Hubble Deep Field South
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The Hubble Deep Field South is a composite of several hundred individual images taken using the Hubble Space Telescope's Wide Field and Planetary Camera 2 over 10 days in September and October 1998. It followed the great success of the original Hubble Deep Field in facilitating the study of extremely distant galaxies in early stages of their evolution. While the WFPC2 took very deep optical images, nearby fields were simultaneously imaged by the Space Telescope Imaging Spectrograph (STIS) and the Near Infrared Camera and Multi-Object Spectrometer (NICMOS).
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[edit] Planning
The rationale behind making another Deep Field image was to provide observatories in the southern hemisphere with a similarly deep optical image of the distant universe as had been provided to those in the northern hemisphere. As with the original Hubble Deep Field (referred to hereafter as the 'HDF-N'), the target area was selected to be far from the plane of the Milky Way's galactic disk, which contains a large amount of obscuring matter, and to contain as few galactic stars as possible. It lay in the Space Telescope's southern Continuous Viewing Zone (CVZ), which is not occulted by the Earth or Moon as Hubble orbits the Earth. The field chosen was in the constellation of Tucana at a right ascension of 22h 32m 56.22s and declination of -60° 33' 02.69" [1].
The field was imaged briefly in 1997 to determine the locations of guide stars, which would be required to keep the HST accurately pointing on the region during the observations proper.
[edit] Observations
The observing strategy for the HDF-S was similar to that of the HDF-N, with the same optical filters used for the WFPC2 images (isolating wavelengths at 300, 450, 606 and 814 nanometres), and similar total exposure times. As with the HDF-N, the images were processed using a technique known as 'drizzling', in which the telescope pointing was changed by a very small amount between exposures, and the resulting images combined using sophisticated techniques to achieve a higher angular resolution than would otherwise be possible. The HDF-S final image had a pixel scale of 0.0398 arcseconds.
[edit] Contents of the HDF-S
The cosmological principle states that at the largest scales, the universe is homogenous and isotropic, meaning that it should look the same in any direction. The HDF-S would thus be expected to strongly resemble the HDF-N, and this was indeed the case, with large numbers of galaxies visible displaying a similar range of colours and morphologies to those seen in the HDF-N.
One difference with the HDF-N was that the HDF-S included a known quasar with a redshift value of 2.24. This was included in the field to allow simultaneous analysis of galaxies and quasars at similar distances from Earth.
[edit] Scientific results
As with the HDF-N, the HDF-S provided rich pickings for cosmologists. Many studies of the HDF-S confirmed results found from the HDF-N, such as star formation rates over the lifetime of the universe. The HDF-S was also extensively used in studies of how galaxies evolve over time, both due to internal processes and encounters with other galaxies.
