THE CARNEGIE-IRVINE GALAXY SURVEY. III. THE THREE-COMPONENT STRUCTURE OF NEARBY ELLIPTICAL GALAXIES

Motivated by recent developments in our understanding of the formation and evolution of massive galaxies, we explore the detailed photometric structure of a representative sample of 94 bright, nearby elliptical galaxies, using high-quality optical images from the Carnegie-Irvine Galaxy Survey. The sample spans a range of environments and stellar masses, from M-* = 10(10.2) to 10(12.0) M-circle dot . We exploit the unique capabilities of two-dimensional image decomposition to explore the possibility that local elliptical galaxies may contain photometrically distinct substructure that can shed light on their evolutionary history. Compared with the traditional one-dimensional approach, these two-dimensional models are capable of consistently recovering the surface brightness distribution and the systematic radial variation of geometric information at the same time. Contrary to conventional perception, we find that the global light distribution of the majority (greater than or similar to 75%) of elliptical galaxies is not well described by a single Sersic function. Instead, we propose that local elliptical galaxies generically contain three subcomponents: a compact (R-e less than or similar to 1 kpc) inner component with luminosity fraction f approximate to 0.1-0.15; an intermediate-scale (R-e approximate to 2.5 kpc) middle component with f approximate to 0.2-0.25; and a dominant (f = 0.6), extended (R-e approximate to 10 kpc) outer envelope. All subcomponents have average Sersic indices n approximate to 1-2, significantly lower than the values typically obtained from single-component fits. The individual subcomponents follow well-defined photometric scaling relations and the stellarmass-size relation. We discuss the physical nature of the substructures and their implications for the formation of massive elliptical galaxies.