The Positive Feedback of Population III Objects on Galaxy Formation

Abstract

We study the formation of molecular hydrogen in cooling gas behind shocks produced during the blow-away process thought to occur in the first collapsed, luminous (Population III) objects in the early universe. We find that for a wide range of physical parameters, the H₂ fraction is f ≈ 6×10⁻³. The H₂ mass produced in such explosions can exceed the amount of relic H₂ destroyed inside the photodissociation region surrounding a given Population III object. We conclude, differently from the suggestion of Haiman et al., that these first objects might have a net positive feedback on subsequent galactic formation. We discuss the effects of radiation and the implications of our results for the soft-UV background.