Free access article

A&A 372, 357-363 (2001)
DOI: 10.1051/0004-6361:20010172

Multicolour observations, inhomogeneity and evolution

C. Hellaby

Department of Mathematics and Applied Mathematics, University of Cape Town, Rondebosch, 7701, South Africa

(Received 31 October 2000 / Accepted 30 January 2001 )

Abstract
We propose a method of testing source evolution theories that is independent of the effects of inhomogeneity, and thus complementary to other studies of evolution. It is suitable for large scale sky surveys, and the new generation of large telescopes. In an earlier paper it was shown that basic cosmological observations -luminosity versus redshift, area distance versus redshift and number counts versus redshift -cannot separate the effects of cosmic inhomogeneity, cosmic evolution and source evolution. We here investigate multicolour observations, and show that by comparing luminosity versus redshift in two or more colours, contraints can be placed on source evolution even if unknown source evolution is present, providing an important test of evolution theories that is complementary to present methods. However, number counts in different colours versus redshift are not useful in separating the effects of source evolution and inhomogeneity.

Key words: large scale structure of Universe -- galaxies: evolution

© ESO 2001

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