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  • 1
    Online Resource
    Online Resource
    Target Selection and Validation of DESI Quasars
    American Astronomical Society ; 2023
    In:  The Astrophysical Journal Vol. 944, No. 1 ( 2023-02-01), p. 107-
    Details
    In: The Astrophysical Journal, American Astronomical Society, Vol. 944, No. 1 ( 2023-02-01), p. 107-
    Abstract: The Dark Energy Spectroscopic Instrument (DESI) survey will measure large-scale structures using quasars as direct tracers of dark matter in the redshift range 0.9 〈 z 〈 2.1 and using Ly α forests in quasar spectra at z 〉 2.1. We present several methods to select candidate quasars for DESI, using input photometric imaging in three optical bands ( g , r , z ) from the DESI Legacy Imaging Surveys and two infrared bands (W1, W2) from the Wide-field Infrared Survey Explorer. These methods were extensively tested during the Survey Validation of DESI. In this paper, we report on the results obtained with the different methods and present the selection we optimized for the DESI main survey. The final quasar target selection is based on a random forest algorithm and selects quasars in the magnitude range of 16.5 〈 r 〈 23. Visual selection of ultra-deep observations indicates that the main selection consists of 71% quasars, 16% galaxies, 6% stars, and 7% inconclusive spectra. Using the spectra based on this selection, we build an automated quasar catalog that achieves a fraction of true QSOs higher than 99% for a nominal effective exposure time of ∼1000 s. With a 310 deg −2 target density, the main selection allows DESI to select more than 200 deg −2 quasars (including 60 deg −2 quasars with z 〉 2.1), exceeding the project requirements by 20%. The redshift distribution of the selected quasars is in excellent agreement with quasar luminosity function predictions.
    Type of Medium: Online Resource
    ISSN: 0004-637X , 1538-4357
    URL: Article
    DOI: 10.3847/1538-4357/acb3c2
    RVK:
    UA 1000
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2023
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 1473835-1
    SSG: 16,12
    Location Call Number Limitation Availability
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    Online Resource
  • 2
    Online Resource
    Online Resource
    The Robotic Multiobject Focal Plane System of the Dark Energy Spectroscopic Instrument (DESI)
    American Astronomical Society ; 2023
    In:  The Astronomical Journal Vol. 165, No. 1 ( 2023-01-01), p. 9-
    Details
    In: The Astronomical Journal, American Astronomical Society, Vol. 165, No. 1 ( 2023-01-01), p. 9-
    Abstract: 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.
    Type of Medium: Online Resource
    ISSN: 0004-6256 , 1538-3881
    URL: Article
    DOI: 10.3847/1538-3881/ac9ab1
    RVK:
    US 1090
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2023
    detail.hit.zdb_id: 2207625-6
    detail.hit.zdb_id: 2003104-X
    SSG: 16,12
    Location Call Number Limitation Availability
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    Online Resource
  • 3
    Online Resource
    Online Resource
    The Target-selection Pipeline for the Dark Energy Spectroscopic Instrument
    American Astronomical Society ; 2023
    In:  The Astronomical Journal Vol. 165, No. 2 ( 2023-02-01), p. 50-
    Details
    In: The Astronomical Journal, American Astronomical Society, Vol. 165, No. 2 ( 2023-02-01), p. 50-
    Abstract: In 2021 May, the Dark Energy Spectroscopic Instrument (DESI) began a 5 yr survey of approximately 50 million total extragalactic and Galactic targets. The primary DESI dark-time targets are emission line galaxies, luminous red galaxies, and quasars. In bright time, DESI will focus on two surveys known as the Bright Galaxy Survey and the Milky Way Survey. DESI also observes a selection of “secondary” targets for bespoke science goals. This paper gives an overview of the publicly available pipeline ( desitarget ) used to process targets for DESI observations. Highlights include details of the different DESI survey targeting phases, the targeting ID ( TARGETID ) used to define unique targets, the bitmasks used to indicate a particular type of target, the data model and structure of DESI targeting files, and examples of how to access and use the desitarget code base. This paper will also describe “supporting” DESI target classes, such as standard stars, sky locations, and random catalogs that mimic the angular selection function of DESI targets. The DESI target-selection pipeline is complex and sizable; this paper attempts to summarize the most salient information required to understand and work with DESI targeting data.
