The Sloan Digital Sky Survey Jon Loveday University of Sussex

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The Sloan Digital Sky SurveyJon
LovedayUniversity of Sussex

• http//www.sdss.org

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Brief Autobiography

• 1985-1989 University of Cambridge (PhD
  supervised by George Efstathiou)
• 1989-1992 Mt Stromlo Observatory
• 1992-1996 Fermilab
• 1996-2000 University of Chicago
• 2000-present University of Sussex

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Outline

• SDSS overview
• Survey status
• Illustrative science results
• Asteroids
• Dwarf Stars
• Supernovae
• Milky Way dwarf satellites
• Galaxy formation and evolution
• Cosmological constraints
• Beyond SDSS

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Survey Goal A Roadmap of the Sky

• Image 1/4 of the sky in five colours ugriz
• Measure 50 million galaxy images to r22
• Obtain spectra for 1 million galaxies and
  100,000 quasars

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Science Goals

• May be summarized by the following two STFC key
  science questions
• What is the universe made of and how does it
  evolve?
• How do galaxies, stars and planets form and
  evolve?

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SDSS1 Collaboration

• University of Chicago
• Fermilab
• Institute for Advanced Study
• Japan Participation Group
• Johns Hopkins University
• Los Alamos National Lab

• Max Planck Institutes for Astronomy and
  Astrophysics
• New Mexico State University
• University of Pittsburgh
• Princeton University
• US Naval Observatory
• University of Washington

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Fermilab, April 2001
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Survey SiteApache Point Observatory, New Mexico
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2.5m Telescope

• Modified Ritchey-Chretien design with 3 degree
  field of view.
• Alt-azimuth mount. Roll-off enclosure.
• Independently mounted wind and light baffles.

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Imaging and Spectroscopy

• Imaging
• near-simultaneous imaging in five passbands
  (ugriz) to r22 via drift scanning
• Uses best observing conditions (no cloud or moon,
  seeing lt 1.5 arcsec)
• Spectroscopy
• 640 fibre multiplex system
• Targets based on imaging data
• Uses poorer observing conditions

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SDSS Filters
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Imaging Camera
6 x 5 x 2048 x 2048 0.4 pixels 120 Mpix
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Drift-Scan Observing

• Effective exposure time 55 s
• Two interlacing strips make up a 2.5 deg wide
  stripe

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Survey Area
Survey Area
SGP
NGP
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Spectrographs

• 2 Dual-beam spectrographs (red blue cameras)
• 320 fibres per spectrograph, hand plugged
• Wavelength range 3900-9100 Å
• Resolution ?/d? 2000
• Total throughput 20 in blue, 25 in red

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Spectroscopic Samples

• Main galaxy sample
• Flux-limited
• 900,000 galaxies to r 17.77
• Luminous red galaxies (LRGs)
• Approx volume limited to z 0.4
• 100,000 galaxies selected by colour and photo-z
  to r 19.5.
• Quasars - 100,000 selected by colour/radio
• Stars Serendipity

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Software

• Imaging pipelines reduce imaging data, apply
  photometric and astrometric calibration
• Target Selection automated selection of targets
  for spectroscopy
• Tiling optimal placing of spectroscopic plates
  and allocation of optical fibres
• Spectroscopic pipeline automated redshift
  determination

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Survey Status

• Operations began 2000
• Six public data releases to date
• SDSS2 commenced July 2005
• Legacy survey (complete original goals)
• SEGUE (Galactic structure)
• Supernovae (from repeated imaging of southern
  equatorial stripe)

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Data Release 6

• Published June 2007
• Imaging area 9583 deg2
• Photometry of 287 million unique objects
• Spectra of 1.2 million objects over 6860 deg2
  including
• 790,860 galaxies 103,647 quasars
  287,071 stars

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Legacy Imaging
Legacy Spectroscopy
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Science Results

• A very brief survey of SDSS results from our own
  solar system, via stars and galaxies, to
  cosmology
• As of 17 August 2007, 2160 scientific papers on
  the Astrophysics Data System have SDSS or
  Sloan Digital Sky Survey in the title

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Asteroids

• SDSS is great at detecting moving objects
• Asteroids on similar orbits have similar colours
• Suggests common origin of asteroid families

Ivezic et al 2002
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Discovery of M, L and T dwarfs

• Cool stars drop out of bluer filters

Near-IR spectrum of a methane dwarf (Hawley et
al. 2002)
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Pre-CV Binary Stars

• Hundreds of white dwarf - red dwarf pairs found
  by their unusual colours and spectra
• Precursors to cataclysmic variables (CVs) and
  supernovae
• Clues to evolution of binary systems

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SDSS Supernova Survey

• 322 confirmed type Ia SNe in redshift range 0.1
  lt z lt 0.3 from 2005 2006 seasons
• Test for evolution in SN luminosities no
  correlations of SN luminosity with galaxy
  properties found
• Probes epoch of dark energy domination

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Milky Way Dwarf Satellites

• Dwarf galaxies contain at most only a few million
  stars (cf 1011 stars in the Milky Way)
• Predicted to form in great abundance in
  hierarchical galaxy formation as expected in cold
  dark matter models
• Prior to 2005, Milky Way had only 12 known dwarf
  satellites, far fewer than predicted
• Deep, multi-colour imaging has enabled SDSS to
  find 8 new MW dwarfs since 2005

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Leo T Dwarf Galaxy

• D 1.4 million light years
• L 50,000 L?
• May be a free-floating Local Group dwarf,
  rather than a satellite of the Milky Way
• One of a large population of very faint Local
  Group dwarfs?

