A method is developed for calculating integrated magnitudes of faint galaxies using I COSMOS mapping mode measurements of U&STU Schmidt photographs. The intensity calibration is provided by the step filters and the zero point of the magnitude scale is taken from the photoelectric sky brightness at the time of the exposure. Tests carried out on both star and galaxy images are described. The galaxy magnitudes are isophotal, the limiting isophote being about 28 mag arcsec 2. The errors range from ±O O8 at the bright limit of m - 18 to iOm43 at the faint limit of m - 22. The magnitudes from several hundred galaxies calculated from COSMOS mapping measurements are calibrated against the logarithm of the image area obtained from COSMOS coarse measurements. Using this calibration the magnitudes of galaxies in three areas near the south galactic pole are calculated. The total area of the survey is about 11 arcdeg2 and there are some 83,000 galaxies. The limits of the sample are discussed in detail. The log N(m) relation is compared with standard Friedman cosmological models. Some of these models are modified to take account of selection effects. An excess of observed faint galaxies is found which can be attributed to the effects of evolution or inhomogeneity of the universe. The effect of galaxy evolution is investigated assuming that the luminosity decreases linearly with time. The observations can be explained if, on average, the intrinsic luminosity of a galaxy decreases at the rate of about one magnitude per 1010 yr.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:660605 |
| Date | January 1979 |
| Creators | Pickup, G. E. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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