Constraining the anomalous microwave emission mechanism in the S140 star-forming region with spectroscopic observations between 4 and 8 GHz at the Green Bank Telescope

Journal article

Anomalous microwave emission (AME) is a category of Galactic signals that cannot be explained by synchrotron, thermal dust, or optically thin free–free radiation. Spinning dust is one variety of AME that could be partially polarized and is therefore relevant for cosmic microwave background polarization studies. The Planck satellite mission identified candidate AME regions in approximately 1° patches that were found to have spectra generally consistent with spinning dust grain models. The spectra for one of these regions, G107.2+5.2, was also consistent with optically thick free–free emission because of a lack of measurements between 2 and 20 GHz. Follow-up observations were needed. Therefore, we used the C-band receiver and the Versatile Green Bank Telescope (GBT) Astronomical Spectrometer at the GBT to constrain the AME mechanism. For the study described in this paper, we produced three band-averaged maps at 4.575, 5.625, and 6.125 GHz and used aperture photometry to measure the spectral flux density in the region relative to the background. We found that if the spinning dust description is correct, then the spinning dust signal peaks at 30.9 ± 1.4 GHz, and it explains the excess emission. The morphology and spectrum together suggest the spinning dust grains are concentrated near S140, which is a star-forming region inside our chosen photometry aperture. If the AME is sourced by optically thick free–free radiation, then the region would have to contain H ii with an emission measure of ${5.27}_{-1.5}^{+2.5}\times {10}^{8}\,{\mathrm{cm}}^{-6}\,\mathrm{pc}$ and a physical extent of ${1.01}_{-0.20}^{+0.21}\times {10}^{-2}$ pc. This result suggests the H ii would have to be ultra- or hyper-compact to remain an AME candidate.

Authors: Abitbol, M; Johnson, B; Jones, G; Dickinson, C; Harper, S

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Astronomical Society
• Journal: Astrophysical Journal
• Volume: 864
• Issue: 1
• Article number: 97
• Publication date: 2018-09-04
• Acceptance date: 2018-07-19
• DOI: 10.3847/1538-4357/aad548
• EISSN: 1538-4357
• ISSN: 0004-637X
• Keywords: ISM: clouds; radio continuum: ISM; H II regions; radiation mechanisms: general; dust, extinction; cosmic background radiation