report on the first observation of cosmologically distant field galaxieswith an high order Adaptive Optics (AO) system on an 8-10 meter classtelescope. Two galaxies were observed at 1.6 microns at an angular resolutionas high as 50 milliarcsec using the AO system on the Keck-II telescope. Radialprofiles of both objects are consistent with those of local spiral galaxies andare decomposed into a classic exponential disk and a central bulge. Astar-forming cluster or companion galaxy as well as a compact core are detectedin one of the galaxies at a redshift of 0.37+/-0.05. We discuss possibleexplanations for the core including a small bulge, a nuclear starburst, or anactive nucleus. The same galaxy shows a peak disk surface brightness that isbrighter than local disks of comparable size. These observations demonstratethe power of AO to reveal details of the morphology of distant faint galaxiesand to explore galaxy evolution.Comment: 5 pages, Latex, 3 figures. Accepted for publication in P.A.S.