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.

We present the first spectroscopic measurements of the [O iii] 5007Å line in two z ∼ 3.1 Lymanalpha emitting galaxies (LAEs) using the new near-infrared instrument LUCIFER1 on the 8.4m Large Binocular Telescope (LBT). We also describe the optical imaging and spectroscopic observations used to identify these Ly-α emitting galaxies. Using the [O iii] line we have measured accurate systemic redshifts for these two galaxies, and discovered a velocity offset between the [O iii] and Ly-α lines in both, with the Ly-α line peaking 342 and 125 km s −1 redward of the systemic velocity. These velocity offsets imply that there are powerful outflows in high-redshift LAEs. They also ease the transmission of Ly-α photons through the interstellar medium and intergalactic medium around the galaxies. By measuring these offsets directly, we can refine both Ly-α-based tests for reionization, and Ly-α luminosity function measurements where the Ly-α forest affects the blue wing of the line. Our work also provides the first direct constraints on the strength of the [O iii] line in high-redshift LAEs. We find [O iii] fluxes of 7 and 36 ×10 −17 erg s −1 cm −2 in two z ∼ 3.1 LAEs. These lines are strong enough to dominate broad-band flux measurements that include the line (in this case, K s band photometry). Spectral energy distribution fits that do not account for the lines would therefore overestimate the 4000Å (and/or Balmer) break strength in such galaxies, and hence also the ages and stellar masses of such high-z galaxies. Subject headings: galaxies: high redshift -intergalactic medium 1 The LBT is an international collaboration among institutions in the United States, Italy and Germany. LBT Corporation partners are: The University of Arizona on behalf of the Arizona university system;

We show that populations of high redshift galaxies grow more luminous as they grow in linear size. This is because the brightness per unit area has a distinct upper limit due to the self-regulating nature of star-formation. As a corollary, we show that the observed increase in characteristic luminosity of Lyman Break Galaxies (L * ) with time can be explained by their increase in size, which scales as H(z) −1 . In contrast, Lyman-α selected galaxies have a characteristic, constant, small size between redshift z = 2.25 and 6.5. Coupled with a characteristic surface brightness, this can explain their non-evolving ultraviolet continuum luminosity function. This compact physical size seems to be a critical determining factor in whether a galaxy will show Lyman-α emission. We base these conclusions on new size measurements for a sample of about 170 Lyman-α selected galaxies with Hubble Space Telescope broad band imaging, over the redshift range 2.25 < z < 6. We combine these with a similar number of Lyman-α selected galaxies with half-light radii from the literature, and derive surface brightnesses for the entire combined sample.

We present post-cryogenic Spitzer imaging at 3.6 and 4.5 µm with the Infrared Array Camera (IRAC) of the Spitzer/HETDEX Exploratory Large-Area (SHELA) survey. SHELA covers ≈24 deg 2 of the Sloan Digital Sky Survey "Stripe 82" region, and falls within the footprints of the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) and the Dark Energy Survey. The HETDEX blind R ∼ 800 spectroscopy will produce ∼ 200,000 redshifts from the Lyman-α emission for galaxies in the range 1.9 < z < 3.5, and an additional ∼ 200,000 redshifts from the [O II] emission for galaxies at z < 0.5. When combined with deep ugriz images from the Dark Energy Camera, K-band images from NEWFIRM, and other ancillary data, the IRAC photometry from Spitzer will enable a broad range of scientific studies of the relationship between structure formation, galaxy stellar mass, halo mass, AGN, and environment over a co-moving volume of ∼0.5 Gpc 3 at 1.9 < z < 3.5. Here, we discuss the properties of the SHELA IRAC dataset, including the data acquisition, reduction, validation, and source catalogs. Our tests show the images and catalogs are 80% (50%) complete to limiting magnitudes of 22.0 (22.6) AB mag in the detection image, which is constructed from the weighted sum of the IRAC 3.6 and 4.5 µm images. The catalogs reach limiting sensitivities of 1.1 µJy at both 3.6 and 4.5 µm (1σ, for R = 2 ′′ circular apertures). As a demonstration of science, we present IRAC number counts, examples of highly temporally variable sources, and galaxy surface density profiles of rich galaxy clusters. In the spirit of Spitzer Exploratory programs we provide all images and catalogs as part of the publication.

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