Surface brightness bias in galaxy catalogues; distance effects |
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| Authors: | S Phillipps J I Davies P J Boyce Rh Evans |
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| Institution: | (1) Department of Physics and Astronomy, University of Wales College of Cardiff, UK |
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| Abstract: | We have investigated the apparent variation of the surface brightness distribution of disc galaxies with distance within three different samples 1) a diameter limited sample of ESO catalogue galaxies in the direction of the cluster A3574 in Centaurus, 2) all ESO catalogue disc galaxies with redshifts, and 3) a sample of fainter galaxies from our surveys of the Fornax Cluster area. In each case we find, as predicted for a sample dominated by surface brightness selection effects, that the distribution narrows with distance. Both high and low surface brightness galaxies are underrepresented in galaxy catalogues. Not because they are rare, but because the volume over which they are sampled is considerably smaller than that of their normal surface brightness counterparts. The question of how many galaxies there are in the Universe remains un-answered. In addition, since selection is byapparent surface brightness, the most distant sample (where cosmological dimming becomes important) contains galaxies of higher intrinsic surface brightness than do the nearby samples, again confirming a previous theoretical prediction. The galaxies we observe in the distant Universe are very different to those we observe close by because of observational selection. |
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