Dark Energy Survey

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The Dark Energy Survey
Dark Energy Survey logo.jpg
Dark Energy Survey logo
Alternative namesDES
Survey typeastronomical survey Edit this on Wikidata
Targetdark energy Edit this on Wikidata
ObservationsCerro Tololo Inter-American Observatory Edit this on Wikidata
Websitewww.darkenergysurvey.org
Commons page Related media on Wikimedia Commons
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The Dark Energy Survey (DES) is an astronomical survey designed to constrain the properties of dark energy. It uses images taken in the near-ultraviolet, visible, and near-infrared to measure the expansion of the Universe using Type Ia supernovae, baryon acoustic oscillations, the number of galaxy clusters, and weak gravitational lensing.[1] The collaboration is composed of research institutions and universities from the United States,[2] Australia, Brazil,[3] the United Kingdom, Germany, Spain, and Switzerland. The collaboration is divided into several scientific working groups. The director of DES is Josh Frieman.[4]

The DES began by developing and building Dark Energy Camera (DECam), an instrument designed specifically for the survey.[5] This camera has a wide field of view and high sensitivity, particularly in the red part of the visible spectrum and in the near infrared.[6] Observations were performed with DECam mounted on the 4-meter Victor M. Blanco Telescope, located at the Cerro Tololo Inter-American Observatory (CTIO) in Chile.[6] Observing sessions ran from 2013 to 2019; as of 2021 the DES collaboration has published results from the first three years of the survey.[7]

DECam[]

A Sky Full of Galaxies.[8]

DECam, short for the Dark Energy Camera, is a large camera built to replace the previous prime focus camera on the Victor M. Blanco Telescope. The camera consists of three major components: mechanics, optics, and CCDs.

Mechanics[]

The mechanics of the camera consists of a filter changer with an 8-filter capacity and shutter. There is also an optical barrel that supports 5 corrector lenses, the largest of which is 98 cm in diameter. These components are attached to the CCD focal plane which is cooled to −100 °C with liquid nitrogen in order to reduce thermal noise in the CCDs. The focal plane is also kept in an extremely low vacuum of 10−6 Torr to prevent the formation of condensation on the sensors. The entire camera with lenses, filters, and CCDs weighs approximately 4 tons. When mounted at the prime focus it was supported with a hexapod system allowing for real time focal adjustment.[9]

Optics[]

The camera is outfitted with u, g, r, i, z, and Y filters spaccing roughly from 340–1070 nm,[10] similar to those used in the Sloan Digital Sky Survey (SDSS). This allows DES to obtain photometric redshift measurements to z≈1. DECam also contains five lenses acting as corrector optics to extend the telescope's field of view to a diameter of 2.2°, one of the widest fields of view available for ground-based optical and infrared imaging.[6] One significant difference between previous charge-coupled devices (CCD) at the Victor M. Blanco Telescope and DECam is the improved quantum efficiency in the red and near-infrared wavelengths.[11][9]

CCDs[]

Simulated image of the DECam CCD array at focal plane. Each large rectangle is a single CCD. The green rectangle circled in red in the upper left corner shows the size of the iPhone 4 camera CCD at the same scale.

The scientific sensor array on DECam is an array of 62 2048×4096 pixel back-illuminated CCDs totaling 520 megapixels; an additional 12 2048×2048 pixel CCDs (50 Mpx) are used for guiding the telescope, monitoring focus, and alignment. The full DECam focal plane contains 570 megapixels. The CCDs for DECam use high resistivity silicon manufactured by Dalsa and LBNL with 15×15 micron pixels. By comparison, the OmniVision Technologies back-illuminated CCD that was used in the iPhone 4 has a 1.75×1.75 micron pixel with 5 megapixels. The larger pixels allow DECam to collect more light per pixel, improving low light sensitivity which is desirable for an astronomical instrument. DECam's CCDs also have a 250-micron crystal depth; this is significantly larger than most consumer CCDs. The additional crystal depth increases the path length travelled by entering photons. This, in turn, increases the probability of interaction and allows the CCDs to have an increased sensitivity to lower energy photons, extending the wavelength range to 1050 nm. Scientifically this is important because it allows one to look for objects at a higher redshift, increasing statistical power in the studies mentioned above. When placed in the telescope's focal plane each pixel has a width of 0.263″ on the sky, resulting in a total field of view of 3 square degrees.

Survey[]

DES imaged 5,000 square degrees of the southern sky in a footprint that overlaps with the South Pole Telescope and Stripe 82 (in large part avoiding the Milky Way). The survey took 758 observing nights spread over six annual sessions between August and February to complete, covering the survey footprint ten times in five photometric bands (g, r, i, z, and Y).[12] The survey reached a depth of 24th magnitude in the i band over the entire survey area. Longer exposure times and faster observing cadence were made in five smaller patches totaling 30 square degrees to search for supernovae.[13]

First light was achieved on 12 September 2012;[14] after a verification and testing period, scientific survey observations started in August 2013.[15] The last observing session was completed on 9 January 2019.[12]

Results[]

Weak lensing[]

Weak lensing was measured statistically by measuring the shear-shear correlation function, a two-point function, or its Fourier Transform, the shear power spectrum.[16] In April 2015, the Dark Energy Survey released mass maps using cosmic shear measurements of about 2 million galaxies from the science verification data between August 2012 and February 2013.[17]

Dwarf galaxies[]

In March 2015, two teams released their discoveries of several new potential dwarf galaxies candidates found in Year 1 DES data.[18] In August 2015, the Dark Energy Survey team announced the discovery of eight additional candidates in Year 2 DES data.[19]

Minor planets[]

Several minor planets were discovered by DeCam in the course of The Dark Energy Survey, including high-inclination trans-Neptunian objects (TNOs).[20] The MPC has assigned the IAU code W84 for DeCam's observations of small Solar System bodies. As of October 2019, the MPC inconsistently credits the discovery of 9 numbered minor planets, all of them trans-Neptunian objects, to either "DeCam" or "Dark Energy Survey".[21] The list does not contain any unnumbered minor planets potentially discovered by DeCam, as discovery credits are only given upon a body's numbering, which in turn depends on a sufficiently secure orbit determination.

