C-Band All-Sky Survey: a first look at the Galaxy
Davies, R. D.; Davis, R. J.; Dickinson, C.; Leahy, J. P.; Pearson, T. J.; Sutton, D.; Leitch, E. M.; Readhead, A. C. S.; Zuntz, J.; Jonas, J. L.; Jones, Michael E.; Taylor, Angela C.; Muchovej, S. J. C.; Ferreira, P. G.; Irfan, M. O.; Copley, C.; Holler, C. M.; King, O. G.; Leech, J.; Peel, M. W.; Stevenson, M. A.
United Kingdom, South Africa, Germany, United States
Abstract
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.