Subaru Deep Spectroscopy of a Star-forming Companion Galaxy of BR 1202−0725 at z = 4.7

We present deep spatially resolved optical spectroscopy of the northwest companion galaxy of the quasar BR 1202-0725 at z = 4.7. Its rest-frame UV spectrum shows star-forming activity in the nuclear region. The Lyα emission profile is symmetric with wavelength, while its line width is unusually wide (FWHM ≃ 1100 km s-1) for such a high-z star-forming galaxy. The spectrum taken along the Lyα nebula elongation, which is almost along the minor axis of the companion host galaxy, reveals that off-nuclear Lyα nebulae have either flat-topped or multipeaked profiles along the extension. All these properties can be understood in terms of superwind activity in the companion galaxy. We also find a diffuse continuum component around the companion, which shows a morphology similar to that of Lyα nebula, and is most likely due to scattering of the quasar light at a dusty halo around the companion. We argue that the superwind could expel dusty material out to the halo region, making a dusty halo for scattering.

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