List of discovered minor planets[]

(451657) 2012 WD36 [22] 19 November 2012 list
(471954) 2013 RM98 [23] 8 September 2013 list
(472262) 2014 QN441 [24] 18 August 2014 list
(483002) 2014 QS441 [25] 19 August 2014 list
(491767) 2012 VU113 [26] 15 November 2012 list
(491768) 2012 VV113 [27] 15 November 2012 list
(495189) 2012 VR113 [28] 28 September 2012 list
(495190) 2012 VS113 [29] 12 November 2012 list
(495297) 2013 TJ159 [30] 13 October 2013 list
Discoveries are credited to "DECam" and "Dark Energy Survey", respectively.

Gallery[]

  • Dark Energy Survey deep field image
    [31]
  • The Dark Energy Camera's 1 millionth exposure. At the time of this exposure DECam was making an image of a galaxy cluster.
    [32]

References[]

  1. ^ "Home". The Dark Energy Survey.
  2. ^ DES Collaboration Page, DES Collaborators.
  3. ^ DES-Brazil Archived 2014-10-22 at the Wayback Machine, DES-Brazil Consortium.
  4. ^ "The Dark Energy Survey Collaboration". www.darkenergysurvey.org. Retrieved 2015-11-21.
  5. ^ The Project - The Dark Energy Survey Collaboration, The DES Project Site.
  6. ^ Jump up to: a b c Dark Energy Camera (DECam), Cerro Tololo Inter-American Observatory.
  7. ^ "DES Year 3 Cosmology Results: Papers". The Dark Energy Survey. Retrieved 3 August 2021.
  8. ^ "A Sky Full of Galaxies". https://noirlab.edu/. Retrieved 12 March 2021. External link in |website= (help)
  9. ^ Jump up to: a b DECam Presentation Archived 2011-09-27 at the Wayback Machine, Pdf Presentation about the specific details about how a CCD device works and about the specific properties of the DECam, made by a Fermilab specialist.
  10. ^ "Camera | SDSS".
  11. ^ Flaugher, Brenna L.; et al. (September 24, 2012). "Status of the Dark Energy Survey Camera (DECam) project". International Society for Optics and Photonics. p. 844611. doi:10.1117/12.926216 – via www.spiedigitallibrary.org.
  12. ^ Jump up to: a b "NOAO: A Survey Machine and a Data Trove – Dark Energy Survey's Rich Legacy | CTIO". www.ctio.noao.edu. Retrieved 3 August 2021.
  13. ^ Dark Energy Survey Collaboration. "Description of the Dark Energy Survey for Astronomers" (PDF). The Dark Energy Survey. Retrieved 1 March 2015.
  14. ^ "Dark energy camera snaps first images ahead of survey". BBC. 2012-09-18.
  15. ^ "The Dark Energy Survey begins". Fermilab. 2013-09-03.
  16. ^ "The Dark Energy Survey Science Program" (PDF). Archived from the original (PDF) on 2011-07-20. Retrieved 2010-12-02.
  17. ^ "Mapping the cosmos: Dark Energy Survey creates detailed guide to spotting dark matter".
  18. ^ "Scientists find rare dwarf satellite galaxy candidates in Dark Energy Survey data".
  19. ^ "Eight Ultra-faint Galaxy Candidates Discovered in Year Two of the Dark Energy Survey". The Astrophysical Journal. 813 (2): 109. November 4, 2015. arXiv:1508.03622. doi:10.1088/0004-637X/813/2/109 – via arXiv.org.
  20. ^ DES Collaboration (2018). "DISCOVERY AND DYNAMICAL ANALYSIS OF AN EXTREME TRANS-NEPTUNIAN OBJECT WITH A HIGH ORBITAL INCLINATION". The Astronomical Journal. 156 (2): 81. arXiv:1805.05355. doi:10.3847/1538-3881/aad042. S2CID 55163842.
  21. ^ "Minor Planet Discoverers (by number)". Minor Planet Center. 15 November 2016. Retrieved 27 January 2017.
  22. ^ "JPL Small-Body Database Browser". ssd.jpl.nasa.gov.
  23. ^ Chamberlin, Alan. "JPL Small-Body Database Browser". ssd.jpl.nasa.gov.
  24. ^ "JPL Small-Body Database Browser". ssd.jpl.nasa.gov.
  25. ^ "JPL Small-Body Database Browser". ssd.jpl.nasa.gov.
  26. ^ "JPL Small-Body Database Browser". ssd.jpl.nasa.gov.
  27. ^ "JPL Small-Body Database Browser". ssd.jpl.nasa.gov.
  28. ^ "JPL Small-Body Database Browser". ssd.jpl.nasa.gov.
  29. ^ "JPL Small-Body Database Browser". ssd.jpl.nasa.gov.
  30. ^ "JPL Small-Body Database Browser". ssd.jpl.nasa.gov.
  31. ^ "Dark Energy Survey Releases Most Precise Look at the Universe's Evolution". NOIRLab Press Release. Retrieved 17 June 2021.
  32. ^ "DECam Takes Millionth Exposure". NOIRLab Press Release. Retrieved 17 June 2021.

External links[]

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