[Show abstract][Hide abstract] ABSTRACT: 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 × 1042 and 6 × 1042 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, EW0>240 Å. Future papers will investigate the physical properties of this sample.
The Astrophysical Journal Supplement Series 12/2010; 192(1):5. · 16.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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 (HETDEX). We describe the observations, reductions, detections, redshift classifications, line fluxes, and counterpart information for 397 emission-line galaxies detected over 169 sq.arcmin with a 3500-5800 Ang. bandpass under 5 Ang. full-width-half-maximum (FWHM) spectral resolution. The survey's best sensitivity for unresolved objects under photometric conditions is between 4-20 E-17 erg/s/sq.cm depending on the wavelength, and Ly-alpha luminosities between 3-6 E42 erg/s are detectable. This survey method complements narrowband and color-selection techniques in the search for 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 104 galaxies via their high redshift Ly-alpha emission at 1.9<z<3.8, and the majority of the remainder objects are low redshift [OII]3727 emitters at z<0.56. The classification between low and high redshift objects depends on rest frame equivalent width, as well as other indicators, where available. Based on matches to X-ray catalogs, the active galactic nuclei (AGN) fraction amongst the Ly-alpha emitters (LAEs) is 6%. We also analyze the survey's completeness and contamination properties through simulations. We find five high-z, highly-significant, resolved objects with full-width-half-maximum sizes >44 sq.arcsec which appear to be extended Ly-alpha nebulae. We also find three high-z objects with rest frame Ly-alpha equivalent widths above the level believed to be achievable with normal star formation, EW(rest)>240 Ang. Comment: 45 pages, 36 figures, 5 tables, submitted to ApJS
[Show abstract][Hide abstract] ABSTRACT: We study the escape of Ly-alpha photons from Ly-alpha 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 showing counterparts in deep broad-band images we
measure the rest-frame UV luminosity and the UV slope, which we use to estimate
E(B-V) under the assumption of a constant intrinsic UV slope for LAEs. These
two quantities are used to measure the dust-corrected star formation rate
(SFR). A comparison between the observed Ly-alpha luminosity and that predicted
by the dust-corrected SFR yields the Ly-alpha escape fraction. We also measure
the Ly-alpha luminosity function. Integration of the luminosity function
provides a measurement of the Ly-alpha luminosity density across our redshift
range. We combine our data with that from other surveys at 0.3<z<7.7 to trace
the evolution of the Ly-alpha luminosity density. We then compare it to that
expected from the star-formation history of the universe in order to
characterize the evolution of the Ly-alpha escape fraction of the overall
galaxy population [abriged]
[Show abstract][Hide abstract] ABSTRACT: We present the design and performance of the prototype Visible Integral-field Replicable Unit Spectrograph (VIRUS-P) camera. Commissioned in 2007, VIRUS-P is the prototype for 150+ identical fiber-fed integral field spectrographs for the Hobby-Eberly Telescope Dark Energy Experiment. With minimal complexity, the gimbal mounted, double-Schmidt design achieves high on-sky throughput, image quality, contrast, and stability with novel optics, coatings, baffling, and minimization of obscuration. The system corrector working for both the collimator and f / 1.33 vacuum Schmidt camera serves as the cryostat window while a 49 mm square aspheric field flattener sets the central obscuration. The mount, electronics, and cooling of the 2k × 2k, Fairchild Imaging CCD3041-BI fit in the field-flattener footprint. Ultra-black knife edge baffles at the corrector, spider, and adjustable mirror, and a detector mask, match the optical footprints at each location and help maximize the 94% contrast between 245 spectra. An optimally stiff and light symmetric four vane stainless steel spider supports the CCD which is thermally isolated with an equally stiff Ultem-1000 structure. The detector/field flattener spacing is maintained to 1 mum for all camera orientations and repeatably reassembled to 12 mum. Invar rods in tension hold the camera focus to +/-4 mum over a -5-25 °C temperature range. Delivering a read noise of 4.2 e- RMS, sCTE of 1-10-5 , and pCTE of 1-10-6 at 100 kpix/s, the McDonald V2 controller also helps to achieve a 38 hr hold time with 3 L of LN2 while maintaining the detector temperature setpoint to 150 muK (5sigma RMS).
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: Low-dispersion optical spectra have been obtained with the Hobby-Eberly Telescope of 22 very red objects found in early imaging data from the Sloan Digital Sky Survey (SDSS). The objects are assigned spectral types on the Two Micron All Sky Survey (2MASS) system and are found to range from late M to late L. The red and near-infrared colors from SDSS and 2MASS correlate closely with each other, and most of the colors are closely related to spectral type in this range; the exception is the i*-z* color, which appears to be independent of spectral type between about M7 and L4. The spectra suggest that this independence is due to the disappearance of the TiO and VO absorption in the i band for later spectral types, the presence of strong Na I and K I absorption in the i band, and the gradual disappearance of the 8400 Å absorption of TiO and FeH in the z band.
