Centimeter-wave continuum radiation from the rho Ophiuchi molecular cloud
arXiv:0809.3965 · doi:10.1111/j.1365-2966.2008.13954.x
Abstract
The rho Oph molecular cloud is undergoing intermediate-mass star formation. UV radiation from its hottest young stars heats and dissociates exposed layers, but does not ionize hydrogen. Only faint radiation from the Rayleigh-Jeans tail of ~10-100K dust is expected at wavelengths longwards of 3mm. Yet Cosmic Background Imager (CBI) observations reveal that the rho Oph W photo-dissociation region (PDR) is surprisingly bright at centimetre wavelengths. We searched for interpretations consistent with the WMAP radio spectrum, new ISO-LWS parallel mode images and archival Spitzer data. Dust-related emission mechanisms at 1 cm, as proposed by Draine & Lazarian, are a possibility. But a magnetic enhancement of the grain opacity at 1cm is inconsistent with the morphology of the dust column maps Nd and the lack of detected polarization. Spinning dust, or electric-dipole radiation from spinning very small grains (VSGs), comfortably explains the radio spectrum, although not the conspicuous absence from the CBI data of the infrared circumstellar nebulae around the B-type stars S1 and SR~3. Allowing for VSG depletion can marginally reconcile spinning dust with the data. As an alternative interpretation we consider the continuum from residual charges in rho Oph W, where most of carbon should be photoionised by the close binary HD147889 (B2IV, B3IV). Electron densities of ~100 cm^{-3}, or H-nucleus densities n_H > 1E6 cm^{-3}, are required to interpret rho Oph W as the CII Stromgren sphere of HD147889. However the observed steep and positive low-frequency spectral index would then require optically thick emission from an hitherto unobserved ensemble of dense clumps or sheets with a filling factor ~1E-4 and n_H ~ 1E7 cm^{-3}.
accepted for publication in MNRAS
References in corpus (11)
- Infrared Emission from Interstellar Dust. IV. The Silicate-Graphite-PAH Model in the Post-Spitzer Era
- Three-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Temperature Analysis
- A Grid of NLTE Line-Blanketed Model Atmospheres of Early B-type Stars
- The COMPLETE Survey of Star-Forming Regions: Phase I Data
- Bolocam Survey for 1.1 mm Dust Continuum Emission in the c2d Legacy Clouds. II. Ophiuchus
- Polarization Observations with the Cosmic Background Imager
- The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds: VII. Ophiuchus Observed with MIPS
- An upper limit on anomalous dust emission at 31 GHz in the diffuse cloud [LPH96]201.663+1.643
- Inverse temperature dependence of the dust submillimeter spectral index
- A centimetre-wave excess over free-free emission in planetary nebulae
- On Predicting the Polarization of Low Frequency Emission by Diffuse Interstellar Dust