Data Release 8

The UDS DR8 release is now available from the WFCAM Science Archive. These data represent a major improvement over the previous release (DR5), with more than double the total exposure time. The median depths are given below (AB, 5σ), estimated from the rms between 2-arcsec apertures placed in source free regions.

  J   H   K   
DR5    24.0 23.7 23.9 
DR8    24.9 24.2 24.6 

Seeing and depth maps

Maps showing the variations in depth and seeing are provided below:

  J   H   K   
Depth maps    text,plot text,plot text,plot 
Seeing maps    text,plot text,plot text,plot 

Image Correction

In addition to the usual quality control and optimisation, the DR8 images were corrected to remove a systematic striping effect in the image background. Bright sources create an artificial depression in the background which extends in perpendicular directions within detector sub-quadrants. These problems were corrected using an optimised median filter applied to the final (source-subtracted) image stacks. Further details will be provided shortly, and in the forthcoming UDS data paper (Almaini et al. in prep.). If you wish to revert the images back to their uncorrected state, simply add the following correction images to the relevant data.

J correction map
H correction map
K correction map

Catalogue Extraction

Catalogues were extracted using Sextractor, with detection from the K-band image. The Sextractor parameter file can be found here. The spurious fraction was estimated by comparing the real catalogue with an equivalent extracted from an inverted image, excluding areas that are typically masked-out for science. To the depths quoted above, the spurious fraction was found to be ~0.5%.