SPATIALLY RESOLVED GAS KINEMATICS WITHIN A Lyα NEBULA: EVIDENCE FOR LARGE-SCALE ROTATION

We use spatially extended measurements of Ly alpha as well as less optically thick emission lines from an approximate to 80 kpc Ly alpha nebula at z approximate to 1.67 to assess the role of resonant scattering and to disentangle kinematic signatures from Ly alpha radiative transfer effects. We find that the Ly alpha, CIV, HeII, and C III] emission lines all tell a similar story in this system, and that the kinematics are broadly consistent with large-scale rotation. First, the observed surface brightness profiles are similar in extent in all four lines, strongly favoring a picture in which the Ly alpha photons are produced in situ instead of being resonantly scattered from a central source. Second, we see low kinematic offsets between Ly alpha and the less optically thick He II line (similar to 100-200 km s(-1)), providing further support for the argument that the Ly alpha and other emission lines are all being produced within the spatially extended gas. Finally, the full velocity field of the system shows coherent velocity shear in all emission lines: similar to 500 km s(-1) over the central approximate to 50 kpc of the nebula. The kinematic profiles are broadly consistent with large-scale rotation in a gas disk that is at least partially stable against collapse. These observations suggest that the Ly alpha nebula represents accreting material that is illuminated by an offset, hidden active galactic nucleus or distributed star formation, and that is undergoing rotation in a clumpy and turbulent gas disk. With an implied mass of M(< R = 20 kpc) similar to 3x10(11) M-circle dot, this system may represent the early formation of a large Milky Way mass galaxy or galaxy group.