On the onset of galactic winds in quiescent star forming galaxies

Service d'Astrophysique, CEA/DSM/DAPNIA/SAp, Centre d'Études de Saclay, L'Orme des Merisiers, 91191 Gif-sur-Yvette Cedex, France e-mail: ydubois@cea.fr

Received: 20 July 2007
Accepted: 1 October 2007

Abstract

Context.The hierarchical model of galaxy formation, despite its many successes, still overpredicts the baryons fraction locked in galaxies as a condensed phase. The efficiency of supernovae feedback, proposed a long time ago as a possible solution for this so-called “overcooling” problem, is still under debate, mainly because modelling supernovae explosions within a turbulent interstellar medium, while capturing realistic large scale flows around the galaxy is a very demanding task.

Aims. Our goal is to study the effect of supernovae feedback on a disc galaxy, taking into account the impact of infalling gas on both the star formation history and the corresponding outflow structure, the apparition of a supernovae-driven wind being highly sensitive to the halo mass, the galaxy spin and the star formation efficiency.

Methods. We model our galaxies as cooling and collapsing NFW spheres. The dark matter component is modelled as a static external potential, while the baryon component is described by the Euler equations using the AMR code RAMSES. Metal-dependent cooling and supernovae-heating are also implemented using state-of-the-art recipes coming from cosmological simulations. We allow for three parameters to vary: the halo circular velocity, the spin parameter and the star formation efficiency.

Results. We found that the ram pressure of infalling material is the key factor limiting the apparition of galactic winds. We obtain a very low feedback efficiency, with supernovae to wind energy conversion factor around one percent, so that only low circular velocity galaxies give rise to strong winds. For massive galaxies, we obtain a galactic fountain, for which we discuss the observational properties.

Conclusions. We conclude that for quiescent isolated galaxies, galactic winds appear only in very low mass systems. Although this can quite efficiently enrich the IGM with metals, they do not carry away enough cold material to solve the overcooling problem.