Las Cumbres Observatory Global Telescope (LCOGT) is a young organization dedicated to time-domain observations at optical and (potentially) near-IR wavelengths. To this end, LCOGT is constructing a world-wide network of telescopes, including the two 2m Faulkes telescopes, as many as 17 x 1m telescopes, and as many as 23 x 40cm telescopes. These telescopes initially will be outfitted for imaging and (excepting the 40cm telescopes) spectroscopy at wavelengths between the atmospheric UV cutoff and the roughly 1-micron limit of silicon detectors. Since the first of LCOGT's 1m telescopes are now being deployed, we lay out here LCOGT's scientific goals and the requirements that these goals place on network architecture and performance, we summarize the network's present and projected level of development, and we describe our expected schedule for completing it. In the bulk of the paper, we describe in detail the technical approaches that we have adopted to attain the desired performance. In particular, we discuss our choices for the number and location of network sites, for the number and sizes of telescopes, for the specifications of the first generation of instruments, for the software that will schedule and control the network's telescopes and reduce and archive its data, and for the structure of the scientific and educational programs for which the network will provide observations.Comment: 59 pages, 9 figures, 4 tables. AAS Latex v5.2. Accepted for publication in Pub. Astr. Soc. Pacifi

We study the escape of Lyα photons from Lyα emitting galaxies (LAEs) and the overall galaxy population using a sample of 99 LAEs at 1.9 < z < 3.8 detected through integral-field spectroscopy of blank fields by the HETDEX Pilot Survey. For 89 LAEs with broad-band counterparts we measure UV luminosities and UV slopes, and estimate E(B − V ) under the assumption of a constant intrinsic UV slope for LAEs. These quantities are used to estimate dust-corrected star formation rates (SF R). Comparison between the observed Lyα luminosity and -2 -that predicted by the dust-corrected SF R yields the Lyα escape fraction. We also measure the Lyα luminosity function and luminosity density (ρ Lyα ) at 2 < z < 4. Using this and other measurements from the literature at 0.3 < z < 7.7 we trace the redshift evolution of ρ Lyα . We compare it to the expectations from the starformation history of the universe and characterize the evolution of the Lyα escape fraction of galaxies. LAEs at 2 < z < 4 selected down to a luminosity limit of L(Lyα) > 3 − 6 × 10 42 erg s −1 (0.25 to 0.5 L * ), have a mean E(B − V ) = 0.13 ± 0.01, implying an attenuation of ∼ 70% in the UV. They show a median UV uncorrected SF R = 11 M ⊙ yr −1 , dust-corrected SF R = 34 M ⊙ yr −1 , and Lyα equivalent widths (EW s) which are consistent with normal stellar populations. We measure a median Lyα escape fraction of 29%, with a large scatter and values ranging from a few percent to 100%. The Lyα escape fraction in LAEs correlates with E(B − V ) in a way that is expected if Lyα photons suffer from similar amounts of dust extinction as UV continuum photons. This result implies that a strong enhancement of the Lyα EW with dust, due to a clumpy multi-phase ISM, is not a common process in LAEs at these redshifts. It also suggests that while in other galaxies Lyα can be preferentially quenched by dust due to its scattering nature, this is not the case in LAEs. We find no evolution in the average dust content and Lyα escape fraction of LAEs from z ∼ 4 to 2. We see hints of a drop in the number density of LAEs from z ∼ 4 to 2 in the redshift distribution and the Lyα luminosity function, although larger samples are required to confirm this. The mean Lyα escape fraction of the overall galaxy population decreases significantly from z ∼ 6 to z ∼ 2. Our results point towards a scenario in which star-forming galaxies build up significant amounts of dust in their ISM between z ∼ 6 and 2, reducing their Lyα escape fraction, with LAE selection preferentially detecting galaxies which have the highest escape fractions given their dust content. The fact that a large escape of Lyα photons is reached by z ∼ 6 implies that better constraints on this quantity at higher redshifts might detect re-ionization in a way that is uncoupled from the effects of dust.

