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Full list of authors: Silber, Joseph Harry; Fagrelius, Parker; Fanning, Kevin; Schubnell, Michael; Aguilar, Jessica Nicole; Ahlen, Steven; Ameel, Jon; Ballester, Otger; Baltay, Charles; Bebek, Chris; Beard, Dominic Benton; Besuner, Robert; Cardiel-Sas, Laia; Casas, Ricard; Castander, Francisco Javier; Claybaugh, Todd; Dobson, Carl; Duan, Yutong; Dunlop, Patrick; Edelstein, Jerry; Emmet, William T.; Elliott, Ann; Evatt, Matthew; Gershkovich, Irena; Guy, Julien; Harris, Stu; Heetderks, Henry; Heetderks, Ian; Honscheid, Klaus; Maria Illa, Jose; Jelinsky, Patrick; Jelinsky, Sharon R.; Jimenez, Jorge; Karcher, Armin; Kent, Stephen; Kirkby, David; Kneib, Jean-Paul; Lambert, Andrew; Lampton, Mike; Leitner, Daniela; Levi, Michael; McCauley, Jeremy; Meisner, Aaron; Miller, Timothy N.; Miquel, Ramon; Mundet, Julia; Poppett, Claire; Rabinowitz, David; Reil, Kevin; Roman, David; Schlegel, David; Serrano, Santiago; Van Shourt, William; Sprayberry, David; Tarle, Gregory; Tie, Suk Sien; Weaverdyck, Curtis; Zhang, Kai; Azzaro, Marco; Bailey, Stephen; Becerril, Santiago; Blackwell, Tami; Bouri, Mohamed; Brooks, David; Buckley-Geer, Elizabeth; Penate Castro, Jose; Derwent, Mark; Dey, Arjun; Dhungana, Govinda; Doel, Peter; Eisenstein, Daniel J.; Fahim, Nasib; Garcia-Bellido, Juan; Gaztanaga, Enrique; Gontcho, Satya Gontcho A.; Gutierrez, Gaston; Horler, Philipp; Kehoe, Robert; Kisner, Theodore; Kremin, Anthony; Kronig, Luzius; Landriau, Martin; Le Guillou, Laurent; Martini, Paul; Moustakas, John; Palanque-Delabrouille, Nathalie; Peng, Xiyan; Percival, Will; Prada, Francisco; Allende Prieto, Carlos; Gonzalez de Rivera, Guillermo; Sanchez, Eusebio; Sanchez, Justo; Sharples, Ray; Soares-Santos, Marcelle; Schlafly, Edward; Weaver, Benjamin Alan; Zhou, Zhimin; Zhu, Yaling; Zou, Hu; DESI Collaboration.--This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited., A system of 5020 robotic fiber positioners was installed in 2019 on the Mayall Telescope, at Kitt Peak National Observatory. The robots automatically retarget their optical fibers every 10–20 minutes, each to a precision of several microns, with a reconfiguration time of fewer than 2 minutes. Over the next 5 yr, they will enable the newly constructed Dark Energy Spectroscopic Instrument (DESI) to measure the spectra of 35 million galaxies and quasars. DESI will produce the largest 3D map of the universe to date and measure the expansion history of the cosmos. In addition to the 5020 robotic positioners and optical fibers, DESI's Focal Plane System includes six guide cameras, four wave front cameras, 123 fiducial point sources, and a metrology camera mounted at the primary mirror. The system also includes associated structural, thermal, and electrical systems. In all, it contains over 675,000 individual parts. We discuss the design, construction, quality control, and integration of all these components. We include a summary of the key requirements, the review and acceptance process, on-sky validations of requirements, and lessons learned for future multiobject, fiber-fed spectrographs. © 2022. The Author(s). Published by the American Astronomical Society., The authors in the Barcelona-Madrid Regional Participation Group (BCN-MAD RPG) wish to acknowledge support by MICIN under grants PID2019-111317 GB, PGC2018-094773, PGC2018-102021, SEV-2016-0588, SEV-2016-0597, MDM-2015-0509, and CEX2020-001058-M, some of which include ERDF funds from the European Union. IFAE is partially funded by the CERCA program of the Generalitat de Catalunya. M.A., S.B., N.F., F.P., G.G.R., and J.S. acknowledge support from the Spanish MICINN grants MultiDark CSD2009-00064, IFT-UAM/CSIC Severo Ochoa Award SEV-2012-0249 and AYA2014-60641-C2-1-P, CSIC-AVS contract through MICINN grant AYA2010-21231-C02-01 and CDTI grant IDC-20101033, and support from the Campus of International Excellence UAM+CSIC. This research is supported by the Director, Office of Science, Office of High Energy Physics of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231, and by the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility under the same contract; additional support for DESI is provided by the U.S. National Science Foundation, Division of Astronomical Sciences under Contract No. AST-0950945 to the NSF's National Optical-Infrared Astronomy Research Laboratory; the Science and Technologies Facilities Council of the United Kingdom; the Gordon and Betty Moore Foundation; the Heising-Simons Foundation; the French Alternative Energies and Atomic Energy Commission (CEA); the National Council of Science and Technology of Mexico (CONACYT); the Ministry of Science and Innovation of Spain (MICINN), and by the DESI Member Institutions: https://www.desi.lbl.gov/collaborating-institutions., With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2021-001131-S).

