Anomalous Microwave Emission from the H II Region RCW175

Creators: Dickinson, C.; Davies, R. D.; Allison, J. R.; Bond, J. R.; Casassus, S.; Cleary, K.; Davis, R. J.; Jones, M. E.; Mason, B. S.; Myers, S. T.; Pearson, T. J.; Readhead, A. C. S.; Sievers, J. L.; Taylor, A. C.; Todorović, M.; White, G. J.; Wilkinson, P. N.

Abstract

We present evidence for anomalous microwave emission in the RCW175 H II region. Motivated by 33 GHz 13' resolution data from the Very Small Array (VSA), we observed RCW175 at 31 GHz with the Cosmic Background Imager (CBI) at a resolution of 4'. The region consists of two distinct components, G29.0-0.6 and G29.1-0.7, which are detected at high signal-to-noise ratio. The integrated flux density is 5.97 ± 0.30 Jy at 31 GHz, in good agreement with the VSA. The 31 GHz flux density is 3.28 ± 0.38 Jy (8.6σ) above the expected value from optically thin free-free emission based on lower frequency radio data and thermal dust constrained by IRAS and WMAP data. Conventional emission mechanisms such as optically thick emission from ultracompact H II regions cannot easily account for this excess. We interpret the excess as evidence for electric dipole emission from small spinning dust grains, which does provide an adequate fit to the data.

Additional Information

© 2009. The American Astronomical Society. Received 2008 July 24; accepted 2008 September 11; published 2008 December 22. Print publication: Issue 2 (2009 January 10). We thank the anonymous referee for useful comments. This work was supported by the Strategic Alliance for the Implementation of New Technologies (SAINT; see www.astro.caltech.edu/chajnantor/saint/index.html), and we are most grateful to the SAINT partners for their strong support. We gratefully acknowledge support from the Kavli Operating Institute and thank B. Rawn and S. Rawn, Jr. The CBI was supported by NSF grants 9802989, 0098734, and 0206416, and a Royal Society Small Research Grant. We are particularly indebted to the engineers who maintain and operate the CBI: C. Achermann, R. Bustos, C. Jara, N. Oyarace, R. Reeves, M. Shepherd, and C. Verdugo. C.D. thanks Roberta Paladini and Bill Reach for useful discussions. C.D. acknowledges support from the U.S. Planck project, which is funded by the NASA Science Mission Directorate. S.C. acknowledges support from FONDECYT grant 1030805, and from the Chilean Center for Astrophysics FONDAP 15010003. A.T. acknowledges support from Royal Society and STFC research fellowships.

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