We present a catalog of emission-line galaxies selected solely by their emission-line fluxes using a wide-field integral field spectrograph. This work is partially motivated as a pilot survey for the upcoming Hobby-Eberly Telescope Dark Energy Experiment. We describe the observations, reductions, detections, redshift classifications, line fluxes, and counterpart information for 397 emission-line galaxies detected over 169 with a 3500-5800 Å bandpass under 5 Å full-width-half-maximum (FWHM) spectral resolution. The survey's best sensitivity for unresolved objects under photometric conditions is between 4 and 20 × 10 −17 erg s −1 cm −2 depending on the wavelength, and Lyα luminosities between 3 × 10 42 and 6 × 10 42 erg s −1 are detectable. This survey method complements narrowband and color-selection techniques in the search of high-redshift galaxies with its different selection properties and large volume probed. The four survey fields within the COSMOS, GOODS-N, MUNICS, and XMM-LSS areas are rich with existing, complementary data. We find 105 galaxies via their high-redshift Lyα emission at 1.9 < z < 3.8, and the majority of the remainder objects are low-redshift [O ii]3727 emitters at z < 0.56. The classification between low-and high-redshift objects depends on rest-frame equivalent width (EW), as well as other indicators, where available. Based on matches to X-ray catalogs, the active galactic nuclei fraction among the Lyα emitters is 6%.We also analyze the survey's completeness and contamination properties through simulations. We find five high-z, highly significant, resolved objects with FWHM sizes >44 which appear to be extended Lyα nebulae. We also find three high-z objects with rest-frame Lyα EW above the level believed to be achievable with normal star formation, EW 0 > 240 Å. Future papers will investigate the physical properties of this sample.

We describe the design, construction, and performance of VIRUS-P (Visible Integral-field Replicable Unit Spectrograph -Prototype), the prototype for 150+ identical fiber-fed integral field spectrographs for the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX ‡ ). VIRUS-P was commissioned in 2007, is in regular service on the McDonald Observatory 2.7 m Smith telescope, and offers the largest field of any integral field spectrograph. The 246-fiber IFU uses a densepak-type fiber bundle with a 1/3 fill factor. It is fed at f/3.65 through a telecentric, two-group dioptric focal reducer. The spectrograph's double-Schmidt optical design uses a volume phase holographic grating at the pupil between the articulating f/3.32 folded collimator and the f/1.33 cryogenic prime focus camera. High on-sky throughput is achieved with this catadioptric system by the use of high reflectivity dielectric coatings, which set the 340-670 nm bandwidth. VIRUS-P is gimbal-mounted on the telescope to allow short fibers for high UV throughput, while maintaining high mechanical stability. The instrument software and the 18 square arcmin field, fixed-offset guider provide rapid acquisition, guiding, and precision dithering to fill in the IFU field. Custom software yields Poisson noise limited, sky subtracted spectra. The design characteristics are described that achieved uniformly high image quality with low scattered light and fiber-to-fiber cross talk. System throughput exceeds requirements and peaks at 40%. The observing procedures are described, and example observations are given.

We present unequivocal evidence for a huge (≈80 × 100 × 100 Mpc3) superstructure at redshift z= 0.27 in the three‐dimensional distribution of radio galaxies from the Texas–Oxford NVSS Structure 08h region (TONS08) sample, confirming tentative evidence for such a structure from the 7C redshift survey (7CRS). A second, newly discovered superstructure is also found less securely at redshift 0.35 (of dimensions ≈100 × 100 × 100 Mpc3). We present full observational details on the TONS08 sample which was constructed to probe structures in the redshift range 0 ≲z≲ 0.5 by matching NVSS sources with objects in APM catalogues to obtain a sample of optically bright (E≈R≤ 19.83), radio‐faint (1.4‐GHz flux density S1.4≥ 3 mJy) radio galaxies in the same 25 deg2 area as part II of the 7CRS. Out of the total sample size of 84 radio galaxies, at least 25 are associated with the two ≈100 Mpc‐scale superstructures. We use quasi‐linear structure formation theory to estimate the number of such structures expected in the TONS08 volume if the canonical value for radio galaxy bias is assumed. Under this assumption, the structures represent ≈4–5σ peaks in the primordial density field and their expected number is low (∼10−2–10−4). Because the TONS08 survey was designed to follow up a previously, if tentatively, identified superstructure in the 7CRS, the probability of finding two superstructures in TONS08 is uncertain but, assuming that the tentative detection of the z= 0.35 superstructure is real, must lie between ∼10−4 and ∼10−5, depending on how representative the TONS08 region proves to be. We show that similar structures (with similarly low probabilities) are also found in previous radio galaxy redshift surveys, but their significance has not been fully appreciated because they have been traced by very small numbers of radio galaxies. Fortunately, there are several plausible explanations (many of which are testable) for these low probabilities in the form of potential mechanisms for boosting the bias on large scales. These include the association of radio galaxies with highly biased rich clusters in superstructures, enhanced triggering by group–group mergers and enhanced triggering and/or redshift space distortion in collapsing systems as the growth of superstructures moves into the non‐linear regime.