Hubble Deep Field South

Coordinates: 22h 32m 56.22s, −60° 33′ 02.69″ Coordinates: 22h 32m 56.22s, −60° 33′ 02.69″ 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). 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. 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″. 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. However the field is closer to the galactic plane than the HDF-N, meaning that it contains more galactic stars. It also has a nearby bright star, as well as a moderately strong radio source close by, but in both cases it was decided that these wouldn't compromise follow-up observations. As with the HDF-N, the field lies in Hubble's Continuous Viewing Zone (CVZ), this time in the south, allowing twice the normal observing time per orbit. At specific times of year, the HST can observe this zone continuously, without it being eclipsed by the Earth. Viewing this field, however, has some issues due to passages through the South Atlantic Anomaly and also with scattered earthshine during daylight hours; the latter can be avoided by using instruments with larger sources of noise, for example from the CCD reading process, at those times. The survey again used Director's Discretionary Time. The field was imaged briefly on October 30–31, 1997 to make sure that the guide stars in the field were acceptable; these guide stars would be required to keep the HST accurately pointing on the region during the observations proper. 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. The observations were made over 10 days in September and October 1998, a total of 150 orbits, and had a total exposure time of over 1.3 million seconds. While the WFPC2 took very deep optical images, the fields were simultaneously imaged by the Space Telescope Imaging Spectrograph (STIS) and the Near Infrared Camera and Multi-Object Spectrometer (NICMOS). A number of flanking fields were also observed for shorter periods of time. The WFPC2 image is 5.3 square arcminutes, whilst the NICMOS and STIS images are only 0.7 square arcminutes. As with the HDF-N, the images were processed using a technique known as 'drizzling', in which the direction the telescope was aimed 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. Translational changes were fine during the imaging parts of the observation; however, the telescope had to be rotated by small amounts instead of repointed during the spectroscopic work, such that the centre of the STIS instrument was kept on the central quasar. The HDF-S final image had a pixel scale of 0.0398 arcseconds.