Sloan Digital Sky Survey
Alternative names | SDSS |
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Coordinates | 32°46′50″N 105°49′14″W / 32.7805°N 105.82058°W |
Website | www |
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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.
A consortium of the University of Washington and Princeton University was established to conduct a redshift survey. The Astrophysical Research Consortium (ARC) was established in 1984[1] with the additional participation of New Mexico State University and Washington State University to manage activities at Apache Point. In 1991, the Sloan Foundation granted the ARC funding for survey efforts and the construction of equipment to carry out the work.[2]
Background
At the time of its design, the SDSS was a pioneering combination of novel instrumentation as well as data reduction and storage techniques that drove major advances in astronomical observations, discoveries, and theory.
The SDSS project was centered around two instruments and data processing pipelines that were groundbreaking for the scale at which they were implemented:
- A multi-filter/multi-array scanning CCD camera to take an imaging survey of the sky at high efficiency, followed by
- A multi-object/multi-fiber spectrograph that could take spectra in bulk (several hundred objects at a time) of targets identified from the survey
A major new challenge was how to deal with the exceptional data volume generated by the telescope and instruments. At the time, hundreds of gigabytes of raw data per night was unprecedented, and a collaborating team as complex as the original hardware and engineering team was needed to design a software and storage system for processing the data. From each imaging run, object catalogs, reduced images, and associated files were produced in a highly automated pipeline, yielding the largest astronomical object catalogs (billions of objects) available in digital queryable form at the time. For each spectral run, thousands of two-dimensional spectral images had to be processed to automatically extract calibrated spectra (flux versus wavelength).
In the approximate decade it took to achieve these goals, SDSS contributed to notable advances in massive database storage and accessing technology, such as SQL, and was one of the first major astronomical projects to make data available in this form. The model of giving the scientific community and public broad and internet-accessible access to the survey data products was also relatively new at the time.
The collaboration model around the project was also complex but successful, given the large numbers of institutions and individuals needed to bring expertise to the system. Universities and foundations were participants along with the managing partner ARC. Other participants included
Operation
Data collection began in 2000;[3] the final imaging data release (DR9) covers over 35% of the sky, with photometric observations of around nearly 1 billion objects, while the survey continues to acquire spectra, having so far taken spectra of over 4 million objects. The main galaxy sample has a median redshift of z = 0.1; there are redshifts for luminous red galaxies as far as z = 0.7, and for quasars as far as z = 5; and the imaging survey has been involved in the detection of quasars beyond a redshift z = 6.
Data release 8 (DR8), released in January 2011,
In July 2020, after a 20-year-long survey, astrophysicists of the Sloan Digital Sky Survey published the largest, most detailed 3D map of the universe so far, filled a gap of 11 billion years in its expansion history, and provided data which supports the theory of a flat geometry of the universe and confirms that different regions seem to be expanding at different speeds.[8][9]
Observations
SDSS uses a dedicated 2.5 m wide-angle optical telescope; from 1998 to 2009 it observed in both imaging and spectroscopic modes. The imaging camera was retired in late 2009, since then the telescope has observed entirely in spectroscopic mode.
Images were taken using a photometric system of five filters (named u, g, r, i and z). These images are processed to produce lists of objects observed and various parameters, such as whether they seem pointlike or extended (as a galaxy might) and how the brightness on the CCDs relates to various kinds of astronomical magnitude.
For imaging observations, the SDSS telescope used the
The telescope's imaging camera is made up of 30 CCD chips, each with a resolution of 2048 × 2048
u | g | r | i | z | |
---|---|---|---|---|---|
Mean wavelength (nm) | 355.1 | 468.6 | 616.5 | 748.1 | 893.1 |
Magnitude limit | 22.0 | 22.2 | 22.2 | 21.3 | 20.5 |
Note: colors are only approximate and based on wavelength to sRGB representation.[13]
Using these photometric data, stars, galaxies, and quasars are also selected for
Every night the telescope produces about 200 GB of data.
Phases
SDSS-I: 2000–2005
During its first phase of operations, 2000–2005, the SDSS imaged more than 8,000 square degrees of the sky in five optical bandpasses, and it obtained spectra of galaxies and quasars selected from 5,700 square degrees of that imaging. It also obtained repeated imaging (roughly 30 scans) of a 300 square-degree stripe in the southern Galactic cap.
