Dust-correlated cm wavelength continuum emission from translucent clouds ζ Oph and LDN 1780
Article first published online: 11 APR 2011
© 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS
Monthly Notices of the Royal Astronomical Society
Volume 414, Issue 3, pages 2424–2435, July 2011
How to Cite
Vidal, M., Casassus, S., Dickinson, C., Witt, A. N., Castellanos, P., Davies, R. D., Davis, R. J., Cabrera, G., Cleary, K., Allison, J. R., Bond, J. R., Bronfman, L., Bustos, R., Jones, M. E., Paladini, R., Pearson, T. J., Readhead, A. C. S., Reeves, R., Sievers, J. L. and Taylor, A. C. (2011), Dust-correlated cm wavelength continuum emission from translucent clouds ζ Oph and LDN 1780. Monthly Notices of the Royal Astronomical Society, 414: 2424–2435. doi: 10.1111/j.1365-2966.2011.18562.x
- Issue published online: 21 JUN 2011
- Article first published online: 11 APR 2011
- Accepted 2011 February 17. Received 2011 February 17; in original form 2010 August 11
- radiation mechanisms: general;
- ISM: individual objects: LDN 1780;
- ISM: individual objects: ζ Ophiuchi;
- radio continuum: ISM
The diffuse cm wave IR-correlated signal, the ‘anomalous’ CMB foreground, is thought to arise in the dust in cirrus clouds. We present Cosmic Background Imager (CBI) cm wave data of two translucent clouds, ζ Oph and LDN 1780 with the aim of characterizing the anomalous emission in the translucent cloud environment.
In ζ Oph, the measured brightness at 31 GHz is 2.4σ higher than an extrapolation from 5-GHz measurements assuming a free–free spectrum on 8 arcmin scales. The SED of this cloud on angular scales of 1° is dominated by free–free emission in the cm range. In LDN 1780 we detected a 3σ excess in the SED on angular scales of 1° that can be fitted using a spinning dust model. In this cloud, there is a spatial correlation between the CBI data and IR images, which trace dust. The correlation is better with near-IR templates (IRAS 12 and 25 μm) than with IRAS 100 μm, which suggests a very small grain origin for the emission at 31 GHz.
We calculated the 31-GHz emissivities in both clouds. They are similar and have intermediate values between that of cirrus clouds and dark clouds. Nevertheless, we found an indication of an inverse relationship between emissivity and column density, which further supports the VSGs origin for the cm emission since the proportion of big relative to small grains is smaller in diffuse clouds.