Dark Energy Spectroscopic Instrument

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Dark Energy Spectroscopic Instrument
DESI crossfade 4 (sunset-Workup-04-CC).tiff
DESI installed on the Nicholas U. Mayall 4-meter Telescope at Kitt Peak National Observatory
Alternative namesDESI OOjs UI icon edit-ltr-progressive.svg
Part of Kitt Peak National Observatory
Nicholas U. Mayall Telescope   OOjs UI icon edit-ltr-progressive.svg
Location(s) Kitt Peak, Arizona
Coordinates 31°57′51″N111°36′00″W / 31.96406°N 111.6°W / 31.96406; -111.6 OOjs UI icon edit-ltr-progressive.svg
Organization Lawrence Berkeley National Laboratory   OOjs UI icon edit-ltr-progressive.svg
Altitude2,100 m (6,900 ft) OOjs UI icon edit-ltr-progressive.svg
Wavelength 360 nm (830 THz)–980 nm (310 THz)
Built2015– (2015–) OOjs UI icon edit-ltr-progressive.svg
First light 2019  OOjs UI icon edit-ltr-progressive.svg
Telescope style scientific instrument
spectrometer   OOjs UI icon edit-ltr-progressive.svg
Website desi.lbl.gov OOjs UI icon edit-ltr-progressive.svg
Usa edcp relief location map.png
Red pog.svg
Location of Dark Energy Spectroscopic Instrument
  Commons-logo.svg Related media on Commons

The Dark Energy Spectroscopic Instrument (DESI) is a scientific research instrument for conducting spectrographic astronomical surveys of distant galaxies. Its main components are a focal plane containing 5,000 fiber-positioning robots, and a bank of spectrographs which are fed by the fibers. The instrument enables an experiment to probe the expansion history of the universe and the mysterious physics of dark energy. [1] [2] The main DESI survey started in May 2021. DESI sits at an elevation of 6,880 feet (2,100 m), where it has been retrofitted onto the Mayall Telescope on top of Kitt Peak in the Sonoran Desert, which is located 55 miles (89 km) from Tucson, Arizona, US.

Contents

The instrument is operated by the Lawrence Berkeley National Laboratory under funding from the US Department of Energy's Office of Science. Construction of the instrument was principally funded by the US Department of Energy's Office of Science, and by other numerous sources including the US National Science Foundation, the UK Science and Technology Facilities Council, France's Alternative Energies and Atomic Energy Commission, Mexico's National Council of Science and Technology, Spain's Ministry of Science and Innovation, by the Gordon and Betty Moore Foundation, by the Heising-Simons Foundation, and by collaborating institutions worldwide. [3] [4]

Science goals

An artistic celebration of the Dark Energy Spectroscopic Instrument (DESI) year-one data, showing a slice of the larger 3D map that DESI is constructing during its five-year survey. Artistic Composition of DESI Year-One Data Slice Above the Nicholas U Mayall 4-meter Telescope (noirlab2408a).jpg
An artistic celebration of the Dark Energy Spectroscopic Instrument (DESI) year-one data, showing a slice of the larger 3D map that DESI is constructing during its five-year survey.

The expansion history and large-scale structure of the universe is a key prediction of cosmological models, and DESI observations will permit scientists to probe diverse aspects of cosmology, from dark energy to alternatives to General Relativity to neutrino masses to the early universe. The data from DESI will be used to create three-dimensional maps of the distribution of matter covering an unprecedented volume of the universe with unparalleled detail. This will provide insight into the nature of dark energy and establish whether cosmic acceleration is due to a cosmic-scale modification of General Relativity. DESI will be transformative in the understanding of dark energy and the expansion rate of the universe at early times, one of the greatest mysteries in the understanding of the physical laws.

