Publication: K-s number counts in the Groth and Coppi fields
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2003-09-20
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Univ. Chicago Press
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Abstract
We have used William Herschel Telescope/INGRID K_(s) images on two high-latitude fields, the Coppi and Groth strips, to obtain galaxy number counts over ~ 180 arcmin^(2), to a depth of K_(s) ~ 21:0. Detection efficiency corrections as a function of object size have been calculated on each pointing. We have used a signalto-noise threshold in two complementary half-exposure images to remove spurious detections. Our data cover the range from K_(s) = 14.5 to K_(s) = 21.0, so they are useful for investigating a previously reported change in the number count slope (d log N/dm) at K ~ 17. We find a slope ϒ_(b)= 0:54- 0:63 for K < 17.5 and a slope ϒ_(f)= 0.25-0.29 for K > 17.5. A total contribution from galaxies to the extragalactic background light (EBL) in the K band of νI_(ν)=10.5 nW m^(-2) sr^(-1) has been calculated. This K-band EBL coming from galaxies accounts for only ~50% of the recent measurements of the diffuse EBL. Standard number count models fail to reproduce the observed slope change at K ~ 17.5 unless elliptical and spiral formation is pushed to z<̱̱̰2.
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© 2003. The American Astronomical Society. We thank the referee, Jonathan Gardner, for his comments, which helped improve the manuscript. We acknowledge useful discussions on number counts with Matthew Bershady, David Koo, and James Lowenthal. James Lowenthal, Peter Hammersley, and José Acosta-Pulido gave us invaluable help and insights on NIR image reduction. This research has made use of the HST archive and the MDS online database. The Medium Deep Survey catalog is based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555. The MDS analysis was funded by the HST WFPC2 Team and STScI grants GO2684, GO6951, GO7536, and GO8384 to Richard Griffiths and Kavan Ratnatunga at Carnegie Mellon University.