ORCID Profile
0000-0003-1887-1018
Current Organisations
University of California, Berkeley
,
E O Lawrence Berkeley National Laboratory
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Publisher: American Physical Society (APS)
Date: 09-04-2004
Publisher: American Astronomical Society
Date: 07-12-2022
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 in idual 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.
Publisher: American Astronomical Society
Date: 03-03-2023
Abstract: We describe the spectroscopic data processing pipeline of the Dark Energy Spectroscopic Instrument (DESI), which is conducting a redshift survey of about 40 million galaxies and quasars using a purpose-built instrument on the 4 m Mayall Telescope at Kitt Peak National Observatory. The main goal of DESI is to measure with unprecedented precision the expansion history of the universe with the baryon acoustic oscillation technique and the growth rate of structure with redshift space distortions. Ten spectrographs with three cameras each disperse the light from 5000 fibers onto 30 CCDs, covering the near-UV to near-infrared (3600–9800 Å) with a spectral resolution ranging from 2000 to 5000. The DESI data pipeline generates wavelength- and flux-calibrated spectra of all the targets, along with spectroscopic classifications and redshift measurements. Fully processed data from each night are typically available to the DESI collaboration the following morning. We give details about the pipeline’s algorithms, and provide performance results on the stability of the optics, the quality of the sky background subtraction, and the precision and accuracy of the instrumental calibration. This pipeline has been used to process the DESI Survey Validation data set, and has exceeded the project’s requirements for redshift performance, with high efficiency and a purity greater than 99% for all target classes.
Publisher: American Physical Society (APS)
Date: 25-11-2003
Publisher: American Physical Society (APS)
Date: 1988
Publisher: American Physical Society (APS)
Date: 06-1988
Publisher: SPIE
Date: 09-07-2018
DOI: 10.1117/12.2312140
Publisher: American Physical Society (APS)
Date: 26-09-2003
Publisher: American Physical Society (APS)
Date: 18-02-2004
Publisher: American Physical Society (APS)
Date: 18-03-2004
Publisher: American Physical Society (APS)
Date: 14-02-2002
Publisher: American Physical Society (APS)
Date: 13-02-2002
Publisher: American Physical Society (APS)
Date: 19-09-2003
Publisher: American Physical Society (APS)
Date: 15-04-2002
Publisher: American Astronomical Society
Date: 02-2023
Abstract: We present Dark Energy Spectroscopic Instrument (DESI) observations of the inner halo of M31, which reveal the kinematics of a recent merger—a galactic immigration event—in exquisite detail. Of the 11,416 sources studied in 3.75 hr of on-sky exposure time, 7438 are M31 sources with well-measured radial velocities. The observations reveal intricate coherent kinematic structure in the positions and velocities of in idual stars: streams, wedges, and chevrons. While hints of coherent structures have been previously detected in M31, this is the first time they have been seen with such detail and clarity in a galaxy beyond the Milky Way. We find clear kinematic evidence for shell structures in the Giant Stellar Stream, the Northeast Shelf, and Western Shelf regions. The kinematics are remarkably similar to the predictions of dynamical models constructed to explain the spatial morphology of the inner halo. The results are consistent with the interpretation that much of the substructure in the inner halo of M31 is produced by a single galactic immigration event 1–2 Gyr ago. Significant numbers of metal-rich stars ([Fe/H] − 0.5) are present in all of the detected substructures, suggesting that the immigrating galaxy had an extended star formation history. We also investigate the ability of the shells and Giant Stellar Stream to constrain the gravitational potential of M31, and estimate the mass within a projected radius of 125 kpc to be log 10 M NFW ( 125 kpc ) / M ⊙ = 11.80 − 0.10 + 0.12 . The results herald a new era in our ability to study stars on a galactic scale and the immigration histories of galaxies.
Publisher: American Physical Society (APS)
Date: 13-11-2003
Publisher: American Physical Society (APS)
Date: 05-04-2004
Publisher: American Physical Society (APS)
Date: 05-03-1990
Publisher: American Astronomical Society
Date: 10-2020
Abstract: The DESI survey will measure large-scale structure using quasars as direct tracers of dark matter in the redshift range 0.9 z 2.1 and using quasar Ly α forests at z 2.1. We present two methods to select candidate quasars for DESI based on imaging in three optical ( g , r , z ) and two infrared ( W 1, W 2) bands. The first method uses traditional color cuts and the second utilizes a machine-learning algorithm.
Publisher: American Astronomical Society
Date: 02-2023
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.
Publisher: American Astronomical Society
Date: 04-2023
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 s les 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 s le. We find the stellar parameter distributions from ≈100 deg 2 of SV observations with ≳90% completeness on our main s le are in good agreement with expectations from mock catalogs and previous surveys.