International audience; The Dark Energy Spectroscopic Instrument (DESI) is a Stage IV ground-based dark energy experiment that will measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 square degrees will be measured during the life of the experiment. We describe the installation of the major elements of the instrument at the Mayall 4m telescope, completed in late 2019. The previous prime focus corrector, spider vanes, and upper rings were removed from the Mayall’s Serrurier truss and replaced with the newlyconstructed DESI ring, vanes, cage, hexapod, and optical corrector. The new corrector was optically aligned with the primary mirror using a laser tracker system. The DESI focal plane system was integrated to the corrector, with each of its ten 500-fiber-positioner petal segments installed using custom installation hardware and the laser tracker. Ten DESI spectrographs with 30 cryostats were installed in a newly assembled clean room in the Large Coude Room. The ten cables carrying 5000 optical fibers from the positioners in the focal plane were routed down the telescope through cable wraps at the declination and hour angle axes, and their integral slitheads were integrated with the ten spectrographs. The fiber view camera assembly was installed to the Mayall’s primary mirror cell. Servers for the instrument control system replaced existing computer equipment. The fully integrated instrument has been commissioned and is ready to start its operations phase.

In preparation for the Dark Energy Spectroscopic Instrument (DESI), a new top end was installed on the Mayall 4-meter telescope at Kitt Peak National Observatory. The refurbished telescope and the DESI instrument were successfully commissioned on sky between 2019 October and 2020 March. Here we describe the pointing, tracking and imaging performance of the Mayall telescope equipped with its new DESI prime focus corrector, as measured by six guider cameras sampling the outer edge of DESI's focal plane. Analyzing ~500,000 guider images acquired during commissioning, we find a median delivered image FWHM of 1.1 arcseconds (in the r-band at 650 nm), with the distribution extending to a best-case value of ~0.6 arcseconds. The point spread function is well characterized by a Moffat profile with a power-law index of $\beta$ ~ 3.5 and little dependence of $\beta$ on FWHM. The shape and size of the PSF delivered by the new corrector at a field angle of 1.57 degrees are very similar to those measured with the old Mayall corrector on axis. We also find that the Mayall achieves excellent pointing accuracy (several arcseconds RMS) and minimal open-loop tracking drift (< 1 milliarcsecond per second), improvements on the telecope's pre-DESI performance. In the future, employing DESI's active focus adjustment capabilities will likely further improve the Mayall/DESI delivered image quality., Comment: SPIE Astronomical Telescopes and Instrumentation, 11447-399

