Article

Anomalous Microwave Emission from the H II Region RCW175

The Astrophysical Journal (impact factor: 6.02). 12/2008; 690(2):1585. DOI:10.1088/0004-637X/690/2/1585 pp.1585

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.

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Keywords

31 GHz flux density
 
33 GHz 13' resolution data
 
CBI
 
distinct components
 
dust grains
 
expected value
 
good agreement
 
integrated flux density
 
IRAS
 
lower frequency radio data
 
optically thick emission
 
RCW175 H II region
 
signal-to-noise ratio
 
small
 
Small Array
 
thermal dust constrained
 
ultracompact H II regions
 
VSA