IR-correlated 31 GHz radio emission from Orion East

Abstract

Lynds dark cloud LDN1622 represents one of the best examples of anomalous dust emission, possibly originating from small spinning dust grains. We present Cosmic Background Imager (CBI) 31 GHz data of LDN1621, a diffuse dark cloud to the north of LDN1622 in a region known as Orion East. A broken ring with diameter g\approx 20 arcmin of diffuse emission is detected at 31 GHz, at \approx 20-30 mJy beam${}^{-1}$ with an angular resolution of \approx 5 arcmin. The ring-like structure is highly correlated with Far Infra-Red emission at $12-100\mu$m with correlation coefficients of r \approx 0.7-0.8, significant at $\sim 10\sigma$. Multi-frequency data are used to place constraints on other components of emission that could be contributing to the 31 GHz flux. An analysis of the GB6 survey maps at 4.85 GHz yields a $3\sigma$ upper limit on free-free emission of 7.2 mJy beam${}^{-1}$ ($\la 30 per cent of the observed flux) at the CBI resolution. The bulk of the 31 GHz flux therefore appears to be mostly due to dust radiation. Aperture photometry, at an angular resolution of 13 arcmin and with an aperture of diameter 30 arcmin, allowed the use of IRAS maps and the {\it WMAP} 5-year W-band map at 93.5 GHz. A single modified blackbody model was fitted to the data to estimate the contribution from thermal dust, which amounts to $\sim$10percentat31GHz.Inthismodel,anexcessof1.52\pm 0.66Jy(2.3\sigma )isseenat31GHz.Futurehighfrequency$\sim$100-1000GHzdata,suchasthosefromthePlancksatellite,arerequiredtoaccuratelydeterminethethermaldustcontributionat31GHz.CorrelationswiththeIRAS$100 μ$mgaveacouplingcoefficientof$18.1\pm4.4 μ$K(MJy/sr)$^{-1}$, consistent with the values found for LDN1622.

8 pages, 3 figures, 3 tables, submitted to MNRAS

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• New constraints on the Polarization of Anomalous Microwave Emission in nearby molecular clouds
• Spitzer characterisation of dust in an anomalous emission region: the Perseus cloud
• Detection of Spectral Variations of Anomalous Microwave Emission with QUIJOTE and C-BASS
• New radio observations of anomalous microwave emission in the HII region RCW175
• On the Limitations of the Anomalous Microwave Emission Emissivity
• COMAP Early Science: VI. A First Look at the COMAP Galactic Plane Survey
• Using cm Observations to Constrain the Abundance of Very Small Dust Grains in Galactic Cold Cores
• AMI Observations of the Anomalous Microwave Emission in the Perseus Molecular Cloud
• The C-Band All-Sky Survey (C-BASS): Constraining diffuse Galactic radio emission in the North Celestial Pole region
• QUIJOTE scientific results -- X. Spatial variations of Anomalous Microwave Emission along the Galactic plane
• Observations of Free-Free and Anomalous Microwave Emission from LDN 1622 with the 100 m Green Bank Telescope
• Modelling the spinning dust emission from LDN 1780
• The Cosmic Background Imager 2
• Observations of Galactic star-forming regions with the Cosmic Background Imager at 31 GHz
• Large Radio Telescopes for Anomalous Microwave Emission Observations
• Constraints on free-free emission from Anomalous Microwave Emission Sources in the Perseus Molecular Cloud
• A characterization of the diffuse Galactic emissions in the anti-center of the Galaxy