Subaru spectroscopy of the giant Lyα nebula associated with the high-z powerful radio galaxy 1243+036

We report results of our new spatially resolved, optical spectroscopy of the giant Lyalpha nebula around a powerful radio galaxy, 1243+ 036 (4C + 03.24), at z = 3.57. The nebula is extended over similar to30 kpc from the nucleus and forms a pair of cones or elongated bubbles. The high-velocity (roughly - 1000 km s(-1); blueshifted with respect to the systemic velocity) Lyalpha-emitting components are detected at both sides of the nucleus along its major axis. The northwestern nebula is more spectacular in its velocity shift (blueshifted by - 1000 to - 1400 km s(-1)) and in its width (similar or equal to1900 km s(-1) FWHM) over similar or equal to30 kpc scale. We discuss possible origins of the nebula, such as ( 1) a shock-heated expanding bubble or outflowing cone associated with the superwind activity of the host galaxy, ( 2) halo gas photoionized by the anisotropic radiation from the active galactic nuclei (AGNs), and ( 3) a jet-induced star formation or shock. The last possibility may not be likely because Lyalpha emission is distributed out of the narrow channel of the radio jet. We show that the superwind model is most plausible since it can explain both the characteristics of the morphology ( size and shape) and the kinematical structures ( velocity shift and line width) of the nebula although the photoionization by AGNs may contribute to the excitation to some extent.