Dark Energy Survey
Alternative names | DES |
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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 Víctor 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[update] the DES collaboration has published results from the first three years of the survey.[7]
DECam
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 173 K (−148 °F; −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 0.00013 pascals (1.3×10−9 atm) 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 spanning 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
The scientific
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]
Other surveys using DECam
After completion of the Dark Energy Survey, the Dark Energy Camera was used for other sky surveys:
- Dark Energy Camera Legacy Survey (DECaLS) covers the sky below 32°Declination, not including the Milky Way. This survey covers over 9000 square degrees.[16][17]
- The DESI Legacy Imaging Survey (Legacy Surveys), as of data release 10, includes DECaLS, BASS and MzLS. It also incorporating additional DECam data, which means that it covers almost the entire extragalactic southern sky, including parts of the Magellanic Clouds. The purpose of the Legacy Surveys is to find targets for the Dark Energy Spectroscopic Instrument.[17][18]
- Dark Energy Camera Plane Survey (DECaPS), covers the Milky Way in the southern sky.[19]
Observing
Each year from August through February, observers will stay in dormitories on the mountain. During a weeklong period of work, observers sleep during the day and use the telescope and camera at night. There will be some DES members working at the telescope console to monitor operations while others are monitoring camera operations and data process.
For the wide-area footprint observations, DES takes roughly every two minutes for each new image: The exposures are typically 90 seconds long, with another 30 seconds for readout of the camera data and slewing to point the telescope at its next target. Despite the restrictions on each exposure, the team also need to consider different sky conditions for the observations, such as moonlight and cloud cover.
In order to get better images, DES team use a
Results
Cosmology
Dark Energy Group published several papers presenting their results for
For the first-year data collected by DES, Dark Energy Survey Group showed the Cosmological Constraints results from Galaxy Clustering and Weak Lensing results and cosmic shear measurement. With Galaxy Clustering and Weak Lensing results, and for
For the third-year data collected by DES, they updated the Cosmological Constraints to for the ΛCDM model with the new cosmic shear measurements.[25] From third-year data of Galaxy Clustering and Weak Lensing results, DES updated the Cosmological Constraints to and in ΛCDM at 68% confidence limits, , and in ωCDM at 68% confidence limits.[26] Similarly, the DES team published their third-year observations for photometric data set for cosmology comprising nearly 5000 deg2 of grizY imaging in the south Galactic cap, including nearly 390 million objects, with depth reaching S/N ~ 10 for extended objects up to ~ 23.0, and top-of-the-atmosphere photometric uniformity < 3mmag.[27]
Weak lensing
Weak lensing was measured statistically by measuring the shear-shear
Another big part of weak lensing result is to calibrate the redshift of the source galaxies. In December 2020 and June 2021, DES team published two papers showing their results about using weak lensing to calibrate the redshift of the source galaxies in order to mapping the matter density field with gravitational lensing.[38][39]
Gravitational waves
After LIGO detected the first gravitational wave signal from GW170817,[40] DES made follow-up observations of GW170817 using DECam. With DECam independent discovery of the optical source, DES team establish its association with GW170817 by showing that none of the 1500 other sources found within the event localization region could plausibly be associated with the event. DES team monitored the source for over two weeks and provide the light curve data as a machine-readable file. From the observation data set, DES concluded that the optical counterpart they have identified near NGC 4993 is associated with GW170817. This discovery ushers in the era of multi-messenger astronomy with gravitational waves and demonstrates the power of DECam to identify the optical counterparts of gravitational-wave sources.[41]
Dwarf galaxies
In March 2015, two teams released their discoveries of several new potential dwarf galaxy candidates found in Year 1 DES data.[42] In August 2015, the Dark Energy Survey team announced the discovery of eight additional candidates in Year 2 DES data.[43] Later on, Dark Energy Survey team found more dwarf galaxies. With more Dwarf Galaxy results, the team was able to take a deep look about more properties of the detected Dwarf Galaxy such as the chemical abundance,[44] the structure of stellar population,[45] and Stellar Kinematics and Metallicities.[46] In Feb 2019, the team also discovered a sixth star cluster in the Fornax Dwarf Spheroidal Galaxy[47] and a tidally Disrupted Ultra-Faint Dwarf Galaxy.[48]
Baryon acoustic oscillations
The signature of baryon acoustic oscillations (BAO) can be observed in the distribution of tracers of the matter density field and used to measure the expansion history of the Universe. BAO can also be measured using purely photometric data, though at less significance.[49] DES team observation samples consists of 7 million galaxies distributed over a footprint of 4100 deg2 with 0.6 < zphoto < 1.1 and a typical redshift uncertainty of 0.03(1+z).[50] From their statistics, they combine the likelihoods derived from angular correlations and spherical harmonics to constrain the ratio of comoving angular diameter distance at the effective redshift of our sample to the sound horizon scale at the drag epoch.[51]
Type Ia supernova observations
In May 2019, Dark Energy Survey team published their first cosmology results using
Minor planets
Several
List of DES discovered minor planets Numbered MP
designationDiscovery
dateMP list link Ref (451657) 2012 WD3619 November 2012 list [58] (471954) 2013 RM988 September 2013 list [59] (472262) 2014 QN44118 August 2014 list [60] (483002) 2014 QS44119 August 2014 list [61] (491767) 2012 VU11315 November 2012 list [62] (491768) 2012 VV11315 November 2012 list [63] (495189) 2012 VR11328 September 2012 list [64] (495190) 2012 VS11312 November 2012 list [65] (495297) 2013 TJ15913 October 2013 list [66] Discoveries are credited either to
"DECam" or "Dark Energy Survey".