The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the universe using the baryon acoustic oscillations technique. The spectra of 35 million galaxies and quasars over 14,000 square degrees will be measured during a 5-year survey. A new prime focus corrector for the Mayall telescope at Kitt Peak National Observatory will deliver light to 5,000 individually targeted fiber-fed robotic positioners. The fibers in turn feed ten broadband multi-object spectrographs. We describe the ProtoDESI experiment, that was installed and commissioned on the 4-m Mayall telescope from August 14 to September 30, 2016. ProtoDESI was an on-sky technology demonstration with the goal to reduce technical risks associated with aligning optical fibers with targets using robotic fiber positioners and maintaining the stability required to operate DESI. The ProtoDESI prime focus instrument, consisting of three fiber positioners, illuminated fiducials, and a guide camera, was installed behind the existing Mosaic corrector on the Mayall telescope. A Fiber View Camera was mounted in the Cassegrain cage of the telescope and provided feedback metrology for positioning the fibers. ProtoDESI also provided a platform for early integration of hardware with the DESI Instrument Control System that controls the subsystems, provides communication with the Telescope Control System, and collects instrument telemetry data. Lacking a spectrograph, ProtoDESI monitored the output of the fibers using a Fiber Photometry Camera mounted on the prime focus instrument. ProtoDESI was successful in acquiring targets with the robotically positioned fibers and demonstrated that the DESI guiding requirements can be met., Comment: Accepted version

The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 square degrees will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. We present an overview of the instrumentation, the main technical requirements and challenges, and the current status of the project. © 2018 SPIE., This research is supported by the Director, Office of Science, Office of High Energy Physics of the U.S. Department of Energy under Contract No. DEAC0205CH1123, and by the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility under the same contract; additional support for DESI is provided by the U.S. National Science Foundation, Division of Astronomical Sciences under Contract No. AST-0950945 to the National Optical Astronomy Observatory; the Science and Technologies Facilities Council of the United Kingdom; the Gordon and Betty Moore Foundation; the Heising-Simons Foundation; the National Council of Science and Technology of Mexico, and by the DESI Member Institutions. The authors are honored to be permitted to conduct astronomical research on Iolkam Du'ag (Kitt Peak), a mountain with particular significance to the Tohono O'odham Nation.

The Dark Energy Spectroscopic Instrument (DESI), currently under construction, is designed to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 40 million galaxies over 14000 sq deg will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. This paper describes the overall design and construction status of the prime focus corrector. The size and complexity of the system poses significant design and production challenges. The optics of the corrector consists of six lenses, ranging from 0.8 - 1.14m in diameter, two of which can be rotated to act as an atmospheric dispersion corrector. These lenses are mounted in custom cells that themselves are mounted in a barrel assembly the alignment of which can be actively controlled by a hexapod system to micrometer precision. The whole assembly will be mounted at the prime focus of the Mayall 4m telescope at Kitt Peak observatory and will be one of the largest lens systems ever built for an optical telescope. Construction of the corrector began in 2014 and is well advanced. The system is due to be delivered to the telescope for installation in early 2018.

The Dark Energy Spectroscopic Instrument (DESI) is under construction and will be used to measure the expansion history of the Universe using the Baryon Acoustic Oscillation (BAO) technique and the growth of structure using redshift-space distortions (RSD). The spectra of 30 million galaxies over 14000 sq deg will be measured over the course of the experiment. In order to provide spectroscopic targets for the DESI survey, we are carrying out a three-band (g,r,z ) imaging survey of the sky using the NOAO 4-m telescopes at Kitt Peak National Observatory (KPNO) and the Cerro Tololo Interamerican Observatory (CTIO). At KPNO, we will use an upgraded version of the Mayall 4m telescope prime focus camera, Mosaic3, to carry out a z-band survey of the Northern Galactic Cap at declinations δ≥+30 degrees. By equipping an existing Dewar with four 4kx4k fully depleted CCDs manufactured by the Lawrence Berkeley National Laboratory (LBNL), we increased the z-band throughput of the system by a factor of 1.6. These devices have the thickest active area fielded at a telescope. The Mosaic3 z-band survey will be complemented by g-band and r-band observations using the Bok telescope and 90 Prime imager on Kitt Peak. We describe the upgrade and performance of the Mosaic3 instrument and the scope of the northern survey.

