The millennium galaxy catalogue: Exploring the color-concentration bimodality via bulge-disk decomposition

Abstract

We investigate the origin of the galaxy color-concentration bimodality at the bright end of the luminosity function (MB - 5log 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) × 108 h 70 M ⊙ 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) × 108 h 70 M ⊙ 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) × 10-4 h 370 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). © 2009. The American Astronomical Society. All rights reserved.