DESI will measure the expansion history of the universe using the baryon acoustic oscillations (BAO) imprinted in the clustering of galaxies, quasars, and the intergalactic medium. [5] The BAO technique is a robust way to extract cosmological distance information from the clustering of matter and galaxies. It relies only on very large-scale structure and it does so in a manner that enables scientists to separate the acoustic peak of the BAO signature from uncertainties in most systematic errors in the data. BAO was identified in the 2006 Dark Energy Task Force report as one of the key methods for studying dark energy. [6] In May 2014, the High-Energy Physics Advisory Panel, a federal advisory committee, commissioned by the US Department of Energy (DOE) and the National Science Foundation (NSF) endorsed DESI. [7]

3D map of the universe

Comparison of the Sloan survey at left consisting of around 4 million galaxies and quasars taken from 2000 to 2020 and the DESI survey at right consisting of around 7.5 million during its 7 first months starting in 2021 and expected to be completed by 2026 with 35 million. Sloan2020vsDESI2022.jpg
Comparison of the Sloan survey at left consisting of around 4 million galaxies and quasars taken from 2000 to 2020 and the DESI survey at right consisting of around 7.5 million during its 7 first months starting in 2021 and expected to be completed by 2026 with 35 million.

The baryon acoustic oscillations method requires a three-dimensional map of distant galaxies and quasars created from the angular and redshift information of a large statistical sample of cosmologically distant objects. By obtaining spectra of distant galaxies it is possible to determine their distance, via the measurement of their spectroscopic redshift, and thus create a 3-D map of the universe. [10] The 3-D map of the large-scale structure of the universe also contains more information about dark energy than just the BAO and is sensitive to the mass of the neutrino and parameters that governed the primordial universe. During its five-year survey, which began on May 15, 2021, the DESI experiment is expected to observe 40 million galaxies and quasars. [11]

Development

The DESI instrument implements a new highly multiplexed optical spectrograph on the Mayall Telescope. [12] The new optical corrector design creates a very large, 8.0 square degree field of view on the sky, which combined with the new focal plane instrumentation weighs approximately 10 tonnes. The focal plane accommodates 5,000 small computer controlled fiber positioners on a 10.4 millimeter pitch. The entire focal plane can be reconfigured for the next exposure in less than two minutes while the telescope slews to the next field. The DESI instrument is capable of taking 5,000 simultaneous spectra over a wavelength range from 360 nm to 980 nm. The DESI project scope included construction, installation, and commissioning of the new wide-field corrector and corrector support structure for the telescope, the focal plane assembly with 5,000 robotic fiber positioners and ten guide/focus/alignment sensors, a 40-meter optical fiber cabling system that brings light from the focal plane to the spectrographs, ten 3-arm spectrographs, an instrument control system, and a data analysis pipeline.

The instrument fabrication was managed by the Lawrence Berkeley National Laboratory and oversees operation of the experiment including a 600-person international scientific collaboration. Cost of construction was $56M from the US Department of Energy's Office of Science plus an additional $19M from other non-federal sources including contributions in-kind. The leadership of DESI currently consists of the director, Dr. Michael E. Levi, collaboration co-spokespersons Prof. Kyle Dawson and Dr. Nathalie Palanque-Delabrouille, project scientists Dr. David J. Schlegel and Dr. Julien Guy, project manager Dr. Patrick Jelinsky, instrument scientists Prof. Klaus Honscheid and Prof. Constance Rockosi. Past collaboration spokespersons have been Prof. Daniel Eisenstein and Prof. Risa Wechsler.

DOE approved CD-0 (Mission Need) on September 18, 2012, approved CD-1 (Alternative Selection and Cost Range) on March 19, 2015, and CD-2 (Performance Baseline) on September 17, 2015. Congressional approval for the start of DESI as a new Major Item of Equipment was provided in the FY15 Energy & Water appropriations legislation. Construction on the new instrument started June 22, 2016 with CD-3 (Start Construction) approval and was largely assembled by 2019 with commissioning finishing in March 21, 2020 in advance of the pandemic and marking the formal end of the project (CD-4). [13] DESI was completed under budget by $1.9M and 17 months ahead of schedule. As a consequence, the project received the DOE Project Management Excellence Award for 2020. [14] After a pause for the pandemic and a transition to remote operations, DESI returned to survey operations in December, 2020 with a final checkout and validation phase prior to starting its planned five-year survey. The five-year survey began on May 14, 2021. [15] DESI was shut down for three months in the summer of 2022 due to the Contreras fire which engulfed Kitt Peak. DESI was undamaged and is acquiring scientific data. [16]

DESI Legacy Imaging Surveys

To provide targets for the DESI survey three telescopes surveyed the northern and part of the southern sky in the g, r and z-band. Those surveys were the Beijing-Arizona Sky Survey (BASS), using the Bok 2.3-m telescope, the Dark Energy Camera Legacy Survey (DECaLS), using the Blanco 4m telescope and the Mayall z-band Legacy Survey (MzLS), using the 4-meter Mayall telescope. The area of the surveys is 14,000 square degrees (about one third of the sky) and avoids the Milky Way. These surveys were combined into the DESI Legacy Imaging Surveys, or Legacy Surveys. [17] [18] Colored images of the survey can be viewed in the Legacy Survey Sky Browser. [19] The legacy survey covers 16,000 square degrees of the night sky containing 1.6 billion objects including galaxies and quasars out to 11 billion years ago.