The MPC has assigned the
Gallery
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Dark Energy Survey deep field image[68]
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The large spiral galaxy in the center of this image is roughly 385 million light-years from Earth.
-
The three large objects in this image captured by the Dark Energy Camera are galaxies in the nearby Fornax cluster, roughly 65 million light-years from Earth.
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Dark Energy Survey - galaxy NGC 1398
See also
References
- ^ "Home". The Dark Energy Survey.
- ^ DES Collaboration Page, DES Collaborators.
- ^ DES-Brazil Archived 2014-10-22 at the Wayback Machine, DES-Brazil Consortium.
- ^ "The Dark Energy Survey Collaboration". www.darkenergysurvey.org. Retrieved 2015-11-21.
- ^ The Project - The Dark Energy Survey Collaboration, The DES Project Site.
- ^ a b c Dark Energy Camera (DECam) Archived 2019-05-23 at the Wayback Machine, Cerro Tololo Inter-American Observatory.
- ^ "DES Year 3 Cosmology Results: Papers". The Dark Energy Survey. Retrieved 3 August 2021.
- ^ "A Sky Full of Galaxies". NOIRLab. Retrieved 12 March 2021.
- ^ 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.
- ^ "Camera | SDSS".
- S2CID 121613505– via www.spiedigitallibrary.org.
- ^ a b "NOAO: A Survey Machine and a Data Trove – Dark Energy Survey's Rich Legacy | CTIO". www.ctio.noao.edu. Archived from the original on 22 September 2021. Retrieved 3 August 2021.
- ^ Dark Energy Survey Collaboration. "Description of the Dark Energy Survey for Astronomers" (PDF). The Dark Energy Survey. Retrieved 1 March 2015.
- ^ "Dark energy camera snaps first images ahead of survey". BBC. 2012-09-18.
- ^ "The Dark Energy Survey begins". Fermilab. 2013-09-03.
- ^ Survey, Legacy (2012-11-08). "The Dark Energy Camera Legacy Survey (DECaLS)". Legacy Survey. Retrieved 2023-12-31.
- ^ ISSN 0004-6256.
- ^ Survey, Legacy (2023-09-28). "Data Release Description". Legacy Survey. Retrieved 2023-12-31.
- ISSN 0067-0049.
- ^ "Observations". The Dark Energy Survey. Survey and operations.
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- ^ ISSN 0035-8711.
- ^ S2CID 235242965.
- ^ "The Dark Energy Survey Science Program" (PDF). Archived from the original (PDF) on 2011-07-20. Retrieved 2010-12-02.
- ^ "Mapping the cosmos: Dark Energy Survey creates detailed guide to spotting dark matter". 13 April 2015.
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- ^ "Scientists find rare dwarf satellite galaxy candidates in Dark Energy Survey data". 10 March 2015.
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- ^ "JPL Small-Body Database Browser". ssd.jpl.nasa.gov. 2 451657.
- ^ Chamberlin, Alan. "JPL Small-Body Database Browser". ssd.jpl.nasa.gov. 2 471954.
- ^ "JPL Small-Body Database Browser". ssd.jpl.nasa.gov. 2 472262.
- ^ "JPL Small-Body Database Browser". ssd.jpl.nasa.gov. 2 483002.
- ^ "JPL Small-Body Database Browser". ssd.jpl.nasa.gov. 2 491767.
- ^ "JPL Small-Body Database Browser". ssd.jpl.nasa.gov. 2 491768.
- ^ "JPL Small-Body Database Browser". ssd.jpl.nasa.gov. 2 495189.
- ^ "JPL Small-Body Database Browser". ssd.jpl.nasa.gov. 2 495190.
- ^ "JPL Small-Body Database Browser". ssd.jpl.nasa.gov. 2 495297.
- ^ "Minor Planet Discoverers (by number)". Minor Planet Center. 15 November 2016. Retrieved 27 January 2017.
- ^ "Dark Energy Survey Releases Most Precise Look at the Universe's Evolution". NOIRLab Press Release. Retrieved 17 June 2021.
External links
- Dark Energy Survey website
- Dark Energy Survey Science Program (PDF)
- Dark Energy Survey Data Management
- Dark Energy Camera (DECam) Archived 2017-10-18 at the Wayback Machine
- Biron, Lauren (4 October 2022). "15 spectacular photos from the Dark Energy Camera". symmetry magazine.