Young tidal dwarf galaxies cannot be used to probe dark matter in galaxies

TL;DR

This study shows that young tidal dwarf galaxies are not suitable for testing dark matter theories because their complex, non-virialized kinematics lead to unreliable placements on the baryonic Tully-Fisher diagram.

Contribution

The paper provides high-resolution spectroscopic analysis demonstrating that TDGs are dynamically young and complex, limiting their use in cosmological tests of dark matter.

Findings

Most TDGs are not virialized and show complex kinematics.

Only one TDG is a perturbed rotation disk close to the bTF relation.

TDGs are young, dynamically forming objects, not suitable for dark matter probing.

Abstract

The location of dark-matter free, tidal dwarf galaxies (TDGs) in the baryonic Tully Fisher (bTF) diagram has been used to test cosmological scenarios, leading to various and controversial results. Using new high-resolution 3D spectroscopic data, we re-investigate the morpho-kinematics of these galaxies to verify whether or not they can be used for such a purpose. We find that the three observed TDGs are kinematically not virialized and show complex morphologies and kinematics, leading to considerable uncertainties about their intrinsic rotation velocities and their locations on the bTF. Only one TDG can be identify as a (perturbed) rotation disk that it is indeed a sub-component of NGC5291N and that lies at $<$1$\sigma$ from the local bTF relation. It results that the presently studied TDGs are young, dynamically forming objects, which are not enough virialized to robustly challenge cosmological scenarios.