SDSS-II: 2005–2008
In 2005 the survey entered a new phase, the SDSS-II, by extending the observations to explore the structure and stellar makeup of the Milky Way, the SEGUE and the Sloan Supernova Survey, which watches after supernova Ia events to measure the distances to far objects.
Sloan Legacy Survey
The Sloan Legacy Survey covers over 7,500 square degrees of the Northern Galactic Cap with data from nearly 2 million objects and spectra from over 800,000 galaxies and 100,000 quasars. The information on the position and distance of the objects has allowed the large-scale structure of the Universe, with its voids and filaments, to be investigated for the first time. Almost all of these data were obtained in SDSS-I, but a small part of the footprint was finished in SDSS-II.[16]
Sloan Extension for Galactic Understanding and Exploration (SEGUE)
The Sloan Extension for Galactic Understanding and Exploration obtained spectra of 240,000 stars (with a typical radial velocity of 10 km/s) to create a detailed three-dimensional map of the Milky Way.[17] SEGUE data provide evidence for the age, composition and phase space distribution of stars within the various Galactic components, providing crucial clues for understanding the structure, formation and evolution of our galaxy.
The stellar spectra, imaging data, and derived parameter catalogs for this survey are publicly available as part of SDSS Data Release 7 (DR7).[18]
Sloan Supernova Survey
The SDSS Supernova Survey, which ran from 2005 to 2008, performed repeat imaging of one stripe of sky 2.5° wide centered on the celestial equator, going from 20 hours
SDSS III: 2008–2014
This section needs to be updated. The reason given is: the text has been changed to past-tense, but no new information has been added since the survey was completed.(January 2020) |
In mid-2008, SDSS-III was started. It comprised four separate surveys:[22]
APO Galactic Evolution Experiment (APOGEE)
The APO Galactic Evolution Experiment (APOGEE) used high-resolution, high signal-to-noise infrared spectroscopy to penetrate the dust that obscures the inner Galaxy.[23] APOGEE surveyed 100,000 red giant stars across the full range of the galactic bulge, bar, disk, and halo. It increased the number of stars observed at high spectroscopic resolution (R ≈ 20,000 at λ ≈ 1.6 μm) and high signal-to-noise ratio (100∶1) by more than a factor of 100.[24] The high-resolution spectra revealed the abundances of about 15 elements, giving information on the composition of the gas clouds the red giants formed from. APOGEE planned to collect data from 2011 to 2014, with the first data released as part of SDSS DR10 in late 2013.[25]
Baryon Oscillation Spectroscopic Survey (BOSS)
The SDSS-III's Baryon Oscillation Spectroscopic Survey (BOSS) was designed to measure the expansion rate of the Universe.[26] It mapped the spatial distribution of luminous red galaxies (LRGs) and quasars to determine their spatial distribution and detect the characteristic scale imprinted by baryon acoustic oscillations in the early universe. Sound waves that propagate in the early universe, like spreading ripples in a pond, imprint a characteristic scale on the positions of galaxies relative to each other. It was announced that BOSS had measured the scale of the universe to an accuracy of one percent, and was completed in Spring 2014.[27]
Multi-object APO Radial Velocity Exoplanet Large-area Survey (MARVELS)
The Multi-object APO Radial Velocity Exoplanet Large-area Survey (MARVELS) monitored the radial velocities of 11,000 bright stars, with the precision and cadence needed to detect gas giant planets that have orbital periods ranging from several hours to two years. This ground-based Doppler survey [28] used the SDSS telescope and new multi-object Doppler instruments to monitor radial velocities.[28]
The main goal of the project was to generate a large-scale, statistically well-defined sample of
The collected data was used as a statistical sample for the theoretical comparison and discovery of rare systems.[30] The project started in the fall of 2008, and continued until spring 2014.[28][31]
SEGUE-2
The original Sloan Extension for Galactic Understanding and Exploration (SEGUE-1) obtained spectra of nearly 240,000 stars of a range of spectral types. Building on this success, SEGUE-2 spectroscopically observed around 120,000 stars, focusing on the in situ stellar halo of the Milky Way, from distances of 10 to 60 kpc. SEGUE-2 doubled the sample size of
Combining SEGUE-1 and 2 revealed the complex kinematic and chemical substructure of the galactic halo and disks, providing essential clues to the assembly and enrichment history of the galaxy. In particular, the outer halo was expected to be dominated by late-time accretion events. SEGUE data can help constrain existing models for the formation of the stellar halo and inform the next generation of high-resolution simulations of galaxy formation. In addition, SEGUE-1 and SEGUE-2 may help uncover rare, chemically primitive stars that are fossils of the earliest generations of cosmic star formation.
