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Tidal-tail dwarf galaxies - formation, evolution, and survival

Gerhard Hensler

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  • Gerhard Hensler : from Monday 28 May 2018 from 11H00 to Sunday 11 November 2018 until 12H00

Within the hierarchical structure-formation scenario in cosmology today’s massive galaxies are assumed to form from the accumulation of smaller, gas-rich cosmological “building blocks”. In close encounters of massive galaxies tidal forces extract gas and stars to extended tidal arms. The gas clumps dissipatively to multiple self-gravitating and star-forming fragments which resemble young newly formed dwarf galaxies denoted as Tidal Dwarf Galaxies (TDGs). From the galaxy merger rate and from observable bright TDGs it can be concluded that their production may provide an important contribution to the faint end of the galaxy luminosity function. Due to their different regimes in phase space, TDGs’ low gravitation can merely acquire Cold Dark Matter (CDM) from the massive galaxies and, therefore, not be gravitationally supported by DM halos. Since TDGs experience active star formation, the questions arise, whether TDGs can survive the stellar energy feedback, which TDG fraction dissolves from the major galaxies as free-floating DGs, which falls back to the parent galaxies, and which stay bound on orbits around the mature galaxies. By means of detailed chemo-dynamical simulations of TDGs we follow their evolution from their formation in tidal arms and investigate their survival as well as how and which processes affect their evolution. We also address the fundamental question of their observable identification as TDG survivors, which structural and chemical signatures develop to distinguish tidally formed DM-free DGs from ’classical’ ones. We also find variations of the star formation from very low to significantly higher rates triggered by means of compression caused by gasdynamics and by tides. At high star-formation rates, surprisingly none of the models is disrupted by extreme stellar feedback, while also observed low rates indeed question the formation of a fully populated stellar initial mass function. Model TDGs are studied with respect to their star-formation history, stellar feedback, chemical abundances, and internal kinematics.