History

DESI received a go-ahead to start R&D for the project in December 2012 with the assignment of the Lawrence Berkeley National Laboratory as the managing laboratory. Dr. Michael Levi, a senior scientist at the Lawrence Berkeley National Laboratory was appointed by the laboratory to be DESI's project director who served in that role starting in 2012 and throughout construction. Henry Heetderks was project manager from 2013 until 2016, Robert Besuner was project manager from 2016 until 2020. Congressional authorization was provided in 2015, and the US Department of Energy's Office of Science approved the start of physical construction in June 2016. First light of the new corrector system was obtained on the night of April 1, 2019, and first-light of the entire instrument was achieved on the night of October 22, 2019. Commissioning ensued after first light and was completed in March, 2020, then paused during the pandemic in 2020. [20] DESI started its 5-year main scientific survey on May 14, 2021. DESI is currently operating normally after surviving the Contreras fire in 2022. [21]

Data Releases

Example spectrum taken by DESI for the Early Data Release. The image shows the spectrum of the galaxy LEDA 1787534. DESI EDR example galaxy LEDA 1787534.png
Example spectrum taken by DESI for the Early Data Release. The image shows the spectrum of the galaxy LEDA 1787534.

All of the publicly available data including redshift catalogs, added-value catalogs, and documentation, can be accessed through DESI sata portal. Individuals with accounts at the National Energy Research Scientific Computing Center (NERSC) can access the entire public portion of the DESI data. DESI catalogs also exist in a database format. For convenience, a copy of the public databases is also hosted by the NOIRLab Astro Data Lab science platform, and by using the SPectral Analysis and Retrievable Catalog Lab (SPARCL). [22] One easy way to access DESI spectra online is to use the legacy viewer at the DESI Legacy Imaging Surveys. [23] Users have to check the box for DESI spectra and click on an encircled galaxy or star for a link to the DESI Spectral Viewer to show up. [24] The spectrum can be explored in the DESI Spectral Viewer. [25] (Please see External Links under Index| Legacy Surveys)

Early Data Release

On 13 June 2023 the DESI Early Data Release (EDR) was announced. [26] The EDR contains spectra of nearly two million galaxies, quasars and stars. [22] One early result of the EDR was announced in February 2023 and described a mass migration of stars into the Andromeda Galaxy. [27] The EDR also revealed very distant quasars and very metal-poor stars. [22] [28]

Possibly evolving dark energy levels

From the level of detail able to be observed, the largest 3-D map of the universe at this point has been created (2024). [29] From this precise data, DESI Director Michael Levi stated:

We’re also seeing some potentially interesting differences that could indicate that dark energy is evolving over time. Those may or may not go away with more data, so we’re excited to start analyzing our three-year dataset soon. [30]

Related Research Articles

<span class="mw-page-title-main">Kitt Peak National Observatory</span> United States astronomical observatory

The Kitt Peak National Observatory (KPNO) is a United States astronomical observatory located on Kitt Peak of the Quinlan Mountains in the Arizona-Sonoran Desert on the Tohono Oʼodham Nation, 88 kilometers (55 mi) west-southwest of Tucson, Arizona. With more than twenty optical and two radio telescopes, it is one of the largest gatherings of astronomical instruments in the Earth's northern hemisphere.

<span class="mw-page-title-main">Quasar</span> Active galactic nucleus containing a supermassive black hole

A quasar is an extremely luminous active galactic nucleus (AGN). It is sometimes known as a quasi-stellar object, abbreviated QSO. The emission from an AGN is powered by a supermassive black hole with a mass ranging from millions to tens of billions of solar masses, surrounded by a gaseous accretion disc. Gas in the disc falling towards the black hole heats up and releases energy in the form of electromagnetic radiation. The radiant energy of quasars is enormous; the most powerful quasars have luminosities thousands of times greater than that of a galaxy such as the Milky Way. Quasars are usually categorized as a subclass of the more general category of AGN. The redshifts of quasars are of cosmological origin.

