Gerhard Hensler University of Vienna Sylvia Ploeckinger, Simone Recchi (Vienna) Pavel Kroupa (Bonn), Marcel Pawlowski (Cleveland) Mirabel et al. (1992)‏ NGC 3038/39 „Antenna‏Galaxies“ • Merger in an early stadium • TDG candidates are self-gravitating gas clumps in the southern tidal arm In addition, ca. 800-8000 stellar clusters identified comprising 4 populations:  very young:‏≈‏10 Myr  young:‏≈‏100 Myr  ≈‏500 Myr  old:‏≈10 Gyr What is a tidal dwarf galaxy?  At first, observed as HII regions in tidal arms of merging galaxies: star formation!  Gas condensations in the tidal arms.  Gas from outermost galactic regions.  Masses of dwarf galaxies.  Gravitationally bound objects!  Containing old stellar pop.s? probably!  Containing DM? probably not! bright star-formation knots are even structured within the tidal tail. AM 1353-272 (Dentist's chair)‏ Questions:  How many clumps are formed?  How many evolve to TDGs?  How many TDGs survive? Weilbacher et al. (2000)‏ Formation of tidal galaxies Only with combined N-body + SPH sim.s bound structures can form irrespective of the resolution of the simulation. Wetzstein et al. (2007)‏ (2006, A&A, 456) Issues:  Only 2 self-gravitating fragments survive 800 Myrs  Probably none of them will survive 10 Gyrs!? Survival of TDGs? Issues:  The innermost TDGs fall back to the parent merger!  Most of the survivor TDGs form at the tip of the tails!  But: The contribution of TDGs to the total population of dwarf galaxies should be Bournaud & Duc (2006)‏ minor (10% at most)‏