The Dark Energy Spectroscopic Instrument, to be located at the prime focus of the Mayall telescope, includes a wide field corrector, a 5000 fiber positioner system, and a fiber view camera. The mapping of the sky to the focal plane, needed to position the fibers accurately, is described in detail. A major challenge is dealing with the large amount of distortion introduced by the optics (of order 10% scale change), including time-dependent non-axisymmetric distortions introduced by the atmospheric dispersion compensator. Solutions are presented to measure or mitigate these effects.

The Dark Energy Spectroscopic Instrument (DESI), which is currently under construction, is designed to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 40 million galaxies over 14000 sq deg will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fibre optic positioners. The fibres in turn feed ten broad-band spectrographs. The prime focus corrector for DESI consists of six lenses that range in diameter from 0.80 - 1.14 meters and from 83 - 237 kg in weight. The alignment of the large lenses of the optical corrector poses a significant challenge as in order to meet the fibre throughput requirements they have to be aligned to within a tolerance of ~50 micrometres. This paper details the design for the cells that will hold the lenses and the alignment and assembly procedure for the mounting of the lenses into the cells and into the complete barrel assembly. This is based on the experience obtained from the alignment of the Dark Energy Camera (DECam) instrument which was successfully assembled and aligned by the same team and we include in the paper the lessons learnt and design modifications that will be implemented on the DESI system.

Motivated by a desire to improve the KPNO Mayall 4m telescope’s pointing and tracking performance prior to the start of the DESI installation and by a need to improve the maintainability of its telescope control system (TCS), we recently completed a major modernization of that system based heavily on recent changes made at the CTIO Blanco 4m, as described by Warner et al (2012). We describe here the things we did differently from the Blanco upgrade. We also present results from the as-built performance of the new servo and pointing systems.

The Dark Energy Spectroscopic Instrument (DESI) is under construction for installation on the Mayall 4 Meter telescope. The use of a liquid cooling system is proposed to maintain the DESI prime focus assembly temperature within ±1°C of ambient. Due to concerns of fluid deposition onto optical surfaces from possible leaks, systematic tests were performed of the effects on first surface aluminized mirrors of ethylene glycol and two other candidate coolants. Objective measurement of scattering and reflectivity was an important supplement to visual inspection. Rapid cleanup of a coolant spill followed by a hand wash of the mirror limited surface degradation to the equivalent of a few months of general environmental exposure. Prolonged exposure to corrosive coolants dissolved the aluminum, necesitating mirror recoating.

The Mayall 4-meter telescope recently went through a major modernization of its telescope control system in preparation for DESI. We describe MPK (Mayall Pointing Kernel), our new software for telescope control. MPK outputs a 20Hz position-based trajectory with a velocity component, which feeds into Mayall’s new servo system over a socket. We wrote a simple yet realistic servo simulator that let us develop MPK mostly without access to real hardware, and also lets us provide other teams with a Mayall simulator as test bed for development of new instruments. MPK has a small core comprised of prioritized, soft real-time threads. Access to the core’s services is via MPK’s main thread, a complete, interactive Tcl/Tk shell, which gives us the power and flexibility of a scripting language to add any other features, from GUIs, to modules for interaction with critical subsystems like dome or guider, to an API for networked clients of a new instrument (e.g., DESI). MPK is designed for long term maintainability: it runs on a stock computer and Linux OS, and uses only standard, open source libraries, except for commercial software that comes with source code in ANSI C/C++. We discuss the technical details of how MPK combines the Reflexxes motion library with the TCSpk/TPK pointing library to generically handle any motion requests, from slews to offsets to sidereal or non-sidereal tracking. We show how MPK calculates when the servos have reached a steady state. We also discuss our TPOINT modeling strategy and report performance results.

