Authors:Paul D. Allen, Simon P. Driver, Alister W. Graham, Ewan Cameron, Jochen Liske, Roberto De Propris
Abstract: We have modelled the light distribution in 10,095 galaxies from the Millennium Galaxy Catalogue (MGC), providing publically available structural catalogues for a large, representative sample of galaxies in the local Universe. Three different models were used: (1) a single Sersic function for the whole galaxy; (2) a bulge-disc decomposition model using a de Vaucouleurs' R1/4 bulge plus exponential disc; and (3) a bulge-disc decomposition model using a Sersic R1/n bulge plus exponential disc. Repeat observations for 700 galaxies demonstrate that stable measurements can be obtained for components with half-light radii comparable to, or larger than, the seeing half-width at half maximum. We show that with careful quality control, robust measurements can be obtained for large galaxy samples such as the MGC. We use the catalogues to show that the galaxy colour bimodality is due to the two-component nature of galaxies (i.e. bulges and discs) and not to two distinct galaxy populations. We conclude that understanding galaxy evolution demands the routine bulge-disc decomposition of the giant galaxy population at all redshifts.