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

Abstract

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.

Based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.