Anomalous Radio Emission from Dust in the Helix

A byproduct of experiments designed to map the CMB is the recent detection ofa new component of foreground Galactic emission. The anomalous foreground at ~10--30 GHz, unexplained by traditional emission mechanisms, correlates with100um dust emission. We report that in the Helix the emission at 31 GHz and100um are well correlated, and exhibit similar features on sky images, whichare absent in H\beta. Upper limits on the 250 GHz continuum emission in theHelix rule out cold grains as candidates for the 31 GHz emission, and providespectroscopic evidence for an excess at 31 GHz over bremsstrahlung. We estimatethat the 100um-correlated radio emission, presumably due to dust, accounts forat least 20% of the 31 GHz emission in the Helix. This result strengthensprevious tentative interpretations of diffuse ISM spectra involving a new dustemission mechanism at radio frequencies. Very small grains have not beendetected in the Helix, which hampers interpreting the new component in terms ofspinning dust. The observed iron depletion in the Helix favors considering theidentity of this new component to be magnetic dipole emission from hotferromagnetic grains. The reduced level of free-free continuum we report alsoimplies an electronic temperature of Te=4600\pm1200K for the free-free emittingmaterial, which is significantly lower than the temperature of 9500\pm500Kinferred from collisionally-excited lines (abridged).Comment: Accepted for publication in Ap