The Hawk-I UDS and GOODS Survey (HUGS)

In the deepest region (which includes most of the Hubble Ultra Deep Field) exposure times exceed 80 hours of integration, yielding a 1-{sigma} magnitude limit per square arcsec of ~=28.0ABmag. The seeing is exceptional and homogeneous across the various pointings, confined to the range 0.38-0.43arcsec. In the UDS field the survey is about one magnitude shallower (to match the correspondingly shallower depth of the CANDELS images) but includes also Y-band band imaging (which, in the UDS, was not provided by the CANDELS WFC3/IR imaging).

In the K-band, with an average exposure time of 13 hours, and seeing in the range 0.37-0.43arcsec, the 1-{sigma} limit per square arcsec in the UDS imaging is ~=27.3ABmag. In the Y-band, with an average exposure time ~=8h, and seeing in the range 0.45-0.5arcsec, the imaging yields a 1-{sigma} limit per square arcsec of ~=28.3ABmag. We show that the HUGS observations are well matched to the depth of the CANDELS WFC3/IR data, since the majority of even the faintest galaxies detected in the CANDELS H-band images are also detected in HUGS.

Finally we present the K-band galaxy number counts produced by combining the HUGS data from the two fields. We show that the slope of the number counts depends sensitively on the assumed distribution of galaxy sizes, with potential impact on the estimated extra-galactic background light.