Review to be published in "Tidal effects in Astronomy and Astrophysics", Lecture Notes in Physics.
astro-ph/1112.1922

For a PDF version of the article, click here.

TIDES IN COLLIDING GALAXIES


Pierre-Alain Duc 1 and Florent Renaud 2


1 AIM Paris-Saclay, CNRS/INSU, CEA/Irfu, Université Paris-Diderot, Service d'astrophysique, Orme des Merisiers, 91191 Gif sur Yvette cedex, France; paduc@cea.fr
2 Observatoire de Strasbourg, CNRS UMR 7550 and AIM Paris-Saclay, CEA/Irfu, CNRS/INSU, Université Paris-Diderot, Service d'astrophysique, Orme des Merisiers, 91191 Gif sur Yvette cedex, France; florent.renaud@cea.fr


Abstract: Long tails and streams of stars are the most noticeable upshots of galaxy collisions. Their origin as gravitational, tidal, disturbances has however been recognized only less than fifty years ago and more than ten years after their first observations. This Review describes how the idea of galactic tides emerged, in particular thanks to the advances in numerical simulations, from the first ones that included tens of particles to the most sophisticated ones with tens of millions of them and state-of-the-art hydrodynamical prescriptions. Theoretical aspects pertaining to the formation of tidal tails are then presented. The third part of the review turns to observations and underlines the need for collecting deep multi-wavelength data to tackle the variety of physical processes exhibited by collisional debris. Tidal tails are not just stellar structures, but turn out to contain all the components usually found in galactic disks, in particular atomic / molecular gas and dust. They host star-forming complexes and are able to form star-clusters or even second-generation dwarf galaxies. The final part of the review discusses what tidal tails can tell us (or not) about the structure and content of present-day galaxies, including their dark components, and explains how tidal tails may be used to probe the past evolution of galaxies and their mass assembly history. On-going deep wide-field surveys disclose many new low-surface brightness structures in the nearby Universe, offering great opportunities for attempting galactic archeology with tidal tails.


Table of Contents

PRELIMINARY REMARKS

HISTORICAL CONTEXT
Discovery of peculiarities
A controversial scenario
Tidal origin
Forty years of numerical simulations

THEORY OF THE TIDAL TAIL FORMATION IN INTERACTING GALAXIES
Gravitational potential and tidal tensor
Compressive tides
Formation of tidal tails and bridges
Gas dynamics
Influence of the internal and orbital parameters
Spin-orbit coupling
Mass ratio
Impact parameter
Dark matter halo
Rings, ripples, shells and warps
Differences with tides at other scales

MULTI-WAVELENGTH OBSERVATIONS OF TIDAL TAILS
Where the mass is: atomic hydrogen in tidal tails
When components are missing: H i without optical counterparts; stellar tails without gas
Sparse components: molecular clouds, dust and heavy elements

STRUCTURE FORMATION IN TIDAL TAILS
Star formation
Star cluster formation
Formation of Tidal Dwarf Galaxies

TIDAL STRUCTURES AS PROBES OF GALAXY EVOLUTION
Determining the merger rate evolution with tidal tails
Determining the mass assembly history of galaxies with tidal tails
Constraining the distribution of dark matter with tidal tails

CONCLUSIONS

REFERENCES

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