K-s number counts in the Groth and Coppi fields

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.