Ultra-Deep Imaging at the William Herschel Telescope

Over the past few years, we have therefore used the WHT to produce the deepest ground-based image of the sky which we have called the William Herschel Deep Field (WHDF). With exposures of ~30hrs in U and B, the resulting images reach magnitudes which are comparable to the Hubble Deep Fields (U~27, B~ 28) but covering a five times bigger area of the sky than the two HDFs combined. As well as substantial exposures in the redder optical bands from the WHT, the field has also been imaged in the near-IR with a 30hr exposure in K from the UKIRT IRCAM3, reaching K~23 in a small central sub-area and a 14hr exposure in H from the Calar Alto 3.5-m Omega Prime camera covering the whole 7'×7' area and reaching H~23 (McCracken et al., 2000a, McCracken et al., 2000b). Table 1 summarises the current situation. Figure 1 shows an optical ‘true’ colour image of the WHDF.