Sloan Digital Sky SurveySloan Digital Sky Survey

Astronomy 007Astronomy 007

13 April 200613 April 2006

Margaret FlynnMargaret Flynn

OverviewOverview

• ““The most ambitious astronomical The most ambitious astronomical survery ever undertaken”survery ever undertaken”

• 2.5m telescope based in New Mexico2.5m telescope based in New Mexico

• Ultimate resultsUltimate results– Digital images of more than 25% of skyDigital images of more than 25% of sky– 3-D map of 1,000,000 galaxies and 3-D map of 1,000,000 galaxies and

quasarsquasars

History of the ProjectHistory of the Project

• Begun in 2000 Begun in 2000

• Named for the Alfred P. Sloan Named for the Alfred P. Sloan Foundation, which funded the surveyFoundation, which funded the survey

• Five data releases (EDR, DR1-4), Five data releases (EDR, DR1-4), each covering more area than the each covering more area than the lastlast

Why Map the Sky?Why Map the Sky?• We must understand our current universe We must understand our current universe

to reconstruct cosmic historyto reconstruct cosmic history

• This is a difficult task because of the This is a difficult task because of the amount of dark matteramount of dark matter

• ““By careful mapping of the positions and By careful mapping of the positions and motions of galaxies” we can find clues motions of galaxies” we can find clues about the amount and nature of dark about the amount and nature of dark mattermatter

• Observing galaxies and quasars at Observing galaxies and quasars at different distances, astronomers can see different distances, astronomers can see how their properties change with time how their properties change with time

How Exactly is the Sky How Exactly is the Sky Surveyed?Surveyed?

• SDDS is a redshift survey SDDS is a redshift survey – RedshiftRedshift distance distance

• Obtains high-resolution photos in five Obtains high-resolution photos in five different colorsdifferent colors– Through filters Through filters u, g, r, i, u, g, r, i, and and zz

About the TelescopeAbout the Telescope• Viewing area ≈ 30 full moonsViewing area ≈ 30 full moons• Consists of 2 reflecting mirrors, 2 Consists of 2 reflecting mirrors, 2

corrective lenses for focuscorrective lenses for focus• Photons hit the detectors, CCDs Photons hit the detectors, CCDs

collect themcollect them• CCDs organized into rows, CCDs organized into rows,

which record object’s which record object’s brightness in different colorbrightness in different color

How the Telescope WorksHow the Telescope Works

• Spectrograph analyses each celestial Spectrograph analyses each celestial objects recordedobjects recorded

• Astronomers drill holes Astronomers drill holes corresponding to positions of bodiescorresponding to positions of bodies

• Holes plugged with fibersHoles plugged with fibers– Capture light from the objectsCapture light from the objects– Record results in CCDsRecord results in CCDs

SpectrographsSpectrographs• Device to produce any spectrumDevice to produce any spectrum

• Turns wavelengths of light light from Turns wavelengths of light light from hundreds of galaxies and quasars hundreds of galaxies and quasars into spectra at the same timeinto spectra at the same time– Produces this spectrum through a Produces this spectrum through a

“grism”“grism”– Diffraction grating Diffraction grating

plus prism plus prism

The ObservatoryThe Observatory

• Apache Point Observatory in Apache Point Observatory in Sunspot, NMSunspot, NM

• Houses the telescope, support Houses the telescope, support facilities, dormitoriesfacilities, dormitories

• Altitude is conducive to astronomyAltitude is conducive to astronomy– Little water vaporLittle water vapor– Few contaminantsFew contaminants

After the Images are After the Images are Recorded…Recorded…

• Astronomers process the data to Astronomers process the data to extract information about the extract information about the properties of celestial bodiesproperties of celestial bodies

• Compared to the Yellow PagesCompared to the Yellow Pages

• Importance of processing quicklyImportance of processing quickly

• ““Pipeline”—digital images Pipeline”—digital images star star positionspositions

Some Results Thus Far… Some Results Thus Far…

• Shows us how redshift can Shows us how redshift can

affect the way we see galaxies affect the way we see galaxies

Sloan Digital Sky SurveySloan Digital Sky Survey

The Early Data Release or EDR was released in June 2001 covering 462 square degrees and 53,000 spectra. Data Release 1 or DR1 was released in April 2003 covering 2,099 square degrees and 186,000 spectra. Data Release 2 or DR2 was released in March 2004 covering 3,324 square degrees and 367,000 spectra. Data Release 3 or DR3 was released September 27, 2004, and covers 4,188 square degrees and 528,640 spectra. [1] Date Release 4 or DR4 was released in June 2005 covering 6, 670 square degrees and nearly 850,000 spectra

Images Recorded by SDDSImages Recorded by SDDS

Galaxy NGC3077 in Ursa Major

The Coma cluster of galaxies

A region of the constellation Cygnus

Whirlpool pair of galaxies referred to as M51

Works CitedWorks Cited

• ““Sloan Digital Sky Survey.” 29 March Sloan Digital Sky Survey.” 29 March 2006. Accessed April 11, 20062006. Accessed April 11, 2006

<http://www.sdss.org/sdss.html>.<http://www.sdss.org/sdss.html>.Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia.

Sloan Digital Sky SurveySloan Digital Sky Survey. 5 April . 5 April 2006. Accessed 11 April 20062006. Accessed 11 April 2006<http://en.wikipedia.org/wiki/<http://en.wikipedia.org/wiki/Sloan_Digital_Sky_Survey>.Sloan_Digital_Sky_Survey>.