2003ApJ...591L...9O

We present deep optical spectroscopy of an extended Lyα emission-line blob located in an overdense region at redshift z~3.1 (``blob 1'' of Steidel et al.). The origin of such Lyα blobs has been debated for some time; two of the most plausible models are (1) that it comes from a dust-enshrouded, extreme starburst galaxy with a large-scale galactic outflow (superwind/hyperwind) or (2) that it is the cooling radiation of protogalaxies in dark matter halos. Examination of the kinematic properties of the Lyα emission-line gas should allow us to determine its nature. With this motivation, we performed optical spectroscopy on blob 1 using the Subaru Telescope and found that its kinematic properties can be well explained in terms of superwind activity.