The Hobby-Eberly Telescope Dark Energy Experiment

We describe a project (HETDEX) to measure the evolution of dark energy out to z∼4 with high precision. The galaxy power spectrum contains the baryonic oscillations seen in the CMB, and these features remain in the linear regime at high redshift. The separation of these peaks in the power spectrum is a standard ruler imprinted on both the angular and redshift space distribution of galaxies, providing direct constraints on the local Hubble constant H(z) and the angular diameter distance DA(z), both of which are related to the dark energy equation of state parameter w(z).We propose the use of Ly‐α emitting galaxies as the tracer of the power spectrum, and describe the Visible IFU Replicable Ultra‐cheap Spectrograph (VIRUS), capable of undertaking such a survey. VIRUS will be a very wide field integral field spectrograph of a new replicated design, consisting of more than a hundred individual spectrograph units. The VIRUS instrument mounted on a new wide field corrector on the Hobby‐Eberly Telescope (HET) will allow 1 million Ly‐α emitting galaxies to be mapped over 1.8 2. The baryonic acoustical peaks method is largely free of systematic biases and provides an independent test of results found by other methods.