Magnetic field seeding by galactic winds

Abstract

The origin of intergalactic magnetic fields is still a mystery and several scenarios have been proposed so far: among them, primordial phase transitions, structure‐formation shocks and galactic outflows. In this work, we investigate how efficiently galactic winds can provide an intense and widespread ‘seed’ magnetization. This may be used to explain the magnetic fields observed today in clusters of galaxies and in the intergalactic medium (IGM). We use semi‐analytic simulations of magnetized galactic winds coupled to high‐resolution N‐body simulations of structure formation to estimate lower and upper limits for the fraction of the IGM which can be magnetized up to a specified level. We find that galactic winds are able to seed a substantial fraction of the cosmic volume with magnetic fields. Most regions affected by winds have magnetic fields in the range 10−12 < B < 10−8 G, while higher seed fields can be obtained only rarely and in close proximity to wind‐blowing galaxies. These seed fields are sufficiently intense for a moderately efficient turbulent dynamo to amplify them to the observed values. The volume‐filling factor of the magnetized regions strongly depends on the efficiency of winds to load mass from the ambient medium. However, winds never completely fill the whole Universe and pristine gas can be found in cosmic voids and regions unaffected by feedback even at z= 0. This means that, in principle, there might be the possibility to probe the existence of primordial magnetic fields in such regions.

3D model of magnetic fields evolution in dwarf irregular galaxies

“…magnetize the intergalactic medium as predicted by Kronberg et al (1999) and Bertone et al (2006). The performed simulations indicate that the CR-driven dynamo can explain the observed magnetic fields in dwarf irregular galaxies.…”

Numerical Simulations of the Warm-Hot Intergalactic Medium

“…Among them, primordial magnetic fields, jets and radio lobes emerging from radio galaxies (e.g., Hoyle 1969;Chakrabarti et al 1994;Enßlin et al 1997) and galactic winds (e.g., Kronberg et al 1999;Bertone et al 2006). Simulations (Kronberg et al 1999;Kronberg et al 2001;Bertone et al 2006) show that magnetic fields can be efficiently transported into the IGM and fill most of the universe by z = 0. Bertone et al (2006) predict that galactic winds alone could be responsible for IGM magnetic fields of order 10 −6 -10 −2 µG, in agreement with observations.…”

“…Simulations (Kronberg et al 1999;Kronberg et al 2001;Bertone et al 2006) show that magnetic fields can be efficiently transported into the IGM and fill most of the universe by z = 0. Bertone et al (2006) predict that galactic winds alone could be responsible for IGM magnetic fields of order 10 −6 -10 −2 µG, in agreement with observations.…”

Propagation of ultrahigh energy cosmic rays in extragalactic magnetic fields: a view from cosmological simulations

“…In particular, outside of galaxy clusters the predicted strength of extragalactic magnetic fields diverge when different models of magnetic field seeding are considered, i.e. seeding from primordial fields produced during inflation or baryogenesis (e. g. Widrow et al 2011;Subramanian 2015) versus seeding from magnetised galactic winds (e. g. Bertone et al 2006;Donnert et al 2009) and active galactic nuclei (AGNs) (Xu et al 2009). Recent results from the PLANCK collaboration have put an upper limit on the strength of a primordial field at the surface of the last scattering of the order of B0 0.55 − 5.6nG (Ade et al 2015).…”