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Published October 1, 2010 | Published
Journal Article Open

Infrared-correlated 31-GHz radio emission from Orion East


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-like structure with diameter ≈20 arcmin of diffuse emission is detected at 31 GHz, at ≈20–30 mJy beam^(−1) with an angular resolution of ≈5 arcmin. The ring-like structure is highly correlated with far-infrared (FIR) emission at 12–100 μm with correlation coefficients of r ≈ 0.7–0.8, significant at ~10σ. The FIR-correlated emission at 31 GHz therefore appears to be mostly due to radiation associated with dust. Multifrequency 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 3σ upper limit on free–free emission of 7.2 mJy beam^(−1) (≾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 Wilkinson Microwave Anisotropy Probe 5-yr 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 ~10 per cent at 31 GHz. In this model, an excess of 1.52 ± 0.66 Jy (2.3σ) is seen at 31 GHz. Correlations with the IRAS 100 μm gave a coupling coefficient of 18.1 ± 4.4 μK (MJy sr^(−1))^(−1), consistent with the values found for LDN1622.

Additional Information

© 2010 The Authors. Journal compilation © 2010 RAS. Accepted 2010 May 25. Received 2010 May 21; in original form 2010 March 15. Article first published online: 29 Jun. 2010. We thank the anonymous referee for providing suggestions that have improved the clarity of the paper. This work was supported by the Strategic Alliance for the Implementation of New Technologies (SAINT – see http://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: Cristόbal Achermann, José Cortés, Cristόbal Jara, Nolberto Oyarace, Martin Shepherd and Carlos Verdugo. CD acknowledges an STFC Advanced Fellowship and ERC grant under the FP7.We acknowledge the use of the Legacy Archive for Microwave Background Data Analysis (LAMBDA). Support for LAMBDA is provided by the NASA Office of Space Science. We used data from the Southern H-Alpha Sky Survey Atlas (SHASSA), which is supported by the National Science Foundation.

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