Elliptical Galaxies: Detailed Structure, Scaling Relations and Formation

Abstract

The last decade of research on elliptical galaxies has produced a wealth of new information concerning both their detailed structure and their global scaling relations. We review the old and new results about isophote shapes and subcomponents (Sect. 1), scaling relations of global parameters and redshift evolution (Sect. 2), and the ages, metallicities (Sect. 3) and abundance ratios (Sect. 4). Finally, we confront the observations with hierarchical formation scenarios of elliptical galaxies (Sect. 5). The picture emerging from this variety of observational evidence is broadly consistent with the merging scenario of hierarchical structure formation models, but the stellar population properties of ellipticals pose some challanges. The formation of ellipticals must have always involved some dissipation. The gas fraction at the last major merger event presumably has strong influence on their present day properties. Most elliptical galaxies are old systems, but disky ellipticals might be younger than boxy objects and have more extended star formation histories. The small scatter and the redshift variations of the scaling relation are compatible with passive evolution. The high Mg/Fe overabundances of luminous (boxy) ellipticals point to a rapid star formation episode, while low-luminosity objects have values of Mg/Fe nearly solar, allowing for an extended star formation history.