Are "dwarf" Ellipticals genuine Ellipticals?

TL;DR

This paper investigates whether dwarf elliptical galaxies are fundamentally the same as normal ellipticals by analyzing their properties and profiles, finding continuity outside the core and suggesting some dwarf ellipticals are genuine ellipticals.

Contribution

It demonstrates that the properties of dwarf and normal ellipticals vary continuously outside the core, challenging the idea of a strict dichotomy and clarifying the nature of nucleated versus non-nucleated dwarfs.

Findings

Surface brightness profiles vary continuously from dwarf to normal ellipticals.

Nucleated dwarf ellipticals resemble normal ellipticals in clustering and flattening.

Non-nucleated dwarfs may be a different galaxy class.

Abstract

We review the systematic properties of ``dwarf'' elliptical (dE) galaxies, focussing on the relation between ``normal'' and ``dwarf'' ellipticals. In recent years, this relation has been described as ``dichotomy'' -- based essentially on a discontinuity in central surface brightness. We show that, outside of 300 pc from the centre, the S\'ersic profile parameters vary continuously from ``normal'' to ``dwarf'' ellipticals. The ``dichotomy'' is indeed restricted to the very central part, where differences also exist among ``normal'' ellipticals (E). Bright, nucleated dE's closely resemble ``normal'' E's also in their clustering and flattening properties. They may be genuine ellipticals, having no present-day late-type dwarf precursor from which they could have been manufactured. The non-nucleated dE's ("dwarf spheroidals") may be a different breed.