Influence of a generalized Eddington bias on galaxy counts

Tuorla Observatory, University of Turku, 21500 Piikkiö, Finland e-mail: pekkatee@utu.fi

Received: 31 March 2004
Accepted: 11 May 2004

Abstract

We study the influence of the Eddington bias on measured distributions, in particular counts of galaxies when the accuracy of magnitude measurements is variable, e.g. when it changes towards fainter objects. Numerical experiments using different error laws illustrate the effect on the measured slope, helping one to decide if the variable Eddington bias is important, when the simple analytic correction is no longer valid. Common views on the origin and appearance of the Eddington bias are clarified and its relation to the classical Malmquist bias is briefly discussed. We illustrate the “Eddington shift” approach with the counts of bright galaxies in the LEDA database.