Large Scale Surveys

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Large Scale Surveys

• Moumita Aich
• Astronomy Techniques 1
• IUCAA

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Properties of Surveys

• Type and purpose
• General-use or highly specific? Targeted or
  blind? Imaging or spectroscopic?
• Area and spatial resolution
• All-sky, wide-field, pencil-beam?
• Wavelength and spectral resolution
• Broad-band, narrow-band, spectroscopic?
• Depth and quality
• Faintest detections? Reliability? Precision?
• Analysis, storage and use
• Reductions, data volume, dissemination?

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Moores Law in Surveys
The spectra in redshift surveys increase rapidly
per year, following nearly the Moore's Law.
Large number of spectra requires new methods to
consider the higher-dimensional data sets
objectively and automatically, and to reduce the
error rate, e.g., in classification.
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Survey Design Factors

• A? - product of telescope aperture (A) and area
  on sky (?).
• Important figure-of-merit for imaging surveys
  time taken
• to cover given area to survey depth.
• Efficiency e - relative system throughput.
• telescope, instrument, detector throughputs.
• Multiplex - number of objects that can be
  observe
• simultaneously.
• Important figure-of-merit for spectroscopic
  surveys (in
• combination with field-of-view).
• Overheads - non-survey observing time
• Field acquisition, calibrations, readout, etc.

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Example I

• Imaging survey of sky - what combination of
  telescope
• detector is quickest?
• Telescope/instrument
• AAT/WFI has A15m2, ?0.25deg2, e 0.2
  so speed ? A?e 0.75
• UKST/film has A1.5m2, ?25.0deg2, e 0.02 so
  speed ? A?e 0.75
• In this case decision would be based on other
  components of overall survey speed (overheads,
  telescope availability) or survey goals (spatial
  resolution, precision of photometry).

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Example II

• Redshift survey of sky - what combination of
  telescope detector is quickest?
• Survey speed ? A?e /N where N ? max(1,s?/M) is
  the number of times each field must be observed
  and s is surface density of targets.
• Telescope/instrument
• AAT/2dF - A15m2, ?3deg2, e 0.1, M400 so
• speed ? min(4.5,600/s)
• UKST/6dF - A1.5m2, ?30deg2, e 0.2, M150 so
  speed ? min(9,45/ s)
• Hence the crucial factor here is source density.
• if s gt 10deg-2 then use 2dF if s lt 10deg-2
  then use 6dF

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Types of Surveys and Some Useful Examples

• Imaging surveys (various wavelengths)
• Spectroscopic surveys (redshift etc.)
• Surveys of specific object classes
• General-purpose surveys (sky surveys)
• Single-goal surveys (experiments)

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All-Sky Imaging Surveys

• Radio surveys
• FIRST - Faint Images of the Radio Sky at 21-cm,
  
• northern sky down to 0.75mJy.
• NVSS - NRAO VLA Sky Survey, continuum survey at
• 1.4GHz, northern sky above dgt - 40.
• SUMSS - Sydney University Molonglo Sky Survey,
• 843MHz, matching NVSS but in south.
• HIPASS - HI Parkes All-Sky Survey blind HI
  survey of
• southern sky

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VLA image of the galaxy M87
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IR sky surveys

• Exploring the Hidden Universe - extinction of
  the
• interstellar medium is only 10 of that at
  optical
• wavelengths.
• Detecting Cool Objects - clouds of particles
  around
• stars, nebulae, interstellar molecules, brown
  dwarfs
• and planets.
• Exploring the Early Universe - At large z, all
  of the
• ultraviolet and much of the visible light from
  distant
• sources is shifted into the infrared part of
  the spectrum
• by the time it reaches our telescopes.

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• IR sky surveys
• 2MASS - Two-Micron All-Sky Survey (JHK)
• DENIS - Deep Near-Infrared Survey of the
• Southern Sky (IJK)
• IRAS - Infra-Red Astronomy Satellite
• ISA - Infrared Space Observatory - 2.5 to 240
• microns.
• SIRTF SST - Space Telescope (Space Infrared
• Telescope Facility)

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IRAS Infrared Astronomical Satellite

• Launched on January 25,
• 1983.
• Ten months of operation
• Scanned more than 96
• percent of the sky four
• times
• Four infrared bands
• centered at 12, 25, 60
• and 100 microns
• increasing the number of
• cataloged astronomical
• sources by almost 70.

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• GENERAL - Detected 500,000 infrared sources,
  doubling
• the number of cataloged astronomical sources.
• SOLAR SYSTEM - Comets Asteroids.
• STARS AND STAR FORMATION
• Discovered disk of dust grains around stars
  (Vega).
• Detected several probable protostars embedded
  in clouds
• of gas and dust.
• Found that some Bok globules contain
  protostars.
• Cataloged over 12,000 variable stars
  thousands of hot,
• dense cores within clouds of gas and dust
  which could be
• newly forming stars.

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• Milky Way
• Revealed for the first time the core of our
  galaxy
• Found infrared cirrus (wisps of warm dust) in
  almost
• every direction of space.
• Data from IRAS was used to show that our galaxy
  is a
• barred spiral galaxy - a galaxy which has an
  elongated
• central bar-like bulge from which its spiral
  arms unwind.

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GALAXIES

• Detected 75,000 starburst galaxies - galaxies
  which are extremely bright in the infrared due to
  intense star formation. It was found that many of
  these starburst galaxies have "super winds"
  emerging from their centers due to the large
  number of supernova explosions which occur in
  these galaxies.
• Detected strong infrared emission from
  interacting galaxies
• First identified IRAS F102144724 - extremely
  luminous, z 2.3, a narrow arc morphology,
  highly magnified by a foreground gravitational
  lens. This object may be the best candidate for a
  forming spiral galaxy yet discovered.