The Astronomical Journal 12/2007; 123(1):458. · 4.97 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) will outfit
the 10 m HET with a new wide field and an array of 145 integral-field
spectrographs to survey a 400 sq. degree area in the north galactic cap.
Each fiber-coupled unit spectrograph will cover 350-590 nm,
simultaneously at 5 A resolution, providing 40,000 spectra per
exposure. This instrument, called VIRUS, will open up surveys of the
emission-line universe for the first time, and in particular will be
used to detect 1 million Lyman-alpha emitting (LAE) galaxies with 1.9
< z < 3.8.
The prototype of the VIRUS unit spectrograph (VIRUS-P) is a powerful
instrument in its own right. Used on the McDonald 2.7 m Smith reflector,
it covers the largest area of any integral field spectrograph, and has
coverage down to 340 nm. It is currently in use for a pilot survey to
better measure the properties of LAE galaxies in support of HETDEX,
among other investigations where it is uniquely powerful. We report
details of the VIRUS-P design and its performance.
VIRUS-P has been made possible by a generous donation from the Cynthia
and George Mitchell Foundation. This work is supported by Texas Advanced
Research Program Grant No. 003658-0005-2006
[Show abstract][Hide abstract] ABSTRACT: We present the design of, and the science drivers for, the Visible Integral-field Replicable Unit Spectrograph (VIRUS). This instrument is made up of 145 individually small and simple spectrographs, each fed by a fiber integral field unit. The total VIRUS-145 instrument covers ~30 sq. arcminutes per observation, providing integral field spectroscopy from 340 to 570 nm, simultaneously, of 35,670 spatial elements, each 1 sq. arcsecond on the sky. This corresponds to 15 million resolution elements per exposure. VIRUS-145 will be mounted on the Hobby-Eberly Telescope and fed by a new wide-field corrector with 22 arcminutes diameter field of view. VIRUS represents a new approach to spectrograph design, offering the science multiplex advantage of huge sky coverage for an integral field spectrograph, coupled with the engineering multiplex advantage of >100 spectrographs making up a whole. VIRUS is designed for the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) which will use baryonic acoustic oscillations imprinted on the large-scale distribution of Lyman-α emitting galaxies to provide unique constraints on the expansion history of the universe that can constrain the properties of dark energy.
[Show abstract][Hide abstract] ABSTRACT: Optical spectra were obtained during the period 2000 October-2003 May on the 2.6-m Nordic Optical Telescope (NOT) using the Andalucia faint object spectrograph, the 4.2-m William Herschel telescope (WHT) using ISIS, the 2.7-m Smith reflector at McDonald with the Imaging Grism Instrument (IGI), and the Hobby-Eberly Telescope (HET) using the Marcario low-resolution spectrograph (LRS). (3 data files).
[Show abstract][Hide abstract] ABSTRACT: We present a clustering analysis of the Texas–Oxford NVSS Structure (TONS) radio galaxy redshift survey. This complete flux-limited survey consists of 268 radio galaxies with spectroscopic redshifts in three separate regions of the sky covering a total of 165 deg2. By going to faint radio flux densities (s1.4≥ 3 mJy) but imposing relatively bright optical limits (E≈R≈ 19.5), the TONS sample is optimized for looking at the clustering properties of low-luminosity radio galaxies in a region of moderate (0 ≲z≲ 0.5) redshifts. We use the two-point correlation function to determine the clustering strength of the combined TONS08 and TONS12 subsamples and find a clustering strength of r0(z) = 8.7 ± 1.6 Mpc (h= 0.7). If we assume growth of structure by linear theory and that the median redshift is 0.3, this corresponds to r0(0) = 11.0 ± 2.0 Mpc, which is consistent with the clustering strength of the underlying host galaxies (∼2.5 L★ ellipticals) of the TONS radio galaxy population.
