The 6dF Galaxy Survey

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The 6dF Galaxy Survey
Lesa Moore Macquarie University ASNSW 18th
November 2005
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Outline

• Survey
• Instrumentation
• Spectra
• Redshifts
• Data
• Science
• Movies

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6dF Galaxy Survey

• UK Schmidt Telescope obtaining
• redshifts (z) of 150,000 galaxies
• peculiar velocities (v) of 15,000 galaxies
• Telescope has Six-Degree Field of view
• Redshifts yield 3-D map of universe
• 7 million programme, gt20 scientists worldwide
• 75 of observing time on UKST is dedicated to the
  survey
• Observations from May 2001 to June 2005

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Scope of the Survey

• Full southern hemisphere coverage
• except for zone of avoidance
• (i.e. the Milky Way)
• Objects out to redshift of z 0.1
• Approximate recession velocity 30,000 km/s
• Approximate distance 430 Mpc (1.4 billion ly)
• Looking at the local universe

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Target and Observed Fields

• Plots courtesy Heath Jones (April 2005)
  1360 fields

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Advantages

• Selection in the NIR (2MASS) minimizes extinction
  effects of extinction - galaxies can be selected
  over bgt10.

• NIR luminosity is very closely correlated with
  total stellar mass, and so yields the stellar
  mass function.
• The 6dFGS has 8x the sky coverage of the 2dFGRS
• and twice the coverage of SDSS.
• Images courtesy Heath Jones

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Survey Instrumentation

• UK Schmidt Telescope, Siding Spring
• 6-degree field of view
• Previously used for full hemispheric photographic
  surveys
• 6dfGS is first spectroscopic survey of whole
  southern sky

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The UK Schmidt Telescope

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Specially designed 6dF field plates

• Field plates hold optical fibres with magnetic
  buttons
• 150 fibre buttons, 130 galaxies per field
• Some fibres used for sky subtraction
• Robotic r-theta fibre positioner (1 hour)

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Configure

• Allocation of fibres to
• targets
• skies
• fiducials

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6dF Robot
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Prism, ferrule and optical fibre
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6dF movie
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Observing and overheads

• Observing
• Need approximately two hours per field
  (1.5 on sky plus overheads)
• Two field plates used alternately to minimise
  down-time
• Overheads
• Swapping over the field plates
• Taking flat-field and arc exposures (needed for
  processing and calibrating the object spectra)
• Acquiring target field with telescope

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The Optical Path

• Prism on fibre button
• Optical fibre cable feeds bench-mounted Schmidt
  spectrograph
• 150 fibres line up to form spectrograph slit
• Gratings reflection ? transmission (Sept 2002)
• R covers 5500-8500 Å
• V covers 4000-5600 Å
• 1k x 1k pixel CCD detector

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The 6dF Spectrograph
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(No Transcript)
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Spectra on the CCD

OI sky emission at 5577Å
OH sky emission bands
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Arc Spectrum
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A 6dF Galaxy Spectrum
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Wavelength-Calibrated Galaxy Spectrum

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What is redshift? z Dl/l0

• z 600 Å /6562.82 Å 0.09

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Redshift by Cross-Correlation

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6dFGS Online Database
DR2
http//www-wfau.roe.ac.uk/6dFGS/

• Searchable using either SQL query commands or a
  WWW form
• Each source has its own multi-extension FITS
  file, including 6dF spectrum, brJHK imaging,
  redshift and photometric information

• Image courtesy Heath Jones

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Full Redshift Map

• 50426 6dFGS redshifts
• 19570 ZCAT redshifts
• (Huchra et al 1999)
• 8444 2dFGRS redshifts
• (Colless et al 2001)
• TOTAL 78440 redshifts

• Plot courtesy Heath Jones

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Declination discs10o each

• Plots courtesy Heath Jones

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Visualisation

• Tony Fairall (University of Capetown) is
  developing 3D visualisation software for
  displaying and studying this large-scale
  structure

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Science

• 3D positions and radial velocity give kinematics
  of galaxies, clusters, superclusters
• New quasars being discovered in 6dFGS
• Finding properties of AGN (reddening due to
  obscuration) in conjunction with 2MASS survey
• Radio data helps correlate bulge mass to black
  hole activity in giant elliptical galaxies
• Large-scale structure helps determine
  cosmological parameters
• and more

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• 6dFGS Home http//www.aao.gov.au/local/www/
  6df/
• 6dFGS Database
• http//www-wfau.roe.ac.uk/6dFGS/