SDSS IV: 2014–2020
The latest generation of the SDSS (SDSS-IV, 2014–2020) is extending precision cosmological measurements to a critical early phase of cosmic history (eBOSS), expanding its infrared spectroscopic survey of the Galaxy in the northern and southern hemispheres (APOGEE-2), and for the first time using the Sloan spectrographs to make spatially resolved maps of individual galaxies (MaNGA).[34]
APO Galactic Evolution Experiment (APOGEE-2)
A stellar survey of the Milky Way, with two major components: a northern survey using the bright time at APO, and a southern survey using the 2.5 m Du Pont Telescope at Las Campanas.
Extended Baryon Oscillation Spectroscopic Survey (eBOSS)
A cosmological survey of quasars and galaxies, also encompassing subprograms to survey variable objects (TDSS) and X-ray sources (SPIDERS).
Mapping Nearby Galaxies at APO (MaNGA)
MaNGA (Mapping Nearby Galaxies at Apache Point Observatory), explored the detailed internal structure of nearly 10,000 nearby galaxies from 2014 to the spring of 2020. Earlier SDSS surveys only allowed spectra to be observed from the center of galaxies. By using two-dimensional arrays of optical fibers bundled together into a hexagonal shape, MaNGA was able to use spatially resolved spectroscopy to construct maps of the areas within galaxies, allowing deeper analysis of their structure, such as radial velocities and star formation regions.[35][36]
SDSS-V: 2020–current
Apache Point Observatory in New Mexico began to gather data for SDSS-V in October 2020. Apache Point is scheduled to be converted by mid-2021 from plug plates (aluminum plates with manually-placed holes for starlight to shine through) to small automated robot arms, with Las Campanas Observatory in Chile following later in the year. The Milky Way Mapper survey will target the spectra of six million stars. The Black Hole Mapper survey will target galaxies to indirectly analyze their supermassive black holes. The Local Volume Mapper will target nearby galaxies to analyze their clouds of interstellar gas.[37][38]
Data access
The survey makes the data releases available over the Internet. The SkyServer provides a range of interfaces to an underlying Microsoft SQL Server. Both spectra and images are available in this way, and interfaces are made very easy to use so that, for example, a full-color image of any region of the sky covered by an SDSS data release can be obtained just by providing the coordinates. The data are available for non-commercial use only, without written permission. The SkyServer also provides a range of tutorials aimed at everyone from schoolchildren up to professional astronomers. The tenth major data release, DR10, released in July 2013,[7] provides images, imaging catalogs, spectra, and redshifts via a variety of search interfaces.
The raw data (from before being processed into databases of objects) are also available through another Internet server and first experienced as a 'fly-through' via the
The data is also available on
There is also the ever-growing list of data for the Stripe 82 region of the SDSS.
Following Technical Fellow Jim Gray's contribution on behalf of Microsoft Research with the SkyServer project, Microsoft's WorldWide Telescope makes use of SDSS and other data sources.[40]
MilkyWay@home also used SDSS's data to create a highly accurate three-dimensional model of the Milky Way galaxy.
Results
Along with publications describing the survey itself, SDSS data have been used in publications over a huge range of astronomical topics. The SDSS website has a full list of these publications covering distant quasars at the limits of the observable universe,[41] the distribution of galaxies, the properties of stars in our galaxy and also subjects such as dark matter and dark energy in the universe.
Maps
Based on the release of Data Release 9 a new 3D map of massive galaxies and distant black holes was published on August 8, 2012.[42]
See also
- Alex Szalay
- Alfred P. Sloan Foundation
- Apache Point Observatory
- Dark Energy Spectroscopic Instrument
- Galaxy color-magnitude diagram
- Galaxy Zoo
- James E. Gunn
- Sloan Great Wall
References
- ^ Peterson, Jim. "A Brief History of the Astrophysical Research Consortium (ARC) and the Apache Point Observatory (APO)" (PDF). Astrophysical Research Consortium.
- ISBN 978-0-521-89994-9.
- doi:10.1086/500975.
- ^ "SDSS Data Release 8". sdss3.org. Retrieved 2011-01-10.
