HETDEX will outfit the 10 m Hobby-Eberly telescope with a new wide field and an array of 145 integral-field spectrographs to survey a 350 sq. degree area in the north galactic cap. Each fiber-coupled spectrograph will cover 350-590 nm, simultaneously at 5 A resolution, providing ~40,000 spectra per exposure. This instrument, called VIRUS, will open up panoramic surveys of the emission-line universe for the first time, and in particular will be used to detect ~1 million Lyman-alpha emitting (LAE) galaxies with 1.9 < z < 3.8 in the survey area. The 3-D map of these galaxies, filling 7.5 cubic Gpc, will be used to detect baryon acoustic oscillations and to constrain the expansion history of the Universe at this early epoch. The measurement will provide a unique opportunity to constrain evolution of dark energy and will provide the most accurate constraint on the curvature of the Universe.

The prototype of the VIRUS unit spectrograph is currently in use for a pilot survey to better measure the properties of LAE galaxies in support of HETDEX.

The HETDEX dataset will also contain ~2 million z<0.5 star-forming galaxies, and many other objects selected spectroscopically, such as metal poor stars.

HETDEX is estimated to cost $34M, of which $20M has been raised. Following the successful Science Requirements Review in June 2007, and the Preliminary design review in early 2008, contracts will be let for the HET wide field upgrade in early 2008. We plan to deploy the upgrade and VIRUS in 2010, and complete observations for HETDEX in 2013.