Reduction
The data reduction of the direct imaging data (filters F220W, F555W and F892N) and the slitless grism (G800L) follow different approaches. At each epoch the direct images in a given filter were combined using multidrizzle and oriented with north up east to the left. Details of the treatment of the images and parameters of multidrizzle are given here. and previews of the images can be found here. On account of the low sensitivity of the HRC in the UV, the F220W image is shallow and contains only a few detectable sources. Whilst the F892N exposure time was longer than for the F555W filter (tabulation of the relative exposure times), the filter is very narrow (150A) so the detection limit is about 2.7mag brighter than F555W. As a result there are very few sources detectable on this image and no obvious single emission line objects in the wavelength range 8840 to 8990A.
The slitless G800L grism images were reduced by extracting the first order spectrum (range 5500 to 10500A) of each object which was detected in the corresponding F555W image. A catalogue of the drizzle combined F555W image was made and used to supply the zero points for the extraction of spectra on the G800L image. The region of each spectrum from each individual G800L image was combiined using the drizzle code and the 1D spectrum formed by box extraction of the drizzled spectrum. The aXe package was used. Details of the combination of the spectra and aXe extraction are given here. Browsable pages of the extracted spectra combined with details of the corresponding direct objects, their positions and magnitudes are available for epoch-1 and epoch-2.
Since the GOODS catalogue of the Chandra Deep Field South for the regions of both epoch-1 and epoch-2 UDF HRC fields is available, and is based on the z magnitude (ACS F850LP filter), it is of interest to use this catalogue to extract spectra of red objects which would not be detectable on the F555W images (i.e. v band dropouts). A catalogue of the GOODS catalogued objects which did not have counterparts in the HRC F555W catalogue was produced and used to drive the extraction of the corresponding G800L spectra. Brief details are available here. The spectra were reduced in an identical way and browsable pages of the spectra are available for epoch-1 and epoch-2.