Publisher: American Astronomical Society
Date: 11-04-2019
Publisher: American Physical Society (APS)
Date: 06-05-2003
Publisher: American Physical Society (APS)
Date: 31-03-2004
Publisher: American Physical Society (APS)
Date: 29-06-2004
Publisher: American Physical Society (APS)
Date: 08-05-2003
Publisher: American Physical Society (APS)
Date: 06-05-2004
Publisher: American Physical Society (APS)
Date: 23-04-2004
Publisher: American Physical Society (APS)
Date: 10-03-2004
Publisher: American Physical Society (APS)
Date: 02-04-2004
Publisher: American Physical Society (APS)
Date: 25-02-1991
Publisher: Elsevier BV
Date: 04-1990
Publisher: Springer Science and Business Media LLC
Date: 09-1989
DOI: 10.1007/BF01506527
Publisher: American Astronomical Society
Date: 2023
Abstract: The Dark Energy Spectroscopic Instrument (DESI) Survey has obtained a set of spectroscopic measurements of galaxies to validate the final survey design and target selections. To assist in these tasks, we visually inspect DESI spectra of approximately 2500 bright galaxies, 3500 luminous red galaxies (LRGs), and 10,000 emission-line galaxies (ELGs) to obtain robust redshift identifications. We then utilize the visually inspected redshift information to characterize the performance of the DESI operation. Based on the visual inspection (VI) catalogs, our results show that the final survey design yields s les of bright galaxies, LRGs, and ELGs with purity greater than 99%. Moreover, we demonstrate that the precision of the redshift measurements is approximately 10 km s −1 for bright galaxies and ELGs and approximately 40 km s −1 for LRGs. The average redshift accuracy is within 10 km s −1 for the three types of galaxies. The VI process also helps improve the quality of the DESI data by identifying spurious spectral features introduced by the pipeline. Finally, we show ex les of unexpected real astronomical objects, such as Ly α emitters and strong lensing candidates, identified by VI. These results demonstrate the importance and utility of visually inspecting data from incoming and upcoming surveys, especially during their early operation phases.
Publisher: American Physical Society (APS)
Date: 03-1990
Publisher: American Physical Society (APS)
Date: 17-06-2003
Publisher: American Physical Society (APS)
Date: 09-11-2004
Publisher: Elsevier BV
Date: 10-1989
Publisher: American Physical Society (APS)
Date: 20-05-2002
Publisher: American Physical Society (APS)
Date: 20-05-2002
Publisher: American Physical Society (APS)
Date: 15-08-2002
Publisher: American Physical Society (APS)
Date: 07-01-2002
Publisher: American Physical Society (APS)
Date: 26-02-2004
Publisher: American Physical Society (APS)
Date: 27-02-2003
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 08-1990
DOI: 10.1109/23.55862
Publisher: American Physical Society (APS)
Date: 29-01-2004
Publisher: American Physical Society (APS)
Date: 30-01-2004
Publisher: American Physical Society (APS)
Date: 03-06-2002
Publisher: SPIE
Date: 06-07-2018
DOI: 10.1117/12.2313063
Publisher: American Physical Society (APS)
Date: 23-10-2003
Publisher: American Physical Society (APS)
Date: 11-12-2003
Publisher: Springer Science and Business Media LLC
Date: 11-2014
Publisher: Elsevier BV
Date: 09-1989
Publisher: American Physical Society (APS)
Date: 20-05-2002
Publisher: American Physical Society (APS)
Date: 13-06-2002
Publisher: IOP Publishing
Date: 10-2023
Publisher: American Physical Society (APS)
Date: 26-02-0001
Publisher: American Astronomical Society
Date: 22-02-2023
Abstract: A key component of the Dark Energy Spectroscopic Instrument (DESI) survey validation (SV) is a detailed visual inspection (VI) of the optical spectroscopic data to quantify key survey metrics. In this paper we present results from VI of the quasar survey using deep coadded SV spectra. We show that the majority (≈70%) of the main-survey targets are spectroscopically confirmed as quasars, with ≈16% galaxies, ≈6% stars, and ≈8% low-quality spectra lacking reliable features. A nonnegligible fraction of the quasars are misidentified by the standard spectroscopic pipeline, but we show that the majority can be recovered using post-pipeline “afterburner” quasar-identification approaches. We combine these “afterburners” with our standard pipeline to create a modified pipeline to increase the overall quasar yield. At the depth of the main DESI survey, both pipelines achieve a good-redshift purity (reliable redshifts measured within 3000 km s −1 ) of ≈99% however, the modified pipeline recovers ≈94% of the visually inspected quasars, as compared to ≈86% from the standard pipeline. We demonstrate that both pipelines achieve a median redshift precision and accuracy of ≈100 km s −1 and ≈70 km s −1 , respectively. We constructed composite spectra to investigate why some quasars are missed by the standard pipeline and find that they are more host-galaxy dominated (i.e., distant analogs of “Seyfert galaxies”) and/or more dust reddened than the standard-pipeline quasars. We also show ex le spectra to demonstrate the overall ersity of the DESI quasar s le and provide strong-lensing candidates where two targets contribute to a single spectrum.
Publisher: American Physical Society (APS)
Date: 25-02-2004
Publisher: American Astronomical Society
Date: 26-05-2023
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 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 s le (BGS Bright), a fainter 19.5 r 20.175 color-selected s le (BGS Faint), and a smaller low- z quasar s le. 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 %, and their densities do not depend strongly on imaging properties. BGS Bright will achieve % fiber assignment efficiency. Finally, BGS Bright and BGS Faint will achieve % 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 s les (e.g., N -point statistics, multitracers). BGS further provides a powerful tool to study galaxy populations and the relations between galaxies and dark matter.
Location: United States of America
Location: United States of America
No related grants have been discovered for Michael Levi.