Driving galactic winds with magnetic fields at low and high redshift

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Ulrich P. Steinwandel, Klaus Dolag, Harald Lesch, Andreas Burkert

Although playing a key role for our understanding of the evolution of galaxies, the exact way how observed galactic outflows are driven is still far from being understood and therefore our understanding of associated feedback mechanisms that control the evolution of galaxies is still plagued by many enigmas. In this work we present a simple toy model that can provide insight on how non-axis-symmetric instabilities in galaxies (bars, spiral-arms, warps) can lead to local exponential magnetic field growth by a radial flows beyond the equipartition value by at least two orders of magnitude on a time-scale of a few 100 Myr. Our predictions show that the process can lead to galactic outflows in barred spiral galaxies with a mass loading factor η≈0.1, in agreement with our numerical simulations. Moreover, our outflow mechanism could contribute to an understanding of the large fraction of bared spiral galaxies that show signs of galactic outflows in the CHANG-ES survey. Extending our model shows the importance of such processes in high redshift galaxies by assuming equipartition between magnetic energy and turbulent energy. Simple estimates for the star formation rate (SFR) in our model together with cross-correlated masses from the star-forming main-sequence at redshifts z∼2 allow us to estimate the outflow rate and mass loading factors by non-axis-symmetric instabilities and a subsequent radial inflow dynamo, giving mass loading factors of η≈0.1 for galaxies in the range of M⋆=109−1012 M⊙, in good agreement with recent results of Sinfoni and KMOS3D.


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