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Galaxy Properties - I Luminosity Function

• Number density of galaxies as function of
  intrinsic luminosity or absolute magnitude
• Successful models of galaxy formation must
  successfully predict this
• Surveys are biased against low surface-brightness
  and dwarf galaxies - must correct for this

Blanton et al 2005
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II Bimodality and Correlations
bright Luminosity faint compact Shape diffuse b
right Surface brightness faint red Colour blue
Blanton et al 2005
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III Low luminosity galaxies
Blanton et al 2005
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Galaxy Clustering

• Measurements of galaxy clustering help to
  constrain
• Cosmological models ?0, ?,
• Models of galaxy formation
• Two point correlation function ?(r) excess
  probability (above random) of finding two
  galaxies at separation r dP 1
  ?(r12)dV1dV2
• Fourier transform of power spectrum P(k)

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Colour dependence
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Luminosity dependence
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Relative Galaxy Clustering

• Red, early type (elliptical) galaxies are
  clustered more strongly, and more tightly, than
  blue, late type (spiral) galaxies
• Luminous galaxies are more strongly clustered
  than less luminous galaxies, but with an
  apparently scale-independent bias to r 10 Mpc
  scales
• Nature versus nuture how does a galaxys
  environment determine its properties?

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High Redshift Quasars
Fan et al. 2001, AJ, 122, 2833
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z 6.4 Quasar
Gunn-PetersonTrough
Fan et al 2003
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Large-Scale Structure
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Concordance Cosmology

• All current observations are consistent with a
  Universe dominated by dark energy

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Cmbgg OmOl
CMB

LSS
WMAP only SDSS
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Baryon acoustic peak

• Before recombination photons and electrons were
  tightly coupled ? attractive force of gravity
  opposed by photon pressure ? sound waves
• Preferred scale of 100 h-1Mpc frozen in at
  recombination (z 1000)
• Gives rise to 1 degree preferred scale in
  cosmic microwave background anisotropy, detected
  by COBE and WMAP

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0.12 ?mh2 0.13
0.14 Fixed ?bh2 0.024, n 0.98 No baryons
Eisenstein et al 2005
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What does it mean?

• We have detected the sound wave in the Universe
  at two very different epochs (400,000 yrs after
  Big Bang and present-day)
• This is important because our theory of
  gravitational structure formation predicts that
  such features should have been preserved
• Better yet, the sound wave is an object of fixed
  size, a standard ruler
• By measuring its angular size at different
  redshifts, we can determine the geometry of the
  Universe

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Looking back in time in the Universe
Looking back in time in the Universe
CMB
SDSS GALAXIES
FLAT GEOMETRY
FLAT GEOMETRY
CREDIT WMAP SDSS websites
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Looking back in time in the Universe
Looking back in time in the Universe
CMB
SDSS GALAXIES
FLAT GEOMETRY
OPEN GEOMETRY
CREDIT WMAP SDSS websites
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Looking back in time in the Universe
Looking back in time in the Universe
CMB
SDSS GALAXIES
FLAT GEOMETRY
CLOSED GEOMETRY
CREDIT WMAP SDSS websites
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UNIVERSE IS FLAT TO 1 PRECISION
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Lessons Learned from SDSS

• SDSS was first really large (100 scientists)
  ground-based astronomy project good
  communication (meetings, web pages) is vital
• Dont underestimate software requirements!
• Well calibrated, multi-colour imaging data
  perhaps even more important than 1 million
  redshifts
• Expect the unexpected! Dont design a survey
  around too narrow goals

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Beyond SDSS I Large imaging surveys

• UKIDSS (2005-2012) VISTA (2008-) (near-IR)
• Dark Energy Survey (DES) 500 Mpixel camera on
  CTIO 4m (2008-2013)
• Pan-STARRS 4x1.8m telescopes each with a
  Giga-pixel camera with 3? field of view (2007-)
• Large Synoptic Survey Telescope (LSST) 8.4m
  telescope with 10? field of view (proposed)
• Both Pan-STARRS and LSST will observe all
  available sky every few nights

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Beyond SDSS II Large spectroscopic surveys

• Baryon Oscillation Spectroscopic Survey (BOSS
  2009-2014)
• Use upgraded SDSS spectrograph to measure
  redshifts of 1.5 million luminous red galaxies
  (LRGs) to z 0.7
• Wide Field Multi-Object Spectrograph (WFMOS)
• 4500 fibres in 1.5? field of view on Gemini or
  Subaru telescope first light in 2012
• SDSS at z 1
• Key science goal of both projects will be to
  constrain evolution of dark energy

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Square Kilometre Array (SKA)

• Aperture synthesis telescope with 1 square km
  collecting area
• Whole sky redshift survey to z 3 from HI 21cm
  line
• One billion HI redshifts to z 1.5 in 1 year of
  operation (starting 2020)

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http//www.sdss.org