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• Optical sky surveys
• UKST Southern Sky Surveys (B and R), esp.
  
• APM and SuperCosmos digitized versions
• DSS - Digitized Sky Survey
• HDF - Hubble Deep Field
• DPOSS - Digitized Palomar Observatory Sky
• Survey
• 2dF Galaxy QSO Redshift Survey
• SDSS - Sloan Digital Sky Survey, ugriz over p
• steradians to r 23 in north r 25 in
  southern
• deep strips.

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The Sloan Digital Sky Survey

• 2000 Major ground
• based survey.
• Multi-filter imaging and
• spectroscopic redshift
• survey.
• 2.5 m wide-angle
• optical telescope at
• Apache Point
• Observatory,
• New Mexico.
• 2006 survey entered
• a new phase, the
• SDSS-II.

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Survey Goals

• Map the universe in 3 dimensions over a large
  volume.
• Make definitive map of local universe
• Image p steradians in five colours ugriz.
• Obtain observations on around 108 objects and
  spectra for 1 million objects.
• Obtain spectra for 1 million galaxies to r 22.
• and 105 quasars.
• Main galaxy sample has a median redshift of 0.1
  Involved in the detection of luminous red
  galaxies as far z 0.4, for quasars as far as z
  gt 6.

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Survey Geometry Northern Survey 6,600 sq.
deg Around North Galactic Cap. Southern Survey
3 slices 7,500 square degrees of the Southern
Galactic Cap with data from nearly 2 million
objects and spectra from over 800,000 galaxies
and 100,000 quasars. Sloan Legacy Survey
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SDSS-II - 2006

• SEGUE - Sloan Extension for Galactic
  Understanding and Exploration, spectra of 240,000
  stars with typical radial velocity of 10 km/s for
  obtaining the structure of the Milky Way and
  investigating the formation of components.
  explore the structure and stellar makeup of the
  Milky Way.
• Sloan Supernova Survey
• End of the year 2007- Searches for Type Ia
  supernovae. Scans a 300 square degree area to
  detect variable objects and supernovae.
• Detected 129 confirmed supernovae Ia events in
  2005, and over 300 total during 2005 and 2006.

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• A High Redshift Detection of the Integrated
  Sachs-
• Wolfe Effect
• Sources of Gravitational Lensing
• Large Scale Structure
• Dark Matter Density Profile
• Luminosity Density of Red Galaxies and Galaxy
• Clustering
• Quasar and Galaxy Catalogue

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UV Surveys

• EUVE - Extreme Ultraviolet Explorer (June 7,
  1992)
• 7 and 76 nm
• All-sky survey in the extreme
• uv band
• Deep survey in the EUV range
• on two separate band passes
• Spectroscopic observations
• of targets found by other
• missions
• Observe EUV sources - hot
• white dwarfs and coronal stars
• Study the composition of the
• ISM using EUV spectroscopy

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GALEX - Galaxy Evolution Explorer, orbiting
ultraviolet space telescope April 2003
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X-ray surveys

• RASS ROSAT- Röntgen Satellite (1990),
  whole-sky map and catalogue of 105 sources in
  0.1-2.4keV band.
• All Sky catalogue
• Detailed morphology of supernova
• remnants and clusters of galaxies.
• Detection of shadowing of diffuse
• X- ray emission by molecular
• clouds.
• Detection of pulsations from
• Geminga.
• Detection of isolated neutron stars.
• Discovery of X-ray emission from
• comets.
• Observation of X-ray emission from
• the collision of Comet Shoemaker-
• Levy with Jupiter.

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XMM-Newton - X-ray Multi-Mirror Mission Newton,
orbiting X-ray observatory, December 10, 1999,
Large Scale Structure Survey
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Gamma Ray Surveys
CGRO - Compton Gamma Ray Observatory, 2nd of
NASA's Great Observatories. 17 tons, (April 5,
1991)
Red glow above the Milky Way plane - interpreted
as a region in which antimatter has interacted
with conventional matter, releasing a huge amount
of energy
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Other Surveys

• Gravitational Lens Surveys
• MACHO - microlensing in LMC,SMC and bulge.
• AGAPE - microlensing in Andromeda
• EROS - microlensing in the LMC
• OGLE - microlensing in LMC, SMC and bulge.
• Galaxy Surveys
• APM Galaxy Survey - 2x106 galaxies with
• BJ lt 20.5 in South Galactic Cap.

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Deep Imaging Surveys
Hubble Deep Fields (NS) - deepest optical images
of the universe (also ISO, Chandra, etc deep
fields) EIS - ESO Imaging Survey, O/IR
multi-colour imaging of 6 3x2 patches ELIAS -
ISO deep imaging of 13 at 7, 15, 90, 175mm
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Cosmological Surveys

• COBE - 1989
• WMAP - 2001
• Planck - 2008

Surveys of Magellanic Clouds

• Magellanic Clouds Photometric Survey
• MCELS - Magellanic Cloud Emission Line Survey
• Radio Surveys of the Magellanic Clouds

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Conclusion

• Spectroscopic surveys are essential for
  understanding galaxy formation.
• They provide a platform for science discovery.
• Surveys like SDSS and before have followed
  Moores Law.
• Now they tend to go deeper for higher-redshifts
  objects.
• Many interesting science have been done using
  spectra, but more challenges will likely call for
  more innovative approaches.

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References

• Sky Surveys Protostars to Protogalaxies -
  ASPCS, Volume - 43

Thank You !