The Edinburgh/Durham Southern Galaxy Catalogue: an investigation into the large-scale structure of the Universe
Heydon-Dumbleton, Neil H.
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This thesis describes the construction and application of the Edinburgh/Durham Southern Galaxy Catalogue, which is a database of information on ~ 1-5 million galaxies, covering ~ 2000 deg2 of the South Galactic Cap. This catalogue is based on objective image detection and classification techniques, rather than the visual searches of photographic plates used in previous galaxy catalogues. The raw data for this project are digitised scans of 60 ESO/SERC Atlas plates using the COSMOS high-speed plate measuring machine. The quality controls employed during the production of the ESO/SERCAtlas, ensures that it is deeper and more uniform than set of plates used previously to construct a galaxy catalogue. The COSMOS machine objectively detects and parameterises ~ 2 X 105 images on each photographic plate. Image deblending software has been introduced to ensure the accurate detection and parameterisation of images in the crowded regions of compact clusters.Star-galaxy classification and photometric calibration techniques have been investigated and optimised to reduce and quantify any systematic variations that could introduce spurious structure. A classification algorithm has been used to automatically classify images over the whole range of magnitudes in the survey. Accurate intra-plate photometry is possible for galaxies, because a COSMOS magnitude can be defined which is linearly related to the object magnitude. Inter-plate calibration is carried out using CCD galaxy sequences for every second field in the catalogue. Unlike global calibration techniques used previously, this arrangement of CCD’s prevents propagation of calibration errors. Statistics are given to show that the final catalogue of galaxies will be > 95% complete for bj < 20-0 with < 10% contamination by stars and that the point- to-point variation in galaxy number density, due to the combined residual systematic errors in classification and calibration, is ~ 8%.To date a mosaic of 35 plates covering a contiguous region of 1000 deg2 has been constructed. The large-scale galaxy distribution, seen in maps of this data, is dominated by two large supercluster complexes separated by ~ 15° — 20°. Several filamentary arc structures can also be seen, with clusters distributed along them. The number- magnitude counts derived from this database show significant deviation from a noevolution model at bj > 18-75. The variation in the amplitude of the counts across the survey cannot be accounted for by systematic variations in limiting magnitude and so is probably due large-scale clustering of galaxies. The two-point correlation functions calculated for this 35-plate mosaic confirm a break from power-law, though at larger scales (~ 20h-1 Mpc ) than previously estimated. In the context of current theories of galaxy formation, models involving standard cold dark matter with extra large-scale power would still seem to be excluded.