    Type of Medium: Online Resource
    ISSN: 0004-6256 , 1538-3881
    URL: Article
    DOI: 10.3847/1538-3881/aca5f9
    RVK:
    US 1090
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2023
    detail.hit.zdb_id: 2207625-6
    detail.hit.zdb_id: 2003104-X
    SSG: 16,12
    Location Call Number Limitation Availability
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    Online Resource
  • 4
    Online Resource
    Online Resource
    The DESI Bright Galaxy Survey: Final Target Selection, Design, and Validation
    American Astronomical Society ; 2023
    In:  The Astronomical Journal Vol. 165, No. 6 ( 2023-06-01), p. 253-
    Details
    In: The Astronomical Journal, American Astronomical Society, Vol. 165, No. 6 ( 2023-06-01), p. 253-
    Abstract: Over the next 5 yr, the Dark Energy Spectroscopic Instrument (DESI) will use 10 spectrographs with 5000 fibers on the 4 m Mayall Telescope at Kitt Peak National Observatory to conduct the first Stage IV dark energy galaxy survey. At z 〈 0.6, the DESI Bright Galaxy Survey (BGS) will produce the most detailed map of the universe during the dark-energy-dominated epoch with redshifts of 〉 10 million galaxies spanning 14,000 deg 2 . In this work, we present and validate the final BGS target selection and survey design. From the Legacy Surveys, BGS will target an r 〈 19.5 mag limited sample (BGS Bright), a fainter 19.5 〈 r 〈 20.175 color-selected sample (BGS Faint), and a smaller low- z quasar sample. BGS will observe these targets using exposure times scaled to achieve homogeneous completeness and cover the footprint three times. We use observations from the Survey Validation programs conducted prior to the main survey along with simulations to show that BGS can complete its strategy and make optimal use of “bright” time. BGS targets have stellar contamination 〈 1%, and their densities do not depend strongly on imaging properties. BGS Bright will achieve 〉 80% fiber assignment efficiency. Finally, BGS Bright and BGS Faint will achieve 〉 95% redshift success over any observing condition. BGS meets the requirements for an extensive range of scientific applications. BGS will yield the most precise baryon acoustic oscillation and redshift-space distortion measurements at z 〈 0.4. It presents opportunities for new methods that require highly complete and dense samples (e.g., N -point statistics, multitracers). BGS further provides a powerful tool to study galaxy populations and the relations between galaxies and dark matter.
    Type of Medium: Online Resource
    ISSN: 0004-6256 , 1538-3881
    URL: Article
    DOI: 10.3847/1538-3881/accff8
    RVK:
    US 1090
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2023
    detail.hit.zdb_id: 2207625-6
    detail.hit.zdb_id: 2003104-X
    SSG: 16,12
    Location Call Number Limitation Availability
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    Online Resource
  • 5
    Online Resource
    Online Resource
    Overview of the DESI Milky Way Survey
    American Astronomical Society ; 2023
    In:  The Astrophysical Journal Vol. 947, No. 1 ( 2023-04-01), p. 37-
    Details
    In: The Astrophysical Journal, American Astronomical Society, Vol. 947, No. 1 ( 2023-04-01), p. 37-
    Abstract: We describe the Milky Way Survey (MWS) that will be undertaken with the Dark Energy Spectroscopic Instrument (DESI) on the Mayall 4 m telescope at the Kitt Peak National Observatory. Over the next 5 yr DESI MWS will observe approximately seven million stars at Galactic latitudes ∣ b ∣ 〉 20°, with an inclusive target selection scheme focused on the thick disk and stellar halo. MWS will also include several high-completeness samples of rare stellar types, including white dwarfs, low-mass stars within 100 pc of the Sun, and horizontal branch stars. We summarize the potential of DESI to advance understanding of the Galactic structure and stellar evolution. We introduce the final definitions of the main MWS target classes and estimate the number of stars in each class that will be observed. We describe our pipelines for deriving radial velocities, atmospheric parameters, and chemical abundances. We use ≃500,000 spectra of unique stellar targets from the DESI Survey Validation program (SV) to demonstrate that our pipelines can measure radial velocities to ≃1 km s −1 and [Fe/H] accurate to ≃0.2 dex for typical stars in our main sample. We find the stellar parameter distributions from ≈100 deg 2 of SV observations with ≳90% completeness on our main sample are in good agreement with expectations from mock catalogs and previous surveys.
    Type of Medium: Online Resource
    ISSN: 0004-637X , 1538-4357
    URL: Article
    DOI: 10.3847/1538-4357/acb3c0
    RVK:
    UA 1000
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2023
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 1473835-1
    SSG: 16,12
    Location Call Number Limitation Availability
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    Online Resource
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