The Dark Energy Spectroscopic instrument (DESI) is a 5000 fiber multi-object spectrometer system under development for installation on the National Optical Astronomy Observatory (NOAO) Kitt Peak 4m telescope (the Mayall telescope). DESI is designed to perform a 14,000° (square) galaxy and Quasi-Stellar Object (QSO) redshift survey to improve estimates of the dark energy equation of state. The survey design imposes numerous constraints on a prime focus corrector design, including field of view, geometrical blur, stability, fiber injection efficiency, zenith angle, mass and cost. The DESI baseline wide-field optical design described herein provides a 3.2° diameter field of view with six 0.8- 1.14m diameter lenses and an integral atmospheric dispersion compensator.

The KPNO Nicholas U. Mayall 4-meter telescope is to be the host facility for the Dark Energy Spectroscopic Instrument (DESI). DESI will record broadband spectra simultaneously for 5000 objects distributed over a 3-degree diameter field of view; it will record the spectra of approximately 20 million galaxies and quasi-stellar objects during a five-year survey. This survey will improve the combined precision of measurement on the dark energy equation of state today (w 0 ) and its evolution with redshift (w a ) by approximately a factor of ten over existing spectroscopy baryon acoustic oscillation surveys (e.g., BOSS 1 ) in both co-moving volume surveyed and number of galaxies mapped. Installation of DESI on the telescope is a complex procedure, involving a complete replacement of the telescope top end, routing of massive fiber cables, and installation of banks of spectrographs in an environmentally-controlled lab area within the dome. Furthermore, assembly of the instrument and major subsystems must be carried out on-site given their size and complexity. A detailed installation plan is being developed early in the project in order to ensure that DESI and its subsystems are designed so they can be safely and efficiently installed, and to ensure that all telescope and facility modifications required to enable installation are identified and completed in time.

TripleSpec 4 (TS4) is a near-infrared (0.8um to 2.45um) moderate resolution (R ~ 3200) cross-dispersed spectrograph for the 4m Blanco Telescope that simultaneously measures the Y, J, H and K bands for objects reimaged within its slit. TS4 is being built by Cornell University and NOAO with scheduled commissioning in 2015. TS4 is a near replica of the previous TripleSpec designs for Apache Point Observatory's ARC 3.5m, Palomar 5m and Keck 10m telescopes, but includes adjustments and improvements to the slit, fore-optics, coatings and the detector. We discuss the changes to the TripleSpec design as well as the fabrication status and expected sensitivity of TS4.

We describe the design, construction and measured performance of the Kitt Peak Ohio State Multi-Object Spectrograph (KOSMOS) for the 4-m Mayall telescope and the Cerro Tololo Ohio State Multi-Object Spectrograph (COSMOS) for the 4-m Blanco telescope. These nearly identical imaging spectrographs are modified versions of the OSMOS instrument; they provide a pair of new, high-efficiency instruments to the NOAO user community. KOSMOS and COSMOS may be used for imaging, long-slit, and multi-slit spectroscopy over a 100 square arcminute field of view with a pixel scale of 0.29 arcseconds. Each contains two VPH grisms that provide R~2500 with a one arcsecond slit and their wavelengths of peak diffraction efficiency are approximately 510nm and 750nm. Both may also be used with either a thin, blue-optimized CCD from e2v or a thick, fully depleted, red-optimized CCD from LBNL. These instruments were developed in response to the ReSTAR process. KOSMOS was commissioned in 2013B and COSMOS was commissioned in 2014A., SPIE 2014 Astronomical Telescopes + Instrumentation, Proc. SPIE 9147-34

