The Space Density of Spiral Galaxies as function of their Luminosity,\n Surface Brightness and Scalesize

The local space density of galaxies as a function of their basic structural\nparameters --like luminosity, surface brightness and scalesize-- is still\npoorly known. Our poor knowledge is mainly the result of strong selection\nbiases against low surface brightness and small scalesize galaxies in any\noptically selected sample. We show that in order to correct for selection\nbiases one has to obtain accurate surface photometry and distance estimates for\na large (>~1000) sample of galaxies. We derive bivariate space density\ndistributions in the (scalesize, surface brightness)-plane and the (luminosity,\nscalesize)-plane for a sample of ~1000 local Sb-Sdm spiral galaxies. We present\na parameterization of these bivariate distributions, based on a Schechter type\nluminosity function and a log-normal scalesize distribution at a given\nluminosity. We show how surface brightness limits and (1+z)^4 cosmological\nredshift dimming can influence interpretation of luminosity function\ndeterminations and deep galaxy counts.\n

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