Computer Science
Scientific paper
Sep 1987
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987phdt........57k&link_type=abstract
Thesis (PH.D.)--UNIVERSITY OF EDINBURGH (UNITED KINGDOM), 1987.Source: Dissertation Abstracts International, Volume: 49-08, Sec
Computer Science
4
Scientific paper
Available from UMI in association with The British Library. Requires signed TDF. An investigation into the selection effects of optical quasar surveys is described. This is accomplished via the accumulation and comparison of optical quasar surveys of different types, which are then used to generate a survey free from selection effects. An automatic search of a deep C.F.H.T. grens plate over 1 degree^2 in the centre of the field was undertaken. Slit spectroscopic observations were made of 26 candidates from this survey. An automatic photometric survey was also undertaken, using direct plates in the five wavebands U, J, V, R, and I from the U.K. Schmidt telescope. CCD frames were obtained in each of the wavebands from various sources, to allow calibration of data from the Schmidt plates. This has allowed the construction of a conventional ultraviolet excess sample, as well as a less conventional colour space density search generated sample. Locating the various low dispersion spectroscopic survey candidates amongst the photometric survey data has brought to light various aspects of these surveys: in particular, the eye discovers a smaller surface density of candidates at most magnitudes. Secondly, the automatic prism plate search has significant progressive object losses brighter than the plate limit, which are subject to complex selection effects. Large numbers of galactic stars are mistaken for quasars because of peculiarities in their spectra seen at low dispersion. Also prism dispersion variations force a survey limit brighter than the plate limit. Colour synthesis from the prism plate works well at brighter magnitudes, unless spectra are saturated. Spectroscopy indicates that the automatic grens survey is complete, except for overlapped spectra. This is in part due to the linear dispersion of the transmission grating. The photometric survey readily identifies objects which have peculiar colours, but a detailed examination of the properties of these objects must await further work. Finally, a synthetic survey has been constructed, using all of the information available for each object. Redshift estimates were possible for about 30% of the 130 candidates --the higher redshift objects. Examination of the survey indicates that it is largely free from selection effects below a redshift of z = 3.4. (Abstract shortened by UMI.).
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