P1254156808dVXpF - PowerPoint PPT Presentation

Title: P1254156808dVXpF


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The 6dF Galaxy Survey - The Target SamplesWill
SaundersAnglo-Australian Observatory
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Why 6dFGS

• UK Schmidt has huge AO, AAT/2dF or SLOAN
• Galaxy source counts inversely with brightness
• gt same number of accessible targets per unit
  time for given AO
• Schmidt has unique ability to cover whole sky
• So ideal for wide field, shallow samples, in
  particular new wavebands or techniques.
• And also ideal for peculiar velocities.
• 6dF coincides with first imaging and first NIR
  sky surveys - 2MASS, DENIS.
• Ending of photographic era allows large fraction
  of UKST time to go to 6dF

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Instrumental parameters

• 1K x 1K chip - limited by existing spectrograph
• Focus 3-4 pixels fwhm over chip
• few hundred spectral resolution elements
• Rgt1000 resolution desirable for z-survey,
  imperative for Dn-s
• Coverage 3900A-7500A desired - z0 H,K to z0.1
  Ha.
• gt require 2 grating setups per field.
• 3 x 20min 600V 4000A-5600A _at_ 5-6A fwhm
• 3 x 10min 316R 5400A-8400A _at_ 9-12A fwhm
• 40 mins overhead between fields (changing field
  plate, flats and arcs, slewing, acquisition)
• gt max 4-5 frames/night

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Overall survey parameters

• 4 year hard limit for UKST funding (to June
  2005).
• Button size plate scale gt twice over coverage
• 2 x 17,000 deg2 / 25 deg2 1400 fields
• 18 nights x 13 lunations x 4 years x 75 6dFGS x
  50 clear x 4 fields/night 1400 fields
• 1400 fields x 130 targets/field 180,000 spectra
• reserve 10,000 for z-survey reobservation, 10,000
  for Dn-s reobservation gt 160,000 observable
  targets.

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The Ks-selected sample 1

• 2MASS (2 Micron All-Sky Survey) covers whole sky
  in J,H,Ks
• Very shallow, large pixels. Confusion limited in
  Plane.
• Ks ideal place to study Large Scale Structure -
• Old stellar population - constant mass-to-light
  ratio
• Small external extinction
• Small internal extinction
• But need total magnitudes from low S/N data on
  extended objects.

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Kcor magnitudes

• 2MASS gives reliable isophotal magnitudes K20 -
  comparable depth to 2dF for most galaxies.
• can easily determine average surface brightness
  within this isophote µK20.
• 2MASS gives total magnitude Ktot - noisy but OK
  at high latitude
• can use K20 , µK20 simple model to estimate
  total magnitude, compare with Ktot
• Final estimator
• Kcor K20 - min(1.5 e(1.25(µK20 -20)) , 0.5)
• Robust to confusion noise
• Statistical error 0.11m
• Overall systematic error ltlt 0.1m
• Possible biases at 0.05m level vs galaxy profile
• No extinction correction to the correction!

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The Ks-selected sample 2

• Final selection
• Kcor lt 12.75m
• extended sources
• bgt10
• d lt 0
• AV lt 5m (protostellar sources)
• gt 120,000 targets
• Early-type dominated
• Median redshift z0.06
• Tail to z0.18

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The peculiar velocity survey

• Whole new scale of peculiar velocity survey - can
  rewrite rules
• All spectra in principal good enough resolution
  and wavelength coverage for Dn-s
• Limited by S/N, ellipticity, linewidth, redshift,
  spectral type?
• Can reobserve suitable galaxies with marginally
  poor S/N (or alibi)
• Aim for S/N 20/A at MgB
• Photometry from Ks
• May want to set selection criteria at this meeting

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Additional Samples 1

• If covering whole sky, can include smaller
  samples along for the ride, especially if lower
  completeness is required (cf 2dFGRS/ 2dF quasar
  survey).
• Also, small numbers of additional targets in
  other bands can lead to large complete samples,
  useful for eg comparing clustering vs waveband.
• Samples agreed from early planning were
• H,J-selected 2MASS galaxies to make complete
  samples 100,000 in each final limits Hcor lt
  13.0m, Jcor lt 13.75m
• DENIS I,J -selected galaxies to Jkron lt 13.85m,
  Ikron lt 14.85m, for the 35 of of the sky for
  which DENIS data is reduced
• SUPERCOSMOS-selected galaxies with bgt20 to
  rFlt15.6m, bJlt16.75

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Additional Samples 2

• In addition, the AAO made a call for additional
  targets in late 2000. This led to a large number
  of smaller additional samples being included
• All IRAS FSC galaxies with bgt20, S/N gt 6
• ROSAT All Sky Survey quasars with bJlt18.5m
• HI Parkes All Sky Survey galaxies with ambiguous
  optical identification
• 2MASS-selected red AGN candidates with J-Ks gt 2
• Hamburg-ESO objective prism quasar candidates
• Quasar candidates from the VLA NVSS survey
• Sources from the SUMSS survey with bJ lt 18.5m
• 1000 galaxies to complete the Durham/UKST survey,
  1-in-3 to bJ lt 17.5m
• Galaxies in the Shapley supercluster to rFlt16.0m

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ID sample weight total distinct
unique observe 1 2m_K1275 8/7
118648 118642 15724 112827 7 scos_R156
6/2 63059 9140 1099 8225 8
scos_B1675 6/2 65779 9598 8555
8638 126 fsc_b20r19 6/2 22769
10805 9868 9725 113 RASS_final
6/2 3409 2929 2573 2636 3 2m_H1300
6/2 93965 2308 1146 2077 4
2m_J1375 6/2 98593 2537 2265
2283 119 hipass4sig 6/2 1151
823 810 741 78 durukst
6/2 1145 466 463 419 90 shapley
6/2 1328 945 936 851 6
denisI1485 5/2 22907 4846 3165
4119 5 denisJ1385 5/2 22631
2285 2259 1942 116 6df2magnid_b19r18
4/2 2260 2131 2090 1705 129 hes
4/2 3846 3538 3462 2830 130
nvss 4/2 4460 4334 3051
3467 125 sumss 3/2 13172
4514 4514 2708 totals
539122 179841 61980 165194
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