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Resolved spectral variations of the centimetre-wavelength continuum from the ρ Oph W photodissociation region

Casassus, Simon and Vidal, Matías and Arce-Tord, Carla and Dickinson, Clive and White, Glenn J. and Burton, Michael and Indermuehle, Balthasar and Hensley, Brandon (2021) Resolved spectral variations of the centimetre-wavelength continuum from the ρ Oph W photodissociation region. Monthly Notices of the Royal Astronomical Society, 502 (1). pp. 589-600. ISSN 0035-8711. doi:10.1093/mnras/staa4016.

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Centimetre-wavelength radio continuum emission in excess of free–free, synchrotron, and Rayleigh–Jeans dust emission (excess microwave emission, EME), and often called ‘anomalous microwave emission’, is bright in molecular cloud regions exposed to UV radiation, i.e. in photodissociation regions (PDRs). The EME correlates with infrared (IR) dust emission on degree angular scales. Resolved observations of well-studied PDRs are needed to compare the spectral variations of the cm-continuum with tracers of physical conditions and of the dust grain population. The EME is particularly bright in the regions of the ρ Ophiuchi molecular cloud (ρ Oph) that surround the earliest type star in the complex, HD 147889, where the peak signal stems from the filament known as the ρ Oph W PDR. Here, we report on Australia Telescope Compact Array observations of ρ Oph W that resolve the width of the filament. We recover extended emission using a variant of non-parametric image synthesis performed in the sky plane. The multifrequency 17–39 GHz mosaics reveal spectral variations in the centimetre-wavelength continuum. At ∼30 arcsec resolutions, the 17–20 GHz intensities tightly follow the mid-IR, I_(cm) ∝ I(8 μm), despite the breakdown of this correlation on larger scales. However, while the 33–39 GHz filament is parallel to Infrared Array Camera 8 μm, it is offset by 15–20 arcsec towards the UV source. Such morphological differences in frequency reflect spectral variations, which we quantify spectroscopically as a sharp and steepening high-frequency cutoff, interpreted in terms of the spinning dust emission mechanism as a minimum grain size a_(cutoff) ∼ 6±1Å that increases deeper into the PDR.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper ItemSKYMEM package
https://atoa.atnf.csiro.auRelated ItemAustralia Telescope Online Archive
Casassus, Simon0000-0002-0433-9840
Vidal, Matías0000-0003-2134-1587
Arce-Tord, Carla0000-0002-0176-4331
Dickinson, Clive0000-0002-0045-442X
Burton, Michael0000-0001-7289-1998
Hensley, Brandon0000-0001-7449-4638
Alternate Title:Resolved spectral variations of the centimetre-wavelength continuum from the rho Oph W photo-dissociation-region
Additional Information:© 2021 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2020 December 23. Received 2020 December 23; in original form 2020 October 1. Published: 04 January 2021. We thank the referee, Yvette Chanel Perrott, who provided important input for the presentation of the SKYMEM algorithm and for the interpretation of the SED fits, in addition to constructive comments on the analysis and a thorough reading. We also acknowledge interesting discussions and comments from Kieran Cleary, Roberta Paladini, Jacques Le Bourlot, and Evelyne Roueff. SC acknowledges support from a Marie Curie International Incoming Fellowship (REA-236176) and by FONDECYT grant 1171624. MV acknowledges support from FONDECYT through grant 11191205. GJW gratefully thanks the Leverhulme Trust for the award of an Emeritus Fellowship. Data Availability: The SKYMEM package can be found at The corresponding author will provide help to researchers interested in porting SKYMEM to other applications. The SKYMEM code repository also includes, as an example application, the sky-plane version of the data underlying this article. The unprocessed visibility data set can be downloaded from the Australia Telescope Online Archive at The corresponding author will share the calibrated visibility data on reasonable request.
Funding AgencyGrant Number
Marie Curie FellowshipREA-236176
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)1171624
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)11191205
Leverhulme TrustUNSPECIFIED
Subject Keywords:radiation mechanisms: general – ISM: clouds – ISM: individual objects: ρ Oph, Rho Oph W filament, SR4, DoAr21 – photodissociation region – radio continuum: general – submillimetre: ISM
Issue or Number:1
Record Number:CaltechAUTHORS:20210602-102940907
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Official Citation:Simon Casassus, Matías Vidal, Carla Arce-Tord, Clive Dickinson, Glenn J White, Michael Burton, Balthasar Indermuehle, Brandon Hensley, Resolved spectral variations of the centimetre-wavelength continuum from the ρ Oph W photodissociation region, Monthly Notices of the Royal Astronomical Society, Volume 502, Issue 1, March 2021, Pages 589–600,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:109341
Deposited By: Tony Diaz
Deposited On:02 Jun 2021 18:26
Last Modified:02 Jun 2021 18:26

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