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Published March 11, 2015 | Published + Submitted
Journal Article Open

C-Band All-Sky Survey: a first look at the Galaxy


We present an analysis of the diffuse emission at 5 GHz in the first quadrant of the Galactic plane using two months of preliminary intensity data taken with the C-Band All-Sky Survey (C-BASS) northern instrument at the Owens Valley Radio Observatory, California. Combining C-BASS maps with ancillary data to make temperature–temperature plots, we find synchrotron spectral indices of β = −2.65 ± 0.05 between 0.408 and 5 GHz and β = −2.72 ± 0.09 between 1.420 and 5 GHz for −10° < |b| < −4°, 20° < l < 40°. Through the subtraction of a radio recombination line free–free template, we determine the synchrotron spectral index in the Galactic plane (|b| < 4°) to be β = −2.56 ± 0.07 between 0.408 and 5 GHz, with a contribution of 53 ± 8 per cent from free–free emission at 5 GHz. These results are consistent with previous low-frequency measurements in the Galactic plane. By including C-BASS data in spectral fits, we demonstrate the presence of anomalous microwave emission (AME) associated with the H ii complexes W43, W44 and W47 near 30 GHz, at 4.4σ, 3.1σ and 2.5σ, respectively. The CORNISH (Co-Ordinated Radio 'N' Infrared Survey for High mass star formation) VLA 5-GHz source catalogue rules out the possibility that the excess emission detected around 30 GHz may be due to ultracompact H ii regions. Diffuse AME was also identified at a 4σ level within 30° < l < 40°, −2° < b < 2° between 5 and 22.8 GHz.

Additional Information

© 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2015 January 28. Received 2015 January 24; in original form 2014 October 24. The C-BASS project is a collaboration between Caltech/JPL in the US, Oxford and Manchester Universities in the UK, and Rhodes University and the Hartebeesthoek Radio Astronomy Observatory in South Africa. It is funded by the NSF (AST-0607857, AST-1010024, and AST-1212217), the University of Oxford, the Royal Society, and the other participating institutions. We would like to thank Russ Keeney for technical help at OVRO. We thank the Xilinx University Programme for their donation of FPGAs to this project. MI acknowledges studentship funding from an EU Marie-Curie IRG grant (no. 230946) awarded to CD. CD acknowledges an STFC Advanced Fellowship and an ERC Starting Grant (no. 307209). JZ acknowledges support from the European Research Council in the form of a Starting Grant with number 240672. PGF acknowledges support from Leverhulme, STFC, BIPAC and the Oxford Martin School. We thank Andy Strong for helpful discussions. We make use of the IDL astronomy library and HEALPIX (Górski et al. 2005).

Attached Files

Submitted - 1501.06069v1.pdf

Published - MNRAS-2015-Irfan-3572-86.pdf


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August 22, 2023
August 22, 2023