Pseudo-Evolution of Galaxies in LCDM Cosmology

Abstract

Our knowledge about galaxy evolution comes from transforming observed galaxy properties at different redshifts to co-moving physical scales. This transformation depends on using a cosmological model. Here the effects of unintentional mixing of two different cosmological models on the size evolution of galaxies is studied. As a gedanken experiment, a galaxy of fixed proper size and luminosity is moved across different redshifts. The apparent size of this galaxy is then interpreted with a cosmological model presumed by the observer, which is different compared to the cosmology exhibited by the Universe. In such a case, a spurious size evolution of the galaxy is observed. A galaxy behaving according to the R h = ct and Neumann's cosmology, when interpreted with the ΛCDM cosmological model, shows an increase in size by a factor of 1.1 and 1.3 from z = 7.5 to z ≈ 0, respectively. The apparent size of a galaxy in a static Euclidean cosmology, when interpreted in the ΛCDM model, shows a factor of 23.8 increase in size between z = 7.5 to z ≈ 0. This is in close agreement with the observational data with a size increase of a factor of 6.8 between z = 3.2 to z ≈ 0. Furthermore, using the apparent size data, it is shown that the difference between the derived proper sizes in R h = ct, Neumann's and ΛCDM cosmological models are minimal.