<span class="mw-page-title-main">Redshift</span> Change of wavelength in photons during travel

In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation. The opposite change, a decrease in wavelength and increase in frequency and energy, is known as a blueshift, or negative redshift. The terms derive from the colours red and blue which form the extremes of the visible light spectrum. The main causes of electromagnetic redshift in astronomy and cosmology are the relative motions of radiation sources, which give rise to the relativistic Doppler effect, and gravitational potentials, which gravitationally redshift escaping radiation. All sufficiently distant light sources show cosmological redshift corresponding to recession speeds proportional to their distances from Earth, a fact known as Hubble's law that implies the universe is expanding.

<span class="mw-page-title-main">Reionization</span> Process that caused matter to reionize early in the history of the Universe

In the fields of Big Bang theory and cosmology, reionization is the process that caused electrically neutral atoms in the universe to reionize after the lapse of the "dark ages".

<span class="mw-page-title-main">Australian Astronomical Observatory</span> Observatory

The Australian Astronomical Observatory (AAO), formerly the Anglo-Australian Observatory, was an optical and near-infrared astronomy observatory with its headquarters in North Ryde in suburban Sydney, Australia. Originally funded jointly by the United Kingdom and Australian governments, it was managed wholly by Australia's Department of Industry, Innovation, Science, Research and Tertiary Education. The AAO operated the 3.9-metre Anglo-Australian Telescope (AAT) and 1.2-metre UK Schmidt Telescope (UKST) at Siding Spring Observatory, located near the town of Coonabarabran, Australia.

<span class="mw-page-title-main">Sloan Digital Sky Survey</span> Multi-spectral imaging and spectroscopic redshift survey

The Sloan Digital Sky Survey or SDSS is a major multi-spectral imaging and spectroscopic redshift survey using a dedicated 2.5-m wide-angle optical telescope at Apache Point Observatory in New Mexico, United States. The project began in 2000 and was named after the Alfred P. Sloan Foundation, which contributed significant funding.

<span class="mw-page-title-main">Redshift survey</span>

In astronomy, a redshift survey is a survey of a section of the sky to measure the redshift of astronomical objects: usually galaxies, but sometimes other objects such as galaxy clusters or quasars. Using Hubble's law, the redshift can be used to estimate the distance of an object from Earth. By combining redshift with angular position data, a redshift survey maps the 3D distribution of matter within a field of the sky. These observations are used to measure detailed statistical properties of the large-scale structure of the universe. In conjunction with observations of early structure in the cosmic microwave background, these results can place strong constraints on cosmological parameters such as the average matter density and the Hubble constant.

<span class="mw-page-title-main">2dF Galaxy Redshift Survey</span>

In astronomy, the 2dF Galaxy Redshift Survey, 2dF or 2dFGRS is a redshift survey conducted by the Australian Astronomical Observatory (AAO) with the 3.9m Anglo-Australian Telescope between 1997 and 11 April 2002. The data from this survey were made public on 30 June 2003. The survey determined the large-scale structure in two large slices of the Universe to a depth of around 2.5 billion light years. It was the world's largest redshift survey between 1998 and 2003. Matthew Colless, Richard Ellis, Steve Maddox and John Peacock were in charge of the project. Team members Shaun Cole and John Peacock were awarded a share of the 2014 Shaw Prize in astronomy for results from the 2dFGRS.

<span class="mw-page-title-main">Astronomical survey</span> General map or image of a region of the sky with no specific observational target

An astronomical survey is a general map or image of a region of the sky that lacks a specific observational target. Alternatively, an astronomical survey may comprise a set of images, spectra, or other observations of objects that share a common type or feature. Surveys are often restricted to one band of the electromagnetic spectrum due to instrumental limitations, although multiwavelength surveys can be made by using multiple detectors, each sensitive to a different bandwidth.

<span class="mw-page-title-main">Joint Dark Energy Mission</span> Proposed space probe

The Joint Dark Energy Mission (JDEM) was an Einstein probe that planned to focus on investigating dark energy. JDEM was a partnership between NASA and the U.S. Department of Energy (DOE).

