How non-linear scaling relations unify dwarf and giant elliptical galaxies

TL;DR

This paper demonstrates that dwarf and giant elliptical galaxies can be unified under non-linear scaling relations, showing they form a continuous population with varying structure, challenging the idea of a fundamental difference between them.

Contribution

The authors introduce two linear relations that unify dwarf and bright elliptical galaxies, explaining curved relations and supporting a continuous structural variation across galaxy luminosities.

Findings

Curved <mu>_e - R_e relation derived from linear relations.

Dwarf and giant ellipticals form a continuous population.

Structural properties vary smoothly with galaxy luminosity.

Abstract

Dwarf elliptical galaxies are frequently excluded from bright galaxy samples because they do not follow the same linear relations in diagrams involving effective half light radii R_e or mean effective surface brightnesses <mu>_e. However, using two linear relations which unite dwarf and bright elliptical galaxies we explain how these lead to curved relations when one introduces either the half light radius or the associated surface brightness. In particular, the curved <mu>_e - R_e relation is derived here. This and other previously misunderstood curved relations, once heralded as evidence for a discontinuity between faint and bright elliptical galaxies at M_B ~ -18 mag, actually support the unification of such galaxies as a single population whose structure (i.e. stellar concentration) varies continuously with stellar luminosity and mass.