1 Laboratoire de Physique Statistique de l'Ecole Normale Supérieure,
CNRS UMR 8550,
24 Rue Lhomond, 75231 Paris Cedex 05, France
2 DAMTP, University of Cambridge, Centre for Mathematical
Sciences, Wilberforce Road, Cambridge CB3 0WA
3 CEA, Irfu, SAp (UMR AIM), Centre de Saclay, F-91191
Gif-sur-Yvette, France
2 MAG (IPGP/ENS), CNRS UMR 7154, LRA,
Ecole Normale Supérieure, 24 Rue Lhomond, 75231 Paris Cedex 05, France
Accepted 2008 December 23. Received 2008 December 23; in original form 2008 November 4
Abstract. We present kinematic simulations of a galactic dynamo model based on the large-scale differential rotation and the small-scale helical fluctuations due to supernova explosions. We report for the first time direct numerical simulations of the full galactic dynamo using an unparametrized global approach. We argue that the scale of helicity injection is large enough to be directly resolved rather than parametrized. While the actual superbubble characteristics can only be approached, we show that numerical simulations yield magnetic structures which are close to both the observations and the previous parametrized mean field models. In particular, the quadrupolar symmetry and the spiraling properties of the field are reproduced. Moreover, our simulations show that the presence of a vertical inflow plays an essential role to increase the magnetic growth rate. This observation could indicate an important role of the downward flow (possibly linked with galactic fountains) in sustaining galactic magnetic fields.