Subaru Spectroscopy of the Giant Ly Nebula Associated with the High-zPowerful Radio Galaxy 1243+036

We report results of our new spatially-resolved, optical spectroscopy of thegiant Ly$\alpha$ nebula around a powerful radio galaxy 1243+036 (4C+03.24) at$z=3.57$. The nebula is extended over $\sim 30$ kpc from the nucleus, and formsa pair of cones or elongated bubbles. The high-velocity ($\sim -1000$ kms$^{-1}$; blueshifted with respect to the systemic velocity)Ly$\alpha$-emitting components are detected at both sides of the nucleus alongits major axis. The northwestern nebula is more spectacular in its velocityshift (blueshifted by -1000 km s$^{-1}$ to -1400 km s$^{-1}$) and in its width($\simeq 1900$ km s$^{-1}$ FWHM) over $\simeq 30$ kpc scale. We discusspossible origin of the nebula; 1) the shock-heated expanding bubble oroutflowing cone associated with the superwind activity of the host galaxy, 2)halo gas photoionized by the anisotropic radiation from the active galacticnuclei (AGN), and 3) the jet-induced star-formation or shock. The lastpossibility may not be likely because Ly$\alpha$ emission is distributed out ofthe narrow channel of the radio jet. We show that the superwind model is mostplausible since it can explain both the characteristics of the morphology (sizeand shape) and the kinematical structures (velocity shift and line width) ofthe nebula although the photoionization by AGN may contribute to the excitationto some extent.Comment: 12 pages, 2 figures, accepted for publication in A