  Based on magnitudes and Petrosian radii from the Sloan Digital Sky Survey
(SDSS, data release 7) at low redhift (z <0.2), we developed a test of
galaxy-size evolution. For this first quantitative size analysis using SDSS
data, several possible sources of systematic errors had to be considered. The
Malmquist bias is excluded by volume-limited samples. A correction for seeing
has been developed and applied. We compare different methods to perform the
K-correction, and avoid selection effects due to different filters. It is found
that apparent average galaxy size slightly decreases with redshift z,
corresponding to a growth in time. The effect is smaller for a lower H0, and at
the same time less pronounced at higher redshifts, but persists in both cases.
Although there is no systematic variation with galaxy luminosity, we took into
account the recently discovered luminosity evolution with redshift. Assuming
this effect of unknown origin to be real, we find a slight increase of galaxy
size with z. The relative change of average size with z usually amounts to less
than one half of the respective increase of wavelengths due to the cosmological
redshift, making a cosmological interpretation difficult. While the effect
shows clear statistical significance, unknown systematics cannot be excluded.
In any case, the enigmatic observations of size and luminosity evolution need
to be analysed together. To facilitate further investigations, a complete
Mathematica code and instructions for data download are provided.
