A New High-Redshift LymanαEmitter: Possible Superwind Galaxy at z = 5.69

During the course of our deep optical imaging survey for Ly$\alpha$ emitters at $z \approx 5.7$ in the field around the $z=5.74$ quasar SDSSp J104433.04-012502.2, we have found a candidate strong emission-line source. Follow-up optical spectroscopy shows that the emission line profile of this object is asymmetric, showing excess red-wing emission. These properties are consistent with an identification of Ly$\alpha$ emission at a redshift of $z=5.687 \pm 0.002$. The observed broad line width, $\Delta V_{\rm FWHM} \simeq 340$ km s$^{-1}$ and excess red-wing emission also suggest that this object hosts a galactic superwind.