| Abstract: | Anomalous microwave emission (AME) is believed to be due to electric dipole
radiation from small spinning dust grains. The aim of this paper is a
statistical study of the basic properties of AME regions and the environment in
which they emit. We used WMAP and Planck maps, combined with ancillary radio
and IR data, to construct a sample of 98 candidate AME sources, assembling SEDs
for each source using aperture photometry on 1 deg-smoothed maps from 0.408 GHz
up to 3000 GHz. Each spectrum is fitted with a simple model of free-free,
synchrotron (where necessary), cosmic microwave background (CMB), thermal dust,
and spinning dust components. We find that 42 of the 98 sources have
significant >5sigma excess emission at frequencies between 20 and 60 GHz. An
analysis of the potential contribution of optically thick free-free emission
from ultra-compact HII regions, using IR colour criteria, reduces the
significant AME sample to 28 regions. The spectrum of the AME is consistent
with model spectra of spinning dust. Peak frequencies are in the range 20-35
GHz except for the California Nebula (NGC1499), which appears to have a high
spinning dust peak frequency of 50+/-17 GHz. The AME regions tend to be more
spatially extended than regions with little or no AME. The AME intensity is
strongly correlated with the sub-millimetre/IR flux densities and comparable to
previous AME detections in the literature. AME emissivity, defined as the ratio
of AME to dust optical depth, varies by an order of magnitude for the AME
regions. The AME regions tend to be associated with cooler dust in the range
14-22 K and an average emissivity index, beta of +1.8, while the non-AME
regions are typically warmer, at 20-30 K, and have a slightly flatter
emissivity index of +1.7. In agreement with previous studies, the AME
emissivity appears to decrease with increasing column density...(abridged) |
REGISTER
Did you like this article? 
