KsNumber Counts in the Groth and Coppi Fields

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Abstract
We have used William Herschel Telescope/INGRID Ks images on two high-latitude fields, the Coppi and Groth strips, to obtain galaxy number counts over ~180 arcmin2, to a depth of Ks ~ 21.0. Detection efficiency corrections as a function of object size have been calculated on each pointing. We have used a signal-to-noise threshold in two complementary half-exposure images to remove spurious detections. Our data cover the range from Ks = 14.5 to Ks = 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 γb = 0.54-0.63 for K < 17.5 and a slope γf = 0.25-0.29 for K > 17.5. A total contribution from galaxies to the extragalactic background light (EBL) in the K band of νIν = 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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