CBI limits on 31 GHz excess emission in southern HII regions

Abstract

We have mapped four regions of the southern Galactic plane at 31 GHz with the Cosmic Background Imager. From the maps, we have extracted the flux densities for six of the brightest \hii regions in the southern sky and compared them with multi-frequency data from the literature. The fitted spectral index for each source was found to be close to the theoretical value expected for optically thin free-free emission, thus confirming that the majority of flux at 31 GHz is due to free-free emission from ionised gas with an electron temperature of $\approx 7000-8000$ K. We also found that, for all six sources, the 31 GHz flux density was slightly higher than the predicted value from data in the literature. This excess emission could be due to spinning dust or another emission mechanism. Comparisons with $100\mu$m data indicate an average dust emissivity of $3.3\pm 1.7\mu$K (MJy/sr)${}^{-1}$, or a 95 per cent confidence limit of $<6.1\mu$K (MJy/sr)${}^{-1}$. This is lower than that found in diffuse clouds at high Galactic latitudes by a factor of $\sim 3-4$. The most significant detection ($3.3\sigma$) was found in $G284.3-0.3$ (RCW49) and may account for up to $\approx 30$ per cent of the total flux density observed at 31 GHz. Here, the dust emissivity of the excess emission is $13.6\pm 4.2\mu$K (MJy/sr)${}^{-1}$ and is within the range observed at high Galactic latitudes. Low level polarised emission was observed in all six sources with polarisation fractions in the range $0.3-0.6$ per cent. This is likely to be mainly due to instrumental leakage and is therefore upper an upper limit to the free-free polarisation. It corresponds to an upper limit of $\sim 1$ per cent for the polarisation of anomalous emission.

arXiv commentAccepted in MNRAS. 12 pages, 10 figures, 5 tables

References in corpus (37)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Preliminary Maps and Basic Results
• First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Foreground Emission
• Extrapolation of Galactic Dust Emission at 100 Microns to CMBR Frequencies Using FIRAS
• IRIS: A new generation of IRAS maps
• Electric Dipole Radiation from Spinning Dust Grains
• Diffuse Galactic Emission from Spinning Dust Grains
• The Anisotropy of the Microwave Background to l = 3500: Deep Field Observations with the Cosmic Background Imager
• Microwave ISM Emission Observed by WMAP
• Extended Mosaic Observations with the Cosmic Background Imager
• The Anisotropy of the Microwave Background to l = 3500: Mosaic Observations with the Cosmic Background Imager
• An Anomalous Component of Galactic Emission
• Microwave Emission at High Galactic Latitudes
• Towards a free-free template for CMB foregrounds
• Polarization Observations with the Cosmic Background Imager
• Magnetic Dipole Microwave Emission from Dust Grains
• A determination of the Spectra of Galactic components observed by WMAP
• Detection of anomalous microwave emission in the Perseus molecular cloud with the COSMOSOMAS experiment
• Implications of the Cosmic Background Imager Polarization Data
• Morphological analysis of the cm-wave continuum in the dark cloud LDN1622
• Tentative Detection of Electric Dipole Emission from Rapidly Rotating Dust Grains
• Microwave ISM Emission in the Green Bank Galactic Plane Survey: Evidence for Spinning Dust
• Early-type stars in the core of the young open cluster Westerlund2
• First results from the Very Small Array -- I. Observational methods
• The Quest for Microwave Foreground X
• A New Spin on Galactic Dust
• The large-scale anomalous microwave emission revisited by WMAP
• Reappraising foreground contamination in the COBE-DMR data
• NGC 3576 and NGC 3603: Two Luminous Southern HII Regions Observed at High Resolution with the Australia Telescope Compact Array
• Polarization Observations of the Anomalous Microwave Emission in the Perseus Molecular Complex with the Cosmosomas Experiment
• An upper limit on anomalous dust emission at 31 GHz in the diffuse cloud [LPH96]201.663+1.643
• Constraints on spinning dust towards Galactic targets with the VSA: a tentative detection of excess microwave emission towards 3C396
• Anomalous radio emission from dust in the Helix
• Microwave Emission from Aligned Dust
• Multiwavelength studies of WR 21a and its surroundings
• Observations of the Cosmic Microwave Background and Galactic Foregrounds at 12-17 GHz with the COSMOSOMAS Experiment
• Limits on the Polarization of the Cosmic Microwave Background Radiation at Multipoles up to l~2000

Cited by in corpus (34)

• A refined model for spinning dust radiation
• Planck early results. XXI. Properties of the interstellar medium in the Galactic plane
• The State-of-Play of Anomalous Microwave Emission (AME) Research
• Spinning dust emission: the effect of rotation around a non-principal axis
• Anomalous Microwave Emission from the HII region RCW175
• Radio source calibration for the VSA and other CMB instruments at around 30 GHz
• VSA Observations of the Anomalous Microwave Emission in the Perseus Region
• A multi-wavelength investigation of RCW175: an HII region harboring spinning dust emission
• Constraints on the Polarization of the Anomalous Microwave Emission in the Perseus Molecular Complex from 7-year WMAP data
• Spitzer characterisation of dust in an anomalous emission region: the Perseus cloud
• Bayesian component separation and CMB estimation for the 5-year WMAP temperature data
• AMI limits on 15 GHz excess emission in northern HII regions
• AMI observations of Lynds Dark Nebulae: further evidence for anomalous cm-wave emission
• A Measurement of Arcminute Anisotropy in the Cosmic Microwave Background with the Sunyaev-Zel'dovich Array
• Dust-correlated centimetre-wave radiation from the M 78 reflection nebula
• Planck intermediate results. XII: Diffuse Galactic components in the Gould Belt System
• IR-correlated 31 GHz radio emission from Orion East
• An excess of emission in the dark cloud LDN 1111 with the Arcminute Microkelvin Imager
• The QUaD Galactic Plane Survey II: A Compact Source Catalog
• New radio observations of anomalous microwave emission in the HII region RCW175
• Derivation of an Analytical Approximation of the Spectrum of Spinning Dust Emission
• On the Limitations of the Anomalous Microwave Emission Emissivity
• Using cm Observations to Constrain the Abundance of Very Small Dust Grains in Galactic Cold Cores
• COMAP Early Science: VI. A First Look at the COMAP Galactic Plane Survey
• AMI Observations of the Anomalous Microwave Emission in the Perseus Molecular Cloud
• Detailed study of the microwave emission of the supernova remnant 3C 396
• A 33 GHz VSA survey of the Galactic plane from 27 to 46 degrees
• Resolved observations at 31 GHz of spinning dust emissivity variations in $\rho$ Oph
• Anomalous Microwave Emission in HII regions: is it really anomalous? The case of RCW 49
• Modelling the spinning dust emission from LDN 1780
• The Cosmic Background Imager 2
• Large Radio Telescopes for Anomalous Microwave Emission Observations
• Observations of Galactic star-forming regions with the Cosmic Background Imager at 31 GHz
• Observations of Anomalous Microwave Emission from HII regions