Induced Starbursts in Mergers (Invited paper)

Summary

ABSTRACT

Galaxy-galaxy collisions induce nuclear and extranuclear starbursts. The sudden reduction of angular momentum of the interstellar medium due to the gravitational impact of the encounter leads to the subsequent infall to the central regions of a large fraction of the overall interstellar gas. Starburst galaxies with bolometric luminosities ≥ 10¹¹ L⊙ have converted most of the H I into H₂ reaching extreme nuclear densities of molecular gas. We also discuss extranuclear starbursts in relation to the formation of dwarf galaxies in mergers. As a consequence of tidal interactions a fraction of the less gravitationally bound atomic hydrogen that populates the outskirsts of the pre-encounter disk galaxies may escape into intergalactic space. We find that the ejected gas may assemble again and collapse, leading to the formation of intergalactic starbursts, namely, tidal dwarf galaxies.

“STARBURST GALAXIES”

“Starburst” denotes star formation at higher rates than in normally, self-regulated processes. They are non-equilibrium episodes that last only a small fraction of the total life-time of the host stellar systems. “Starburst galaxies” are stellar systems where the overall energy output is dominated by recently formed stars. In the context of this definition we must distinguish the “extragalactic H II regions” (Searle and Sargent, 1972) from the “nuclear starburst galaxies” (Weedman et al. 1981). The first are small, irregular, and dust-poor galaxies where the starburst is encompassing most of the visible galaxy; the second are massive luminous galaxies where the most violent starburst takes place embedded in dust in the central regions.