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Tidal Dwarf Galaxies: Ghosts from structure formation

Bonn/Bad Honnef: May 25–29, 2009

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The meeting is sponsored by the » Stellar Populations and Dynamics Research Group at the AIfA and the DFG Priority Programme SPP 1177 » "Witnesses of Cosmic History: Formation and evolution of black holes, galaxies and their environment". The meeting is also supported by the European Science Foundation through » ASTROSIM, and by » the German Science Foundation, DFG.

In the early universe, gas-rich galaxy–galaxy encounters were very frequent. Numerical simulations and observations demonstrate that in such encounters gaseous tidal tails formed that fragmented into dwarf-galaxy sized star-forming regions. The formation of such 'tidal-dwarf galaxies' (TDGs) may have been very frequent. This meeting is to address how common such TDGs may be, what they would look like and which properties they would have now. For e-mail contact please use tdgbonn (at)

Conference DVD

You can find a preview of the Conference DVD here.

Scientific Rationale

Secondary structures form when gas-rich galaxies interact: Conservation of angular momentum and energy leads to expanding tidal arms which fragment and form star-clusters to dwarf-galaxy-type objects. The formation of such "tidal dwarf galaxies" (TDGs) is therefore an inherent part of any cosmological structure formation theory, but understanding TDG formation and evolution is both numerically and observationally at the limit of current technology. Given that gas-rich encounters were very frequent during early structure formation, the contribution of TDGs to the dwarf galaxy population may be important. But this scenario crucially depends on the properties of young TDGs and their survival.

Nearby observed strong encounters between gas-rich galaxies show examples of tidal tails that have a dozen star-forming knots with dwarf-galaxy properties, i.e. masses of 10^7-10^9 solar masses and spatial scales of about one to a few kpc. Computational work on gas-rich galaxy–galaxy encounters suggests rapid fragmentation of tidal tails into dwarf-galaxy-sized self-gravitating objects under certain conditions. Detailed modelling of the evolution of TDGs in their host's potential shows that they are not easily destroyed by the host tide, nor do they merge with their host because the dynamical friction time-scales are too long. It has even been suggested that a large fraction of dE galaxies may be TDGs, thereby naturally accounting for the morphology-density relations for both dwarf and giant galaxies in the field, groups of galaxies, and clusters of galaxies, if only one to two long-lived TDGs form per gas-rich encounter.

Studying the physics of star formation in these exotic objects also opens the possibility of casting a new angle at star formation in general. Do stars form in the same way, i.e. in a range of star clusters, as we see them forming in the Milky Way? Is the stellar mass function the same? How does stellar feedback affect the early evolution of the interstellar matter in these dwarfs, and how does the chemical enrichment proceed? Can TDGs be distinguished in any way from traditional dwarfs? Recent observations show young TDGs to have a dark matter component - what is its nature?

This meeting aims at gaining insights into these problems by assembling both numerical and observational experts in the fields of cosmology, galaxy dynamics, and star formation in TDGs and of observational signatures linking presently forming TDGs in the local universe with dwarf galaxies.


Pavel Kroupa (chair), Pierre Alain Duc (co-chair), Andi Burkert, Gerhard Hensler


Holger Baumgardt, Claudia Brüns, Jörg Dabringhausen, Lucia Klarmann, Pavel Kroupa, Andreas Küpper, Michael Marks, Marcel Pawlowski, Jan Pflamm-Altenburg, Ylva Schuberth, Michael Sokaliwska


The TDGBonn meeting will be taking place in the » Physics Centre of Bad Honnef nearby to Bonn. This is a beautiful ambiente on the River Rhine. Conference participants stay in the Physics Centre which also has its own beer cellar. The lecture hall has the capacity of 100 seats.

Arrival and Departure

Please try to arrive at the Physics Centre on May 24th after lunch time. We have May 25th-29th as full days, and the end of the meeting is planned for Friday evening, May 29th with a final dinner. It is possible to stay overnight at the Physics Centre until Saturday, May 30th. We suggest an excursion on Wednesday afternoon, for example a boat trip along the Rhine River with dinner.

We will be asking those registered for arrival and departure times in April, as we have to communicate this to the Physics Centre.


The programme can be downloaded as » pdf.

Maximum poster dimensions: 120 cm (width) x 150 cm (height).


Please register at the URL below. The deadline for registration was February 28th 2009. The registered participants have been asked to confirm participation with choice of accommodation by March 15th.

There will be no conference fee. It is planned that all participants stay at the Physics Centre in Bad Honnef, although hotels are also available in Bad Honnef. There are about 80 beds available at the Physics Centre, some of which are in double rooms. The cost of staying at the Physics Centre is about 55 Euro per night, which includes three meals per day and the coffee breaks. Please try to arrive by May 24th for dinner in the Centre. Please note that those staying in a hotel will have to pay a fee of 40 Euro each day to the Physics Centre for coffee breaks, lunch and dinner.

For enquiries please contact: tdgbonn (at)

Conference photo

Conference photo

Panorama of Bad Honnef and surroundings

Below we have compiled a panorama picture of the Rhine valley between Bad Honnef and Bonn. Move your mouse on the picture and it will start to scroll. Please note, that display problems may occur when using old browsers.


To scroll, please move the mouse over the picture. (Photo: Tobias Westmeier)

Last update: June 14, 2009