We measure the z=0 B-band optical luminosity function (LF) for galaxies selected in a blind HI survey. The total LF of the HI selected sample is flat, with Schechter parameters M*=-19.38_{-0.62}^{+1.02} + 5 log h mag and alpha=-1.03_{-0.15}^{+0.25}, in good agreement with LFs of optically selected late-type galaxies. Bivariate distribution functions of several galaxy parameters show that the HI density in the local Universe is more widely spread over galaxies of different size, central surface brightness, and luminosity than is the optical luminosity density. The number density of very low surface brightness (>24.0 mag/arcsec^2) gas-rich galaxies is considerably lower than that found in optical surveys designed to detect dim galaxies. This suggests that only a part of the population of LSB galaxies is gas rich and that the rest must be gas poor. However, we show that this gas-poor population must be cosmologically insignificant in baryon content. The contribution of gas-rich LSB galaxies (>23.0 mag/arcsec^2) to the local cosmological gas and luminosity density is modest (18_{-5}^{+6} and 5_{-2}^{+2} per cent respectively); their contribution to Omega_matter is not well-determined, but probably < 11 per cent. These values are in excellent agreement with the low redshift results from the Hubble Deep Field., Accepted for publication in MNRAS, 12 pages 6 figures

Using optical spectra of the nuclei of 250 galaxies chosen from the Automated Plate Measuring Facility (APM) survey of UK Schmidt plates, we derive synthetic B-V and V-R colors, estimates of reddening from Balmer decrements, metallicity via oxygen abundance, and star formation rate from the Hα luminosity. We also present mass-to-light ratios and gas mass fractions from 21 cm H I measurements of 238 APM survey galaxies, 101 of which also have optical spectra. This sample of galaxies spans a large range in surface brightness, from high surface brightness irregular galaxies down to the kind of low surface brightness (LSB) galaxies that are missing from most magnitude-limited catalogs. The generally blue global colors are best explained by a combination of low metallicity and active star formation, primarily because of the tremendous scatter in metallicity versus B-V. Optical spectra show the presence of G and K main-sequence stars in the nuclei of these galaxies, and the stellar mass-to-light ratios and gas mass fractions show the galaxies as a whole to be gas-rich. LSB galaxies are most likely to experience sporadic low levels of star formation over gigayear timescales.

We present flux-calibrated spectra in the range 3500 to 8000 A for the nuclear regions of 250 galaxies and H I 21 cm line profiles for 238 galaxies selected from the catalog of low surface brightness galaxies identified in Automated Plate Measuring Facility (APM) scans of UK Schmidt Telescope survey plates. For the optical spectra, common nebular absorption- and emission-line equivalent widths and emission-line fluxes were measured with typical errors of about 20%. H I mass and velocity widths were measured from the 21 cm line emission, with 15% accuracy. Galaxies in this study span over 6 mag in surface brightness. Only about 20% of these galaxies show spectroscopic evidence of active galactic nuclei. Derived quantities such as synthetic colors, metallicity, star formation rate, the ratio of neutral hydrogen mass to blue light, and gas mass fraction are presented in a companion paper.

The HI mass function (HIMF) for galaxies in the local universe is constructed from the results of the Arecibo HI Strip Survey, a blind extragalactic survey in the 21cm line. The survey consists of two strips covering in total 65 square degrees of sky, with a depth of cz = 7400 km/s and was optimized to detect column densities of neutral gas N_HI > 10^18 cm^-2 (5 sigma). The survey yielded 66 significant extragalactic signals of which approximately 50% are cataloged galaxies. No free floating HI clouds without stars are found. VLA follow-up observations of all signals have been used to obtain better measurements of the positions and fluxes and allow an alternate determination of the achieved survey sensitivity. The resulting HIMF has a shallow faint end slope (alpha ~ 1.2), and is consistent with earlier estimates computed for the population of optically selected gas rich galaxies. This implies that there is not a large population of gas rich low luminosity or low surface brightness galaxies that has gone unnoticed by optical surveys. The cosmological mass density of HI at the present time determined from the survey, Omega_HI = (2.0 +/- 0.5) x 10^-4, is in good agreement with earlier estimates. We determine lower limits to the average column densities of the galaxies detected in the survey and find that none of the galaxies have below 10^19.7 cm^-2, although there are no observational selection criteria against finding lower density systems.

The High-Resolution Near-InfraRed Spectrograph (HRNIRS) concept for the Gemini telescopes combines a seeing limited R ~ 70000 cross-dispersed mode and an MCAO-fed near diffraction-limited R ~ 30000 multi-object mode into a single compact instrument operating over the 1 - 5 μm range. The HRNIRS concept was developed in response to proposals issued through the Aspen instrument process by Gemini. Here we review the science drivers and key functional requirements. We present a general overview of the instrument and estimate the limiting performance.

