Post on 14-Jan-2016
Galaxies in the UKIDSS Large Area Survey
Jon Loveday
Anthony Smith
Celine Eminian
University of Sussex
Outline
• UK Infrared Deep Sky Survey overview and status
• Near-IR luminosity function
• Photometric redshifts
• Physical Interpretation of near-IR Colours
• Conclusions/future prospects
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
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
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
UKIDSS survey progress
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
LAS: K<16 Vega (17.9 AB)
SDSS: 5740 deg2
453,349 galaxies with redshifts
LAS-K: 476 deg2
19,105 galaxies to K=16 over 195 deg2
(400,000 over 4000 deg2
by end of 2009)
Multivariate : 1/Vmax method
Vmax
Too faint
Too diffuse
Too faint
Too small
Too bright
Too bright
Too concentrated
Too large
K-Petrosian magnitude
r’-Petrosian magnitude
K-surface brightness
K-radius
z = 0.01 z = 0.3
16,452 galaxies within selection limits
(Mr’, MK, K, RK)
K-band BBD (1/Vmax)(Bivariate Brightness Distribution)
K-band BBD (SWML)
Red core (u-r) > 2.35 (SWML)
Blue core (u-r) < 2.35 (SWML)
K-band luminosity function
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
Photometric RedshiftsCeline Eminian
• Use SDSS ugriz and UKIDSS-LAS YJHK magnitudes in ANNz (Collister & Lahav 2004)
• Network architecture 5:10:10:1 (5 bands) or 9:12:12:1 (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
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
• 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
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Stars: constant SFR; Squares = 3Gyr; Ages 5, 10, 15 Gyr bot-top
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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