THE MILLENNIUM GALAXY CATALOGUE: EXPLORING THE COLOR-CONCENTRATION BIMODALITY VIA BULGE-DISK DECOMPOSITION

We investigate the origin of the galaxy color-concentration bimodality at the bright end of the luminosity function (M-B - 5 log h(70) < -18 mag) with regard to the bulge-disk nature of galaxies. Via (two-dimensional) surface brightness profile modeling with GIM2D, we subdivide the local galaxy population in the Millennium Galaxy Catalogue into one-component and two-component systems. We reveal that one-component (elliptical and disk-only) systems define the two peaks of the galaxy color-concentration distribution (with total stellar mass densities of (0.7 +/- 0.1) and (1.3 +/- 0.1) x 10(8) h(70) M-circle dot Mpc(-3), respectively), while two-component systems contribute to both a bridging population and the red, concentrated peak (with total stellar mass densities of (1.1 +/- 0.1) and (1.8 +/- 0.2) x 10(8) h(70) M-circle dot Mpc(-3), respectively). Moreover, luminous, bulge-less, red disks, and disk-less, blue bulges (blue ellipticals) are exceptionally rare (with volume densities of (1.7 +/- 0.3) and (1.1 +/- 0.1) x 10(-4) h(70)(3) Mpc(-3), respectively). Finally, within the two-component population we confirm a previously reported correlation between bulge and disk color (with a mean offset of only <(u - r)(bulge) - (u - r)(disk)> = 0.22 +/- 0.02 mag).