  We present H-band infra-red galaxy data to a 3 sigma limit of H=22.9 and
optical-infra-red colours of galaxies on the William Herschel Deep Field. These
data were taken from a 7'x 7' area observed for 14 hours with the Omega Prime
camera on the 3.5-m Calar Alto telescope. We derive H-band number counts,
colour-magnitude diagrams and colour histograms. We review our Pure Luminosity
Evolution galaxy count models based on the spectral synthesis models of Bruzual
& Charlot. These PLE models give an excellent fit to the our H band count data
to H<22.5 and HDF count data to H<28. However, PLE models with a Salpeter IMF
for early-type galaxies overestimate the average galaxy redshift in K<20 galaxy
redshift surveys. Models that assume a steep x=3 IMF give better agreement
data, although they do show an unobserved peak in B-H and I-H colour
distributions at faint H magnitudes corresponding to z>1 early-type galaxies.
This feature may simply reflect a larger scatter in optical-infra-red colours
than in the B-R colour of early-type galaxies at this redshift. This scatter is
obvious in optical-IR colour-colour diagrams and may be explained by on-going
star-formation in an intermediate sub-population of early-type galaxies. The
numbers of EROs detected are a factor of 2-3 lower than predicted by the
early-type models that assume the Salpeter IMF and in better agreement with
those that assume the x=3 IMF. The tight sequence of early-type galaxies also
shows a sub-class which is simultaneously redder in infrared bands and bluer in
the bluer bands than the classical, passive early-type galaxy; this sub-class
appears at relatively low redshifts and may constitute an intermediate age,
early-type population.
