Observations of Galactic star-forming regions with the Cosmic Background Imager at 31 GHz
Studies of the diffuse Galactic radio emission are interesting both for better understanding the physical conditions in our Galaxy and for minimizing the contamination in cosmological measurements. Motivated by this, we present Cosmic Background Imager 31 GHz observations of the Galactic regions NGC 6357, NGC 6334, W51 and W40 at ∼4.5 arcmin resolution and conduct an investigation of the spectral emission process in the regions at 4.5 arcmin and 1° resolution. We find that most of the emission in the regions is due to optically thin free–free. For two sub-regions of NGC 6334 and for a sub-region of W51 though, at 4.5 arcmin resolution and at 31 GHz we detect less emission than expected from extrapolation of radio data at lower frequencies assuming a spectral index of −0.12 for optically thin free–free emission, at 3.3σ, 3.7σ and 6.5σ, respectively. We also detect excess emission in a sub-region of NCG 6334 at 6.4σ, after ruling out any possible contribution from ultra-compact H II regions. At 1° resolution, we detect a spinning dust component in the spectral energy distribution of W40 that accounts for 18 ± 7 per cent of the total flux density in the region at the peak frequency of 37 GHz. Comparison with 100 μm data indicates an average dust emissivity for the sub-regions of 0.5 ± 4.4 μK(MJy sr^(−1))^(−1). Finally, we translate the excess emission in the regions to an anomalous microwave emission (AME) emissivity relative to the optical depth at 250 μm. We find that this form of emissivity is independent of the AME significance and has a value somewhere in the order of 10^4 Jy.
Additional Information© 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2015 August 1. Received 2015 August 1; in original form 2015 June 18. This work was supported by the Strategic Alliance for the Implementation of New Technologies (SAINT – see www.astro.caltech.edu/chajnantor/saint/index.html) and we are most grateful to the SAINT partners for their strong support. We gratefully acknowledge support from the Kavli Operating Institute and thank B. Rawn and S. Rawn Jr. The CBI was supported by NSF grants 9802989, 0098734 and 0206416, and a Royal Society Small Research Grant. We are particularly indebted to the engineers who maintained and operated the CBI: Cristóbal Achermann, José Cortés, Cristóbal Jara, Nolberto Oyarace, Martin Shepherd and Carlos Verdugo. Constantinos Demetroullas is grateful to Anna Bonaldi for clarifying the equation for fitting spinning dust and to Matias Vidal for his valuable comments and support throughout many stages of this study. Constantinos also acknowledges the support of an STFC quota studentship and a President's Doctoral Scholarship from the University of Manchester and he is grateful to the European Research Council for support through the award of an ERC Starting Independent Researcher Grant (EC FP7 grant number 280127). Clive Dickinson is supported by an STFC Consolidated Grand (no. ST/L000768/1), an EU Marie Curie Re-Integration Grant and an ERC Starting Grant (No. 307209). Constantinos and Clive would like to thank NVSS, CORNISH, NED, SIMBAD and Green catalogue.
Published - MNRAS-2015-Demetroullas-2082-93.pdf
Submitted - 1507.08280v1.pdf