- ^ "SDSS Data Release 9". sdss3.org. Retrieved 2012-07-31.
- ^ "New 3D Map of Massive Galaxies and Black Holes Offers Clues to Dark Matter, Dark Energy" (Press release). New York University. 8 August 2012.
- ^ a b "SDSS Data Release 10". sdss3.org. Retrieved 2013-08-04.
- ^ "Largest-ever 3D map of the universe released by scientists". Sky News. Retrieved 18 August 2020.
- ^ "No need to Mind the Gap: Astrophysicists fill in 11 billion years of our universe's expansion history". SDSS. Retrieved 18 August 2020.
- ^ David Rabinowitz (2005). "Drift Scanning (Time-Delay Integration)" (PDF). Archived from the original (PDF) on 2007-11-29. Retrieved 2006-12-27.
{{cite journal}}
: Cite journal requires|journal=
(help) - ^ "Key Components of the Survey Telescope". SDSS. 2006-08-29. Archived from the original on 2007-01-07. Retrieved 2006-12-27.
- ^ "SDSS Data Release 7 Summary". SDSS. 2011-03-17.
- ^ "Light wavelength to RGB Converter". www.johndcook.com. Retrieved 2023-07-28.
- S2CID 119434705. Retrieved 3 December 2012.
- ^ "Quasars Acting as Gravitational Lenses". ESA/Hubble Picture of the Week. Retrieved 19 March 2012.
- ^ "About the SDSS Legacy Survey".
- ^ "Sloan Extension for Galactic Understanding and Exploration". segue.uchicago.edu. Archived from the original on 2008-02-19. Retrieved 2008-02-27.
- S2CID 39279981.
- S2CID 53135988.
- S2CID 10089918.
- S2CID 118342974.
- ^ "SDSS-III: Four Surveys Executed Simultaneously - SDSS-III".
- ^ "Sdss-III". Sdss3.org. Retrieved 2011-08-14.
- ^ "SDSS-III: Massive Spectroscopic Surveys of the Distant Universe, the Milky Way Galaxy, and Extra-Solar Planetary Systems" (PDF). Jan 2008. pp. 29–40.
- S2CID 7356513.
- ^ "BOSS: Dark Energy and the Geometry of Space". SDSS III. Retrieved 26 September 2011.
- ^ "BOSS: Dark Energy and the Geometry of Space - SDSS-III". Archived from the original on 2011-01-14.
- ^ a b c d "Sdss-III". Sdss3.org. Retrieved 2011-08-14.
- ^ Publicado por Fran Sevilla. "Carnival of Space #192: Exoplanet discovery and characterization". Vega 0.0. Archived from the original on 2011-04-23. Retrieved 2011-08-14.
- ^ "The Multi-Object APO Radial-Velocity Exoplanet Large-area Survey (MARVELS)". aspbooks.org. Retrieved 2011-08-14.
- ^ Matt Rings (2011-01-23). "Collaboration results in largest-ever image of the night-time sky". Gizmag.com. Retrieved 2011-08-14.
- ^ "Sdss-III". Sdss3.org. Retrieved 2011-08-14.
- ^ "Monster in the deep". www.spacetelescope.org. Retrieved 30 April 2018.
- ^ "Sloan Digital Sky Surveys | SDSS".
- ^ a b "MaNGA | SDSS". www.sdss.org. Retrieved 2017-04-18.
- S2CID 53707289.
- .
- S2CID 230583048.
- ^ "Google Earth KML: SDSS layer". Archived from the original on 2008-03-17. Retrieved 2008-03-24.
- ^ "When did Microsoft first starting looking at the sky?". worldwidetelescope.org. Archived from the original on 2008-03-02. Retrieved 2008-03-24.
- ^ "SDSS Scientific and Technical Publications". sdss.org. Archived from the original on 2008-02-17. Retrieved 2008-02-27.
- ^ "SDSS Science Results" (Press release). sdss3.org. Retrieved 2012-08-08.
Further reading
- Ann K. Finkbeiner. A Grand and Bold Thing: An Extraordinary New Map of the Universe Ushering In A New Era of Discovery (2010), a journalistic history of the project
External links
- NASA Astronomy Picture of the Day: The Sloan Great Wall: Largest Known Structure? (7 November 2007)
- NASA Astronomy Picture of the Day: A Flight Through The Universe (13 August 2012)