Dwarf elliptical galaxies as ancient tidal dwarf galaxies
J\"org Dabringhausen, Pavel Kroupa

TL;DR
This paper reviews the formation, properties, and potential evolutionary paths of tidal dwarf galaxies (TDGs), suggesting they could account for all dwarf ellipticals and challenge current galaxy formation theories.
Contribution
It provides the first comprehensive observational and numerical sample of TDG candidates and discusses their implications for galaxy formation models.
Findings
TDGs are gas-rich and evolve into gas-poor dwarf ellipticals.
Observed gas-poor TDGs resemble normal dwarf ellipticals.
Long-lived TDGs could explain all dwarf ellipticals in the universe.
Abstract
The formation of tidal dwarf galaxies (TDGs) is triggered by the encounters of already existing galaxies. Their existence is predicted from numerical calculations of encountering galaxies and is also well documented with observations. The numerical calculations on the formation of TDGs furthermore predict that TDGs cannot contain significant amounts of non-baryonic dark matter. In this paper, the first exhaustive sample of TDG-candidates from observations and numerical calculations is gathered from the literature. These stellar systems are gas-rich at the present, but they will probably evolve into gas-poor objects that are indistinguishable from old dwarf elliptical galaxies (dEs) based on their masses and radii. Indeed, known gas-poor TDGs appear as normal dEs. According to the currently prevailing cosmological paradigm, there should also be a population of primordial galaxies that…
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