Tides or dark matter sub-halos: Which ones are more attractive?

TL;DR

This paper compares the effects of tidal forces and dark matter sub-halos on the stability of tidal dwarf galaxies, suggesting tidal compression can mimic dark matter effects and influence their survivability.

Contribution

It provides an analytical comparison between tidal acceleration and dark matter sub-halo gravitational effects on TDGs, offering insights into their stability and observed dynamics.

Findings

Tidal fields at 100 kpc from a 10^13 Msol host can mimic a 10^9 Msol dark matter sub-halo.

Tidal compression can explain high dynamical masses in some TDGs.

TDGs may contain less unseen matter than previously thought due to tidal effects.

Abstract

Young tidal dwarf galaxies (TDGs) are observed in the tidal debris of gas-rich interacting galaxies. In contrast to what is generally assumed to be the case for isolated dwarf galaxies, TDGs are not embedded in their own dark matter (DM) sub-halo. Hence, they are more sensitive to stellar feedback and could be disrupted on a short time-scale. Detailed numerical and observational studies demonstrate that isolated DM-dominated dwarf galaxies can have lifetimes of more than 10 Gyr. For TDGs that evolve in a tidal field with compressing accelerations equal to the gravitational acceleration within a DM sub-halo typical of an isolated dwarf galaxy, a similar survival time is expected. The tidal acceleration profile depends on the virial mass of the host galaxy and the distance between the TDG and its host. We analytically compare the tidal compression to the gravitational acceleration due to either cuspy or cored DM sub-halos of various virial masses. For example, the tidal field at a distance of 100 kpc to a host halo of 10^13 Msol can be as stabilizing as a 10^9 Msol DM sub-halo. By linking the tidal field to the equivalent gravitational field of a DM sub-halo, we can use existing models of isolated dwarfs to estimate the survivability of TDGs. We show that part of the unexpectedly high dynamical masses inferred from observations of some TDGs can be explained by tidal compression and hence TDGs require to contain less unobservable matter to understand their rotation curves.