Polarization Observations of the Anomalous Microwave Emission in the Perseus Molecular Complex with the COSMOSOMAS Experiment

Abstract

The anomalous microwave emission detected in the Perseus molecular complex by Watson et al. has been observed at 11 GHz through dual orthogonal polarizations with the COSMOSOMAS experiment. Stokes U and Q maps were obtained at a resolution of ∼ 0 • .9 for a 30 • ×30 • region including the Perseus molecular complex. A faint polarized emission has been measured; we find Q = −0.2% ± 1.0%, while U = −3.4 +1.8 −1.4 % both at the 95% confidence level with a systematic uncertainty estimated to be lower than 1% determined from tests of the instrumental performance using unpolarized sources in our map as null hypothesis. The resulting total polarization level is Π = 3.4 +1.5 −1.9 %. These are the first constraints on the polarization properties of an anomalous microwave emission source. The low level of polarization seems to indicate that the particles responsible for this emission in the Perseus molecular complex are not significantly aligned in a common direction over the whole region, as a consequence of either a high structural symmetry in the emitting particle or a low-intensity magnetic field. Our weak detection is fully consistent with predictions from electric dipole emission and resonance relaxation at this frequency.

Astronomical Models of PAHs and Dust

“…For the size distribution used to account for the PAH emission features in the infrared results, the predicted rotational emission appears to be in agreement with the observed intensity of dust-correlated microwave emission (e.g., Dobler et al 2009;). There do not appear to be any mechanisms that can effectively align PAH angular momenta with the galactic magnetic field (Lazarian & Draine 2000), and the rotational emission from PAHs is therefore expected to be essentially unpolarized, in agreement with upper limits on the polarization of the dust-correlated microwave emission (Battistelli et al 2006;Mason et al 2009). By contrast, the far-infrared and submm emission from larger grains is expected to have polarizations as large as ∼10% (Draine & Fraisse 2009) -soon to be measured by Planck.…”

Planck2015 results

“…The best constraint comes from the Perseus region, which has significant AME emission and relatively little contaminating synchrotron emission. Battistelli et al (2006) reported a weak detection in Perseus at 3.4 +1.5 −1.9 % at 11 GHz, while later measurements obtained by López-Caraballo et al (2011) using WMAP data found a 2σ limit of <1%; Dickinson et al (2011) have also measured a 2σ limit of <1.4% for Perseus (as well as an upper limit of <1.7% in ρ Ophiuchus), and Génova- Santos et al (2015) found a 2σ limit of <2.8% in Perseus at 19 GHz. Recently, Battistelli et al (2015) have claimed to detect polarized AME emission at 21.5 GHz from RCW 175, an H ii region, where they measured a polarization percentage of (2.2 ± 0.2 (random) ± 0.3 (systematic))% at 21.5 GHz.…”

The pre-launchPlanckSky Model: a model of sky emission at submillimetre to centimetre wavelengths

“…Spinning dust emission is observed to be at most weakly polarised, of order a few percent (Battistelli et al 2006;López-Caraballo et al 2011;Dickinson et al 2011). On the theoretical side, Lazarian & Draine (2000) predict very low (but possibly measurable) levels of polarisation for spinning dust emission.…”