Monthly Notices of the Royal Astronomical Society 02/2005; 357(4):1231 - 1254. · 5.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present a clustering analysis of the Texas-Oxford NVSS Structure (TONS) radio galaxy redshift survey. This complete flux-limited survey consists of 268 radio galaxies with spectroscopic redshifts in three separate regions of the sky covering a total of 165 deg^2. By going to faint radio flux densities (s_1.4>3 mJy) but imposing relatively bright optical limits (E R 19.5), the TONS sample is optimised for looking at the clustering properties of low luminosity radio galaxies in a region of moderate (0 < z < 0.5) redshifts. We use the two point correlation function to determine the clustering strength of the combined TONS08 and TONS12 sub-samples and find a clustering strength of r_0(z)=8.7+/-1.6 Mpc (h=0.7). If we assume growth of structure by linear theory and that the median redshift is 0.3, this corresponds to r_0(0)=11.0+/-2.0 Mpc which is consistent with the clustering strength of the underlying host galaxies (~ 2.5 Lstar ellipticals) of the TONS radio galaxy population. Comment: 18 pages, MNRAS accepted. Full paper including all spectra can be found at http://www.noao.edu/noao/staff/brand/brand_corr_fn.ps.gz
[Show abstract][Hide abstract] ABSTRACT: LRS-J is a 142 mm f / 1 near infrared (J-Band) camera designed as a drop in replacement for the optical camera installed on the Hobby--Eberly Telescope (HET) multi-object low resolution spectrograph (LRS). The Hawaii-1RG (H1RG) based instrument is liquid nitrogen cooled, but it mates to the warm LRS making use of the existing longslit and multi-object (MOS) units as well as the existing optical collimator. LRS-J utilizes a molecular beam epitaxy (MBE) based Hawaii-1RG (H1RG) detector. The design is a fully cryogenic catadioptric Maksutov-type, with the detector at the internal focus. This configuration produces excellent images, but presents particular challenges in the mounting of the detector. This is the first time that such an arrangement has been used in an astronomical instrument with an infrared detector. By replacing the conventional optical grisms with two 170 mm diameter near-IR VPH grisms, LRS-J covers the 0.9-1.3 mum bandpass with R ~ 1750-2000. We present the opto-mechanical design of LRS-J including the thermally self-compensating corrector doublet mount, and 100 mum/turn cryogenic mirror adjusters, FEA optimized vacuum housing, and custom Dewar. We also characterize the electrical and thermal connections necessary to mount the detector head in this unusually small inverted arrangement.
[Show abstract][Hide abstract] ABSTRACT: The TONS08 survey is in one of the areas covered by the 7CRS (Willott et al., 2002MNRAS.335.1120W) and the TexOx-1000 (TOOT) survey (Hill & Rawlings, 2002, ASP Conf. Proc., Leiden. Astron. Soc. Pac., San Francisco). It covers the region 08h 10m 20s
[Show abstract][Hide abstract] ABSTRACT: The first second-generation instrument for the Hobby-Eberly telescope is a novel J band camera (LRS-J) which mates to the existing low resolution spectrograph (LRS). This camera uses the existing LRS longslit and mutltiobject units as well as the LRS five element collimator but uses its own J optimized volume holographic grisms, f/1 cryogenically cooled camera, and readout electronics built around a Rockwell HAWAII-1 array. We minimized the development time of the controller by reusing as much of the existing framework as possible. The modular design of the existing LRS CCD controller allows us to modify only the clock-driver and penthouse (pre-amplifier) modules. Furthermore, we were able to use existing multilayer circuit boards already fabricated for these two modules. Thus, the LRS-J controller required only the substitution of components on two modules and the design of a new header (dewar) board to fit the HAWAII-1 socket. With these modifications, based on its perfomance with CCDs, we predict a noise and crosstalk performance at the most competitive level.
[Show abstract][Hide abstract] ABSTRACT: Highly efficient Volume phase holographic (VPH) gratings do not lend
themselves to use in existing spectrographs except for grism
spectrographs where VPH grisms can be designed that disperse but do not
deviate the light. We discuss our program to outfit existing
spectrographs [the Imaging grism instrument (IGI) on the McDonald
Observatory Smith Reflector, and the Hobby-Eberly Telescope Marcario Low
Resolution Spectrograph (LRS)] with efficient VPH grisms. We present
test data on sample gratings from Ralcon Development Lab, and compare
them to theoretical predictions. We have created a simple test bench for
efficiency measurements of VPH gratings, which we describe. Finally we
present first results from the use of VPH grisms in IGI and the LRS, the
latter being the largest grism ever deployed in an astronomical
spectrograph. We also look forward to using VPH grisms in the LRS
infrared extension, which covers the wavelength range from 0.9 to 1.3
[Show abstract][Hide abstract] ABSTRACT: The Hobby-Eberly Telescope (HET) imposes unique constraints on the design of a spectral calibration system. Its 9.2 m aperture and queue scheduled operation make traditional dome screens impractical. Furthermore, the changing pupil of the HET's tilted Aricebo design is far more drastic than the simple rotation of traditional alt-azimuth telescopes. Given these constraints we elected to build an internal spectral calibration system (SCS) common to all instruments. The SCS can feed all HET instruments from a uniformly illuminated Lambertian screen located within the spherical abberation corrector (SAC) at the telescope's second pupil. A moving baffle installed at the third pupil will reproduce, during calibration, the actual HET pupil seen in a science exposure. We eliminated all heat sources at the SAC by locating the lamps in the basement below the telescope and coupling source to screen through 12 600 mum diameter 35 m long fibers.