The Hobby-Eberly Telescope Dark Energy Experiment

Abstract

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 D A (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 ¡ z ¡ 3.8 in 200 square degrees of sky, a volume 10 times that of the Sloan Digital Sky Survey (SDSS) in 100 nights of operation. This survey of large scale structure is sufficient to measure the power spectrum to 2-3% accuracy and constrain the positions of the baryonic acoustical peaks on the matter spectrum to ¢ 1%. This in turn provides sufficient accuracy on H(z) and D A (z) to challenge the level of dark energy constraint expected from the SNAP satellite at a fraction of the cost, while providing unique constraints at z£ 2. The baryonic acoustical peaks method is largely free of systematic biases and provides an independent test of results found by other methods. the constraint, allowing a wide range of possible evolution of the DE equation of state (e.g. [14]). Constraints involving SNe are now approaching the level where systematic uncertainties begin to dominate over random errors [13]. The current generation of experiments (ESSENCE (http://www.ctio.noao.edu/~wsne/), CFHT SNLS [15], and HST observations [2]) will reach the systematics dominated regime, and improved constraints will require the few

A new control system hardware architecture for the Hobby-Eberly Telescope prime focus instrument package

“…The upgrades are motivated largely by the requirements of the HET Dark Energy Experiment (HETDEX), 3,4 but will also support the current suite of instruments plus anticipated future additions.…”

Phase retrieval analysis of the Hobby-Eberly Telescope primary mirror segment figure error and its implication for wavefront sensing for the new wide-field upgrade

“…diameter field of view wide field corrector (WFC), a new tracker and prime focus instrument package (PFIP), and new metrology systems to support the Hobby-Eberly Dark Energy Experiment (HETDEX) [1][2] . The new corrector has improved image quality and a 10 m pupil diameter.…”

Visible Integral-field Replicable Unit Spectrograph (VIRUS) optical tolerance

“…The main science motivation of the VIRUS instrument [1] is to map the evolution of dark energy for the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) [2] , by observing 0.8M Lyman-α emitting galaxies as tracers. In order to achieve this science objective, we are conducting three main engineering/science projects: a major telescope upgrade including replacing the top end of the telescope to allow for a larger focal plane (Wide Field Upgrade) [3] , the construction of the Visual Integral-Field Replicable Unit Spectrograph (VIRUS) instrument, and the execution of a large area (5000 square degrees) blind survey for Lyman-α emitting galaxies at redshifts z < 3.5.…”