Observations of Galactic star-forming regions with the Cosmic Background Imager at 31 GHz

Abstract

Studies of the diffuse Galactic radio emission are interesting both for better understanding the physical conditions in our Galaxy and for minimising 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 $\sim$4${}^{\prime }$.5 resolution and conduct an investigation of the spectral emission process in the regions at 4${}^{\prime }$.5 and 1${}^{\circ }$ resolution. We find that most of the emission in the regions is due to optically thin free-free. For 2 sub-regions of NGC 6334 and for a sub-region of W51 though, at 4${}^{\prime }$.5 resolution and at 31 GHz we detect less emission than expected from extrapolation of radio data at lower frequencies assuming a spectral index of $-$0.12 for optically thin free-free emission, at 3.3$\sigma$, 3.7$\sigma$ and 6.5$\sigma$ respectively. We also detect excess emission in a sub-region of NCG 6334 at 6.4$\sigma$, after ruling out any possible contribution from Ultra Compact HII (UCHII) regions. At 1${}^{\circ }$ resolution we detect a spinning dust component in the Spectral Energy Distribution (SED) of W40 that accounts for 18$\pm$7 % of the total flux density in the region at the peak frequency of 37 GHz. Comparison with 100 $\mu \mathrm{m}$ data indicate an average dust emissivity for the sub-regions of $0.5\pm 4.4$ $\mu$K(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 $\mu \mathrm{m}$. 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.

13 pages, 4 figures

References in corpus (10)

• Polarization Observations with the Cosmic Background Imager
• A refined model for spinning dust radiation
• Centimeter-wave continuum radiation from the rho Ophiuchi molecular cloud
• WMAP 3yr data with the CCA: anomalous emission and impact of component separation on the CMB power spectrum
• Hi Shells and Supershells in the I-GALFA Hi 21-cm Line Survey: I. Fast-Expanding Hi Shells Associated with Supernova Remnants
• CBI limits on 31 GHz excess emission in southern HII regions
• AMI limits on 15 GHz excess emission in northern HII regions
• Constraints on spinning dust towards Galactic targets with the VSA: a tentative detection of excess microwave emission towards 3C396
• A centimetre-wave excess over free-free emission in planetary nebulae
• Planck intermediate results. XXIII. Galactic plane emission components derived from Planck with ancillary data

Cited by in corpus (4)

• A revised catalogue of 294 Galactic supernova remnants
• The State-of-Play of Anomalous Microwave Emission (AME) Research
• Candidate radio supernova remnants observed by the GLEAM survey over $345^{\circ }<l<60^{\circ }$ and $180^{\circ }<l<240^{\circ }$
• QUIJOTE scientific results -- V. The microwave intensity and polarisation spectra of the Galactic regions W49, W51 and IC443