2009ApJ...699..105C

We investigate the origin of the galaxy color-concentration bimodality at the bright end of the luminosity function (M_B- 5log h₇₀< -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)x10⁸ h₇₀M_☉/Mpc3, 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)x10⁸ h₇₀M_☉/Mpc3, 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)x10^–4 h ³₇₀/Mpc3, 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).