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Published July 2022 | Published + Accepted Version
Journal Article Open

The C-Band All-Sky Survey (C-BASS): Template fitting of diffuse galactic microwave emission in the northern sky


The C-Band All-Sky Survey (C-BASS) has observed the Galaxy at 4.76 GHz with an angular resolution of 0.73∘ full-width half-maximum, and detected Galactic synchrotron emission with high signal-to-noise ratio over the entire northern sky (δ > −15∘). We present the results of a spatial correlation analysis of Galactic foregrounds at mid-to-high (b > 10∘) Galactic latitudes using a preliminary version of the C-BASS intensity map. We jointly fit for synchrotron, dust, and free-free components between 20 and 1000 GHz and look for differences in the Galactic synchrotron spectrum, and the emissivity of anomalous microwave emission (AME) when using either the C-BASS map or the 408MHz all-sky map to trace synchrotron emission. We find marginal evidence for a steepening (⟨Δβ⟩ = −0.06 ± 0.02) of the Galactic synchrotron spectrum at high frequencies resulting in a mean spectral index of ⟨β⟩ = −3.10 ± 0.02 over 4.76−22.8 GHz. Further, we find that the synchrotron emission can be well modelled by a single power-law up to a few tens of GHz. Due to this, we find that the AME emissivity is not sensitive to changing the synchrotron tracer from the 408 MHz map to the 4.76 GHz map. We interpret this as strong evidence for the origin of AME being spinning dust emission.

Additional Information

© 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model). Received: 25 February 2022. Revision received: 25 April 2022. Accepted: 25 April 2022. Published: 05 May 2022. We thank the referee, Unni Fuskeland, for their useful comments and suggestions that have helped to greatly improve the quality of this paper. The C-BASS project (http://cbass.web.ox.ac.uk) is a collaboration between Oxford and Manchester Universities in the UK, the California Institute of Technology in the USA, Rhodes University, UKZN and the South African Radio Observatory in South Africa, and the King Abdulaziz City for Science and Technology (KACST) in Saudi Arabia. It has been supported by the NSF awards AST-0607857, AST-1010024, AST-1212217, and AST-1616227, and NASA award NNX15AF06G, the University of Oxford, the Royal Society, STFC, and the other participating institutions. This research was also supported by the South African Radio Astronomy Observatory, which is a facility of the National Research Foundation, an agency of the Department of Science and Technology. We would like to thank Russ Keeney for technical help at OVRO. SEH, CD, and JPL acknowledge support from the STFC Consolidated Grant (ST/P000649/1). CD thanks the California Institute of Technology for their hospitality and hosting during several extended visits. We make use of the HEALPix package (Górski et al. 2005), IDL astronomy library (Landsman 1993) and Python astropy (Astropy Collaboration et al. 2013, 2018), MATPLOTLIB (Hunter 2007), NUMPY (Harris et al. 2020), HEALPY (Górski et al. 2005; Zonca et al. 2019), EMCEE (Foreman-Mackey et al. 2013), and SCIPY (Virtanen et al. 2020) packages. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. DATA AVAILABILITY. The northern C-BASS intensity and polarization data are not currently available, but will be released following the publication of the upcoming survey paper (Taylor et al., in preparation). Full tables of template fitting coefficients will be made available online upon request.

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August 22, 2023
October 24, 2023