Abstract
Abstract We describe the survey design, calibration, commissioning, and emission-line detection algorithms for the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX). The goal of HETDEX is to measure the redshifts of over a million Lyα emitting galaxies between 1.88 < z < 3.52, in a 540 deg2 area encompassing a comoving volume of 10.9 Gpc3. No preselection of targets is involved; instead the HETDEX measurements are accomplished via a spectroscopic survey using a suite of wide-field integral field units distributed over the focal plane of the telescope. This survey measures the Hubble expansion parameter and angular diameter distance, with a final expected accuracy of better than 1%. We detail the project’s observational strategy, reduction pipeline, source detection, and catalog generation, and present initial results for science verification in the Cosmological Evolution Survey, Extended Groth Strip, and Great Observatories Origins Deep Survey North fields. We demonstrate that our data reach the required specifications in throughput, astrometric accuracy, flux limit, and object detection, with the end products being a catalog of emission-line sources, their object classifications, and flux-calibrated spectra.
Highlights
Background LightThere is extra light in most detectors that needs to be modeled
Without compelling theoretical guidance or preference for one specific cosmological model compared to any other, we focus Hobby– Eberly Telescope Dark Energy Experiment (HETDEX) on being able to provide a direct measure of the dark energy density for a cosmological constant model
We assume that faint continuum sources may still be hiding within the data. This hypothesis is confirmed via deep HST imaging; for HETDEX the fields with HST overlap, and we find that about 10% of the fibers that made it through the initial continuum cut have faint sources in the HST images
Summary
There is extra light in most detectors that needs to be modeled This background light has contributions from the extended wings of the PSF, scattered light, errors in modeling the wings of the fiber profiles, bias counts not included in the master biases, and controller issues. Because these effects involve a mixture of additive and multiplicative sources, their individual contributions are not modeled, and we do not attempt to measure the relative importance of each component. We rely on an empirical approach that combines all the effects This procedure is not exact, but it allows us to reduce the background subtraction residuals to below a few percent. If one requires background light removed at a level below this, an additional correction is likely needed
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