Tidal dwarf galaxies (TDGs) are kinematically decoupled structures within the expelled tidal arms of interacting galaxies. While they are comparable in size and mass to classical dwarf galaxies, their origin and evolutionary paths are very different. The general population of dwarf sized galaxies are supposed to be remnants of the cosmological structure formation process in the universe, where baryons condensate first in small dark matter (DM) halos which merge and form larger objects later on. Classical dwarf galaxies share a rather isolated self-enriched metallicity history as well as a dominating DM content.

TDGs stem from material which has been pre-enriched while it was still embedded in a large gas-rich disk galaxy. Furthermore, even if the progenitor galaxies are accompanied by dark matter halos, TDGs are not massive enough to bind a significant part of the disturbed DM and are therefore considered to be DM-free objects. Observations show detailed analysis of TDG candidates in the arms of galaxies, confirming the bound structure as well as active star formation.

We are interested in the evolution of TDGs after they have detached from the tidal arm. Numerical

simulations are performed to test the survival of these initially bound structures. In our simulations we include star formation and stellar feedback together with the metal enrichment of both the interstellar gas as well as the stellar component to trace the metallicity history of TDGs. We investigate whether and under which circumstances a TDG can survive the energy impacts of SNIa and SNII explosions, since they have low masses and are not stabilised by a dark matter potential. In addition to intrinsic processes, TDGs are exposed to a possible orbital decay and a shearing tidal field since they are not isolated objects but on eccentric orbits around the combined potential of their parent galaxies.

Statistical considerations have shown that around 10% of the dwarf galaxies in the local universe can origin from a tidal interaction. This number is highly sensitive to the survival rate of TDGs. We aim at examining how the survived TDGs appear in terms of stellar population, chemical composition, physical extent and mass, or gas fraction to provide a more detailed study on a potential survival rate. In the same way our simulations will help to distinguish which observed dwarf galaxies arise from tidal interactions.

Figure 2:

The animation shows the evolution for 262 Myr where the camera is moving around the TDG almost 360 degrees in this time. Orientation is possible with the coordinate triad in the lower left corner of every plot. The TDG is roughly moving in (-x, +y) direction and the external host galaxy is located at a distance of initially 123 kpc and 143 kpc after 262 Myr.

Upper left:
Gas density: Only the 10^-26 g cm^-3 contour is shown

Upper right:
Stellar particles: Only the ones which are already a full stellar population, therefore more than 15 Myr old or at least one star in the most massive star IMF bin.

Lower left:
Temperature: A few smaller SNe explosions are visible and the big superbubble at the very end (also nicely seen in the density contours)

Lower Right:
Gas metallicity: Supernovae explosions release metals in their very low-density bubbles, mixing with the higher density - lower metallicity gas surrounding the bubble reduces it again.