A closer look at supernovae as seeds for galactic magnetization by Evangelia Ntormousi et al. on Thursday 24 November

Explaining the currently observed magnetic fields in galaxies requires

relatively strong seeding in the early Universe. One theory proposes that

magnetic fields of the order of $\mu$G were expelled by supernova (SN)

explosions after primordial, nG or weaker fields were amplified in stellar

interiors. In this work, we calculate the maximum magnetic energy that can be

injected in the interstellar medium by a stellar cluster of mass $M_{cl}$ based

on what is currently known about stellar magnetism. We consider early-type

stars and adopt either a Salpeter or a top-heavy IMF. For their magnetic

fields, we adopt either a Gaussian or a bimodal distribution. The Gaussian

model assumes that all massive stars are magnetized with $10^3 < \langle B_*

\rangle < 10^4$ G, while the bimodal, consistent with observations of Milky Way

stars, assumes only 5-10 per cent of OB stars have $10^3 < \langle B_* \rangle

< 10^4$ G, while the rest have $10 < \langle B_* \rangle < 10^2$ G. We find

that the maximum magnetic energy that can be injected by a stellar population

is between $10^{-10}-10^{-7}$ times the total SN energy. The highest end of

these estimates is about five orders of magnitude lower than what is usually

employed in cosmological simulations, where about $10^{-2}$ of the SN energy is

injected as magnetic. Pure advection of the stellar magnetic field by SN

explosions is a good candidate for seeding a dynamo, but not enough to

magnetize galaxies. Assuming SNe as main mechanism for galactic magnetization,

the magnetic field cannot exceed an intensity of $10^{-7}$ G in the best-case

scenario for a population of $10^{5}$ solar masses in a superbubble of 300 pc

radius, while more typical values are between $10^{-10}-10^{-9}$~G. Therefore,

other scenarios for galactic magnetization at high redshift need to be

explored.

arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.12355v1