The Submm and mm Excess of the SMC: Magnetic Dipole Emission from Magnetic Nanoparticles?

TL;DR

This paper proposes that magnetic nanoparticles in the interstellar dust of the SMC can explain its excess submm and mm emission through magnetic dipole radiation, aligning with elemental abundance constraints.

Contribution

It introduces magnetic dipole emission from magnetic nanoparticles as a novel explanation for the SMC's submm/mm excess, expanding dust emission models.

Findings

Magnetic nanoparticles can account for the observed excess emission.

The required iron mass is consistent with elemental abundance constraints.

Magnetic dipole emission is predicted to be polarized orthogonally to electric dipole radiation.

Abstract

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.