galaxies in the ukidss large area survey

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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are needed to see this picture.

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)



SDSS Main



SDSS Main + UKIDSS



SDSS Main + LRGs



SDSS Main + LRGs

+ UKIDSS



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

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?



Comparsion with BC03



Stars: constant SFR; Squares = 3Gyr; Ages 5, 10, 15 Gyr bot-top

Comparsion with CB07 (prelim)



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 …

galaxies in the ukidss large area survey

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