<span class="mw-page-title-main">Víctor M. Blanco Telescope</span> Telescope located in Chile

The Víctor M. Blanco Telescope, also known as the Blanco 4m, is a 4-metre aperture telescope located at the Cerro Tololo Inter-American Observatory, Chile on the summit of Mt. Cerro Tololo. Commissioned in 1974 and completed in 1976, the telescope is identical to the Mayall 4m telescope located on Kitt Peak. In 1995 it was dedicated and named in honour of Puerto Rican astronomer Víctor Manuel Blanco. It was the largest optical telescope in the Southern hemisphere from 1976 until 1998, when the first 8-metre telescope of the ESO Very Large Telescope opened.

<span class="mw-page-title-main">Nicholas U. Mayall Telescope</span> Four-meter reflector telescope in Pima County, Arizona

The Nicholas U. Mayall Telescope, also known as the Mayall 4-meter Telescope, is a four-meter reflector telescope located at the Kitt Peak National Observatory in Arizona and named after Nicholas U. Mayall. It saw first light on February 27, 1973, and was the second-largest telescope in the world at that time. Initial observers included David Crawford, Nicholas Mayall, and Arthur Hoag. It was dedicated on June 20, 1973 after Mayall's retirement as director. The mirror has an f/2.7 hyperboloidal shape. It is made from a two-foot thick fused quartz disk that is supported in an advanced-design mirror cell. The prime focus has a field of view six times larger than that of the Hale reflector. It is host to the Dark Energy Spectroscopic Instrument. The identical Víctor M. Blanco Telescope was later built at Cerro Tololo Inter-American Observatory, in Chile.

<span class="mw-page-title-main">6dF Galaxy Survey</span>

The 6dF Galaxy Survey, 6dF or 6dFGS is a redshift survey conducted by the Anglo-Australian Observatory (AAO) with the 1.2m UK Schmidt Telescope between 2001 and 2009. The data from this survey were made public on 31 March, 2009. The survey has mapped the nearby universe over nearly half the sky. Its 136,304 spectra have yielded 110,256 new extragalactic redshifts and a new catalog of 125,071 galaxies. For a subsample of 6dF a peculiar velocity survey is measuring mass distribution and bulk motions of the local Universe. As of July 2009, it is the third largest redshift survey next to the Sloan Digital Sky Survey (SDSS) and the 2dF Galaxy Redshift Survey (2dFGRS).

<i>Euclid</i> (spacecraft) European visible and near-infrared space observatory

Euclid is a wide-angle space telescope with a 600-megapixel camera to record visible light, a near-infrared spectrometer, and photometer, to determine the redshift of detected galaxies. It was developed by the European Space Agency (ESA) and the Euclid Consortium and was launched on 1 July 2023 from Cape Canaveral in Florida.

<span class="mw-page-title-main">Michael Lampton</span> American astronaut (1941–2023)

Michael Logan Lampton was an American astronaut, scientist, and founder of the optical ray tracing company Stellar Software. He was also known for his paper on electroacoustics with Susan M Lea, The theory of maximally flat loudspeaker systems.

<span class="mw-page-title-main">WiggleZ Dark Energy Survey</span> Scientific astronomy survey

The WiggleZ Dark Energy Survey is a large-scale astronomical redshift survey that was carried out on the 3.9 metre Anglo-Australian Telescope (AAT) at the Siding Spring Observatory, New South Wales between August 2006 and January 2011. The name stems from the measurement of baryon acoustic oscillations in the distribution of galaxies.

<span class="mw-page-title-main">SPHEREx</span> NASA near-infrared space observatory

SPHEREx is a future near-infrared space observatory that will perform an all-sky survey to measure the near-infrared spectra of approximately 450 million galaxies. In February 2019, SPHEREx was selected by NASA for its next Medium-Class Explorers mission, beating out two competing mission concepts: Arcus and FINESSE. As of August 2022, SPHEREx is targeted to launch no earlier than April 2025 on a Falcon 9 launch vehicle from Vandenberg Space Force Base. The principal investigator is James Bock at California Institute of Technology (Caltech) in Pasadena, California.

David James Schlegel is a Senior Scientist at the Lawrence Berkeley National Laboratory. He earned his Ph.D. in 1995 from the University of California, Berkeley. His earliest research was with Prof. Marc Davis and Douglas Finkbeiner working on dust maps of the universe. This research resulted in one of the most highly cited articles in astronomy. These maps proved to be essential for removing foregrounds in subsequent imaging or cosmic microwave background surveys.

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