HRNIRS is an extremely versatile high-resolution infrared facility spectrograph designed for the Gemini South telescope. Operating over the 1.05 - 5.5 micron wavelength range, it has the capability to carry out a wide range of scientific programs by incorporating two separate modes of operation. The first is a conventional single slit cross-dispersed mode providing spectral resolution R ~ 70000 with a 0.4 arcsec slit over as much as an octave in wavelength, thus covering most of the JHK or LM windows in a single observation. In this mode the spectrograph accepts the Gemini seeing-limited f/16 input over a small field. A built-in modulator and polarizer allow HRNIRS to measure both linear and circular polarization. The second mode is a moderately-high resolution (R ~ 30000) spectrograph observing multiple objects simultaneously within a 2 arcmin field fed by the f/33.2 Gemini MCAO beam. In this paper, we discuss the optical design considerations, present the resulting design and show that the predicted performance meets the design requirements.

The High-resolution Near-infrared Spectrograph (HRNIRS) concept for the Gemini telescopes combines a seeing-limited R ~ 7000 cross-dispersed mode and an MCAO-fed near diffraction-limited R ~ 20000 multi-object mode into a single compact instrument operating over the 0.9 - 5.5 μm range. We describe the systems engineering and performance modeling aspects of this study, emphasizing simulations of high-precision radial verlocity measurements in the Gemini Cassegrain-focus instrument environment.

The High-resolution Near-infrared Spectrograph (HRNIRS) concept for the Gemini telescopes combines a seeing-limited R ~ 70000 cross-dispersed mode and a MCAO-fed near diffraction-limited R ~ 20000 multi-object mode into a single compact instrument operating over the 0.9-5.5μm range. We describe the mechanical design, emphasizing the challenging design requirements and how they were met. The approach of developing the optical and mechanical designs in concert and utilizing proven working concepts from the Gemini Near Infra-Red Spectrograph were key elements of the design philosophy. Liang, et al. provides a detailed discussion of the optical design, Hinkle, et al. describes the science cases and requirements as well as a general overview, and Eikenberry, et al. describes the systems engineering and performance aspects of HRNIRS.

We present the design for a recently approved instrument for the Keck Telescope. Called OSIRIS, it was inspired by the optical spectrograph TIGER of R. Bacon et al. and will utilize an infrared transmissive lenslet array to sample a rectangular field of view at close to the Keck diffraction limit. By packing the spectra very closely together (2 pixel rows per spectrum) and using the Rockwell Hawaii-2 detector (wavelengths between 1 and 2.5 microns), we will achieve a relatively large field of view (up to 6."4) while maintaining full broad-band spectral coverage at a resolution of 3900. Due to the extremely low backgrounds between night sky lines and at AO spatial samplings, the instrument will reach point source sensitivities several times fainter than any existing infrared spectrograph. We are also coupling a separate infrared AO camera dubbed SHARC to work as an acquisition camera and to monitor the point spread function's behavior during long spectroscopic exposures. Among the challenges of the instrument are: a fully cryogenic design, four spatial resolutions from 0."02 to 0."10, large aluminum optics for the spectrography, extremely repeatable spectral formats and a sophisticated data reduction pipeline.

The Keck II Adaptive Optics system and the NIRC2 camera provide a unique facility for high angular resolution imaging and spectroscopy in the near infrared. In this paper, we present the result of a unique project to map the entire surface of Io in the thermal infrared (Lp band centered at 3.8 μm). This project was undertaken by a team from the W. M. Keck Observatory and UC Berkeley to illustrate the power of this instrumentation. The 75-milliarcsec-resolution images, corresponding to ~200 km of linear spatial resolution on Io, have been combined to build a thermal infrared map of the entire satellite. We have identified 26 hot spots including one that was undetected by the Galileo mission. A movie and a Java applet featuring a volcanically active rotating satellite were created.

