Planck early results. XX. New light on anomalous microwave emission from spinning dust grains

TL;DR

This study uses Planck data to precisely measure the spectra of anomalous microwave emission from two molecular clouds, confirming spinning dust grains as the primary source and providing new insights into their properties and distribution.

Contribution

It presents the most precise measurements to date of spinning dust emission spectra, revealing detailed spectral features and spatial variations in two well-known AME regions.

Findings

Spinning dust spectra peak between 20-40 GHz.

AME in Perseus is mainly from dense molecular gas.

Extended tail at 50-100 GHz in Rho Ophiuchi suggests additional emission components.

Abstract

Anomalous microwave emission (AME) has been observed by numerous experiments in the frequency range ~10-60 GHz. Using Planck maps and multi-frequency ancillary data, we have constructed spectra for two known AME regions: the Perseus and Rho Ophiuchi molecular clouds. The spectra are well fitted by a combination of free-free radiation, cosmic microwave background, thermal dust, and electric dipole radiation from small spinning dust grains. The spinning dust spectra are the most precisely measured to date, and show the high frequency side clearly for the first time. The spectra have a peak in the range 20-40 GHz and are detected at high significances of 17.1 sigma for Perseus and 8.4 sigma for Rho Ophiuchi. In Perseus, spinning dust in the dense molecular gas can account for most of the AME; the low density atomic gas appears to play a minor role. In Rho Ophiuchi, the ~30 GHz peak is dominated by dense molecular gas, but there is an indication of an extended tail at frequencies 50-100 GHz, which can be accounted for by irradiated low density atomic gas. The dust parameters are consistent with those derived from other measurements. We have also searched the Planck map at 28.5 GHz for candidate AME regions, by subtracting a simple model of the synchrotron, free-free, and thermal dust. We present spectra for two of the candidates; S140 and S235 are bright HII regions that show evidence for AME, and are well fitted by spinning dust models.