Detection of a Lyman-alpha Emission-Line Companion to the z=4.69 QSO BR1202-0725

We report the detection of a nearby emission-line companion to the z=4.695 quasar BR1202-0725. Deep narrow-band exposures on this field from the UH 2.2 m show a Ly alpha flux of 1.5\times\ten{-16} ergs cm^{-2} s^{-1}. High-resolution HST WFC2 imaging in the F814W filter band shows continuum structure near the emission position, at 2.6" NW of the quasar, corresponding to a projected separation of ~7.5 h^{-1} kpc for \qnought=0.5, where h=\hnought/100\kms Mpc^{-1}. We discuss possible explanations for the combined line and color properties. The ionization is most likely produced by the quasar, but if due to underlying star formation would require a star formation rate of ~7 h^2 solar masses per yr.