Results from the Arecibo HI Strip Survey, an unbiased extragalactic HI survey, combined with optical and 21cm follow-up observations, determine the HI Mass Function and the cosmological mass density of HI at the present epoch. Both are consistent with earlier estimates, computed for the population of optically selected galaxies. This consistency occurs because, although the distribution of optical central surface brightnesses among galaxies is flat, we fail to find a population of galaxies with central surface brightnesses fainter than 24 B-mag/arcsec^2, even though there is no observational selection against them., Comment: 5 pages, including 3 encapsulated postscript figures. Presented at the workshop `HI in the Local Universe', Sydney, May 13-15 1996. Accepted for publication by PASA. Also available from http://www.atnf.csiro.au/Publications/HI_workshop/proceedings.html

We have developed a catalog of local low surface brightness galaxies (LSBGs) which is selected by objective criteria. We present here a luminosity function (LF) for LSBGs based on that catalog. This LF includes the effects of the completeness corrections to the LSBG catalog, and includes only galaxies with surface brightnesses (22.25 ≤ μB(0) ≤ 24.5) fainter than those included in the CfA Redshift Survey (see Marzke et al. 1994, AJ 108, 437). The best-fitting Schechter function has parameters \(\alpha = -1.42, M_B^* = -18.34\), and \(\phi^* = 0.0036 \ h^3 \ \textup{Mpc}^{-3} \ \textup{mag}^{-1}\). Thus, surveys which do not take account of the observational selection bias imposed by surface brightness are missing a substantial fraction of the local galaxies, but, this missed fraction is not large enough to explain the counts of faint blue galaxies observed at moderate redshift.

We report the discovery of a third very large, gas-rich low surface brightness (LSB) disk galaxy, which we designate 1226+0105. Its equatorial coordinates are α=12 h 26 m 39 s .2 and δ=1°05'38″ (1950), and it is at a redshift of 23,660 km s −1 . It exhibits a number of similarities to the previous described examples of this class, Malin 1 (Bothun et al. 1987; Impey & Bothun 1989) and F568-6 (Bothun et al. 1990), in that it has a large total H I mass of ∼2×10 10 M ○. , a long disk scale length of ∼14 kpc, a high total luminosity of M B =−21.6, and it harbors an active nucleus. It also shows some striking differences from the previous two

We use a sample of about 340 low surface brightness (LSB) disk galaxies with measured redshifts in combination with the Center for Astrophysics redshift survey to test the hypothesis that LSB galaxies have a deficit of nearby companion galaxies compared to high surface brightness (HSB) disk galaxies. We find a very strong statistical deficit of galaxies located within a projected radius of 0.5 Mpc and within a velocity of 500 km/s around LSB disk galaxies compared to HSB ones. Further, comparing LSB and HSB disk galaxies which are located in the same portion of the sky indicates that the average distance to the nearest neighbor is 1.7 times farther for LSB disk galaxies. A Komologorov-Smirnoff test rules out, at greater than the 99 percent confidence level, the hypothesis that the distribution of nearest-neighbor distances is the same for HSB and LSB disk galaxies. We speculate that LSB disk galaxies have relatively long formation time scales and therefore must form in relative isolation. In addition, the lack of tidal interactions over a Hubble time serves to suppress the overall star-formation rate as no external trigger is available to help clump the gas. The observed low surface densities of H I in combination with the low probability of tidal interactions effectively prevents these disk galaxies from evolving very rapidly.

Recently, Weymann et al. (1991, ApJ, 373) presented composite spectra of broad absorption line (BAL) QSOs as divided into two classes, those with spectra containing absorption from both high and low-ionization ionic species, and those showing only high-ionization absorption troughs. They showed that the spectral properties of the former class differed from those of the latter (and non-broad absorption line QSOs) in that their spectra contain stronger emission from Fe II and possibly Fe III, their continua are substantially redder, and Lyman α and N V emission lines are weaker. Here, it is shown that correction for the extinction of a modest amount of dust can bring the spectra into coincidence