Tentative Detection of Electric Dipole Emission from Rapidly Rotating Dust Grains

We present the first tentative detection of spinning dust emission from specific astronomical sources. All other detections in the current literature are statistical. The Green Bank 140 foot telescope was used to observe 10 dust clouds at 5, 8, and 10 GHz. In some cases, the observed emission was consistent with the negative spectral slope expected for free-free emission (thermal bremsstrahlung), but in two cases it was not. One H II region (LPH 201.663+1.643) yields a rising spectrum, inconsistent with free-free or synchrotron emission at the ∼ 10σ level. One dark cloud (L 1622) has a similar spectrum with lower significance. Both spectra are consistent with electric dipole emission from rapidly rotating dust grains (“spinning dust”), as predicted by Draine & Lazarian. Subject headings: cosmic microwave background — diffuse radiation — dust, extinction — ISM: clouds — radiation mechanisms: thermal — radio continuum: ISM and University of California at Berkeley, Department of Astronomy Hubble Fellow