Galaxies in the UKIDSS Large Area Survey

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Galaxies in the UKIDSS Large Area Survey

• Jon Loveday
• Anthony Smith
• Celine Eminian
• University of Sussex

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Outline

• UK Infrared Deep Sky Survey overview and status
• Near-IR luminosity function
• Photometric redshifts
• Physical Interpretation of near-IR Colours
• Conclusions/future prospects

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Goals

• Large-scale clustering to z 0.6 (BAO, neutrino
  mass)
• Evolution of galaxy properties (LF, SFR) and
  clustering since z 0.6
• Try out techniques on real data before future
  surveys such as DES, PanSTARRS, LSST etc begin

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UKIDSS

• UK Infrared Deep Sky Survey
• UKIRT 3.8m telescope plus WFCAM (4x20482
  Hawaii-II arrays, 0.21 deg2)
• Étendue of 2.38 m2 deg2 largest of any IR camera
  until VISTA
• zYJHK (1 2.5 ?) near-IR filters
• 5 surveys, 3 extragalactic
• Significantly deeper than 2MASS

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UKIDSS

• Observing started May 2005
• 7 year observing plan (50 of UKIRT time)
• Pipeline processing in Cambridge, archive in
  Edinburgh
• No consortium proprietary data period
• Data immediately available to ESO members once
  verified
• Rest of world 18 months later

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UKIDSS Surveys
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Comparison with 2MASS
Lawrence et al 2007
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UKIDSS survey progress
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Near-IR Luminosity Function(Smith, Cross,
Loveday, in prep)

• UKIDSS-LAS DR2 K-band photometry SDSS DR5
  redshifts
• Need to allow for selection effects in
• r-band flux (SDSS spectro limit)
• K-band flux (UKIDSS completeness limit)
• UKIDSS angular size
• Surface brightness

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LAS Klt16 Vega (17.9 AB)
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SDSS 5740 deg2453,349 galaxies with
redshifts LAS-K 476 deg2
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19,105 galaxies to K16 over 195 deg2 (400,000
over 4000 deg2by end of 2009)
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Multivariate ? 1/Vmax method
16,452 galaxies within selection limits
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K-band BBD (1/Vmax)
(Bivariate Brightness Distribution)
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K-band BBD (SWML)
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Red core (u-r) gt 2.35 (SWML)
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Blue core (u-r) lt 2.35 (SWML)
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K-band luminosity function
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LF Summary

• UKIDSS K-band LF broadly consistent with previous
  results
• Some discrepancies between 1/Vmax and SWML
  estimates
• Low-luminosity discrepancy partly due to
  large-scale structure?
• UKIDSS will be competitive with 2MASS in terms of
  volume/galaxy numbers with DR3 onwards (expected
  December 2007)
• Extend analysis to DXS, UDS and VISTA surveys
  with photo-z to probe evolution

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Photometric RedshiftsCeline Eminian

• Use SDSS ugriz and UKIDSS-LAS YJHK magnitudes in
  ANNz (Collister Lahav 2004)
• Network architecture 510101 (5 bands) or
  912121 (9 bands)
• Committee of five networks
• For each sample, use SDSS spectroscopy
• 3/8 for training
• 1/8 for verification
• 1/2 for testing (numbers shown on plots)

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SDSS Main
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SDSS Main UKIDSS
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SDSS Main LRGs
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SDSS Main LRGs UKIDSS
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SDSS Main Adding near-IR photometry helps to
reduce outliers
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Photo-z Summary

• At low redshifts (z 0.6) addition of near-IR
  photometry helps to improve errors by reducing
  outliers
• Lack of improvement for LRGs with UKIDSS data due
  to
• Small training set cf. network size?
• Uniformity of LRG SED?
• Severe lack of spectroscopic training data for
  ordinary galaxies at redshifts between 0.2 and 1
• Cannot use LRG-trained network to predict
  redshifts of non-LRGs
• AAOmega service proposal in queue to obtain
  spectroscopic redshifts of wide range of
  galaxies out to z 0.6 from coadded data in
  SDSS southern stripe

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Physical Interpretation of near-IR Colours

• Eminian et al, 2007, MNRAS in press
• Compare 3-arcsec aperture photometry from SDSS
  and UKIDSS-LAS with physical galaxy properties
  deduced from SDSS spectra (SDSS-MPA database
  Brinchmann et al 2004) and with stellar
  population synthesis models
• Pair matching technique to remove correlations
  with mass, redshift and concentration

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• Increasing star-formation rate correlates with
  bluer optical colours but redder near-IR colours
  
• Due to dominance of TP-AGB stars in HK bands
  (Marraston 2005)
• These stars also responsible for correlation of
  HK with dust?

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Comparsion with BC03
Stars constant SFR Squares ? 3Gyr Ages 5,
10, 15 Gyr bot-top
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Comparsion with CB07 (prelim)
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Conclusions/Future Prospects

• Goal is to measure evolution in stellar mass and
  clustering of a wide range of galaxy masses to z
  0.6
• Well-calibrated photometric redshifts of
  representative galaxies will be vital to do this
• UKIDSS DR3 (December 2007) will probe volume
  competitive with 2MASS and provide far cleaner
  window function for clustering statistics
• Immediate goal how well can large-scale
  clustering be measured using photo-z (eg. w(?) in
  photo-z slices) compared with using spectroscopic
  redshifts?
• Techniques can then be applied to UKIDSS DXS
  UDS, VISTA

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