Relaxing the Bounds on Primordial Magnetic Seed Fields

Abstract

We point out that the lower bound on the primordial magnetic field required to seed the galactic dynamo is significantly relaxed in an open universe or in a universe with a positive cosmological constant. It is shown that, for reasonable cosmological parameters, primordial seed fields of strength 10^{-30} Gauss or less at the time of galaxy formation could explain observed galactic magnetic fields. As a consequence, mechanisms of primordial magnetic seed-field generation that have previously been ruled out could well be viable. We also comment on the implications of the observation of micro-Gauss magnetic fields in galaxies at high redshift.

Figures (3)

• Figure 1: Lower bound on the seed field at galaxy formation $B_{\rm gf}$ vs $\Omega_0$: (a) universe with $\Lambda=0$, (b) flat $\Lambda$ universe.
• Figure 2: Lower bound on the seed field at radiation decoupling $B_{\rm dec}$ vs $\Omega_0$: (a) universe with $\Lambda=0$, (b) flat $\Lambda$ universe.
• Figure 3: Lower bound on $B_{\rm dec}$ vs $\Omega_0$ for generating a field strength of $10^{-6}$ G at redshift $z=0.395$ by the dynamo mechanism in a universe with $\lambda_0+\Omega_0=1$.