The Submm and mm Excess of the SMC: Magnetic Dipole Emission from
  Magnetic Nanoparticles?
  The Small Magellanic Cloud (SMC) has surprisingly strong submm and
mm-wavelength emission that is inconsistent with standard dust models,
including those with emission from spinning dust. Here we show that the
emission from the SMC may be understood if the interstellar dust mixture
includes magnetic nanoparticles, emitting magnetic dipole radiation resulting
from thermal fluctuations in the magnetization. The magnetic grains can be
metallic iron, magnetite Fe3O4, or maghemite gamma-Fe2O3. The required mass of
iron is consistent with elemental abundance constraints. The magnetic dipole
emission is predicted to be polarized orthogonally to the normal electric
dipole radiation if the nanoparticles are inclusions in larger grains. We
speculate that other low-metallicity galaxies may also have a large fraction of
the interstellar Fe in magnetic materials.
