Correlations between r 1/4 -Law Parameters for Bulges and Elliptical Galaxies

Abstract

The correlation between the effective radius r e and surface brightness μ e for elliptical galaxies is a fundamental scaling law that theories of galaxy formation must explain. When r e and μ e are derived by fitting two-parameter fitting functions such as the de Vaucouleurs r 1/4 law to brightness profiles, the errors in the parameters are strongly coupled. The purpose of this paper is to rederive the μ e (log r e ) relations for ellipticals and bulges, taking account of the coupling in the errors and using only high-accuracy CCD data. Our preliminary conclusions are: (1) The coupled errors are too small to affect significantly the correlation derived for elliptical galaxies. (2) The correlation for bulges is not very different from that for ellipticals, but the galaxy sample is small and the errors in the parameters are large due to the inherent uncertainty in bulge-disk decomposition.