Casassus, Simon and Dickinson, Clive and Cleary, Kieran and Paladini, Roberta and Etxaluze, Mireya and Lim, Tanya and White, Glenn J. and Burton, Michael and Indermuehle, Balt and Stahl, Otmar and Roche, Patrick (2008) Centimetre-wave continuum radiation from the ρ Ophiuchi molecular cloud. Monthly Notices of the Royal Astronomical Society, 391 (3). pp. 1075-1090. ISSN 0035-8711 http://resolver.caltech.edu/CaltechAUTHORS:CASmnras08
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The ρ Oph molecular cloud is undergoing intermediate-mass star formation. Ultraviolet 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 ∼10–100 K dust is expected at wavelengths longwards of ∼3 mm. Yet cosmic background imager (CBI) observations reveal that the ρ Oph W photodissociation region is surprisingly bright at centimetre wavelengths. We searched for interpretations consistent with the Wilkinson Microwave Anisotropy Probe radio spectrum, new Infrared Space Observatory-Long Wavelength Spectrograph (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 1 cm 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 SR3. Allowing for VSG depletion can marginally reconcile spinning dust with the data. As an alternative interpretation, we consider the continuum from residual charges in ρ Oph W, where most of carbon should be photoionized by the close binary HD 147889 (B2IV, B3IV). Electron densities of ∼10^2 cm^−3 , or H-nucleus densities nH > 10^6 cm^−3 , are required to interpret ρ Oph W as the C ii Strömgren sphere of HD 147889. However, the observed steep and positive low-frequency spectral index would then imply optically thick emission from an hitherto unobserved ensemble of dense clumps or sheets with a filling factor of ∼10^−4 and nH∼ 10^7 cm^−3 .
|Additional Information:||© 2008 Universidad de Chile. Journal compilation © 2008 RAS. Accepted 2008 September 12. Received 2008 September 10; in original form 2008 July 12. We thank the referee for a thorough reading and useful comments. SC acknowledges partial support from FONDECYT grant 1060827, from the Chilean Center for Astrophysics FONDAP 15010003 and from the Center of Excellence in Astrophysics and Associated Technologies (PFB 06). We gratefully acknowledge the generous support of Maxine and Ronald Linde, Cecil and Sally Drinkward, Barbara and Stanely Rawn, Jr, Fred Kavli and Rochus Vogt. This work was supported by the National Science Foundation under grants AST 00-98734 and AST 02-06416. RP acknowledges the support of a Spitzer Cycle-5 archival proposal grant (PAC.PALADINI–1–JPL.000094). This publication makes use of data products from (i) the Two-Micron All-Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center, funded by the National Aeronautics and Space Administration and the National Science Foundation and (ii) the SHASSA, which is supported by the National Science Foundation. The Mopra radio telescope is part of the Australia Telescope which is funded by the Commonwealth of Australia for operations as a National Facility operated by CSIRO. This research also made use of Montage, funded by the National Aeronautics and Space Administration's Earth Science Technology Office, Computational Technnologies Project, under Cooperative Agreement Number NCC5-626 between NASA and the California Institute of Technology. The code is maintained by the NASA/IPAC Infrared Science Archive. This research has made use of the SIMBAD data base, operated at CDS, Strasbourg, France.|
|Subject Keywords:||radiation mechanisms: general • ISM: clouds • radio continuum: general • radio continuum: ISM • submillimetre|
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|Deposited By:||Archive Administrator|
|Deposited On:||22 Dec 2008 20:46|
|Last Modified:||26 Dec 2012 10:39|
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