An Analytic Model of Galactic Winds and Mass Outflows

Abstract

Galactic winds and mass outflows are observed both in nearby starburst\ngalaxies and in high-redshift star-forming galaxies. In this paper we develop a\nsimple analytic model to understand the observed superwind phenomenon. Our\nmodel is built upon the model of McKee & Ostriker (1977) for the interstellar\nmedium. It allows one to predict how properties of a superwind, such as wind\nvelocity and mass outflow rate, are related to properties of its star-forming\nhost galaxy, such as size, gas density and star formation rate. The model\npredicts a threshold of star formation rate density for the generation of\nobservable galactic winds. Galaxies with more concentrated star formation\nproduce superwinds with higher velocities. The predicted mass outflow rates are\ncomparable to (or slightly larger than) the corresponding star formation rates.\nWe apply our model to both local starburst galaxies and high-redshift Lyman\nbreak galaxies, and find its predictions to be in good agreement with current\nobservations. Our model is simple, and so can be easily incorporated into\nnumerical simulations and semi-analytical models of galaxy formation.\n