Dust-correlated cm wavelength continuum emission from translucent clouds ζ Oph and LDN 1780
The diffuse cm wave IR-correlated signal, the 'anomalous' CMB foreground, is thought to arise in the dust in cirrus clouds. We present Cosmic Background Imager (CBI) cm wave data of two translucent clouds, ζ Oph and LDN 1780 with the aim of characterizing the anomalous emission in the translucent cloud environment. In ζ Oph, the measured brightness at 31 GHz is 2.4σ higher than an extrapolation from 5-GHz measurements assuming a free–free spectrum on 8 arcmin scales. The SED of this cloud on angular scales of 1° is dominated by free–free emission in the cm range. In LDN 1780 we detected a 3σ excess in the SED on angular scales of 1° that can be fitted using a spinning dust model. In this cloud, there is a spatial correlation between the CBI data and IR images, which trace dust. The correlation is better with near-IR templates (IRAS 12 and 25 μm) than with IRAS 100 μm, which suggests a very small grain origin for the emission at 31 GHz. We calculated the 31-GHz emissivities in both clouds. They are similar and have intermediate values between that of cirrus clouds and dark clouds. Nevertheless, we found an indication of an inverse relationship between emissivity and column density, which further supports the VSGs origin for the cm emission since the proportion of big relative to small grains is smaller in diffuse clouds.
Additional Information© 2011 The Authors. Monthly Notices of the Royal Astronomical Society © 2011 RAS. Accepted 2011 February 17. Received 2011 February 17; in original form 2010 August 11. Article first published online: 11 APR 2011. We are most grateful to Mika Juvela who kindly shared with us the LDN 1780 ISO images. We thank an anonymous referee for a thorough reading and very useful comments. MV acknowledges the funding from Becas Chile. SC acknowledges support from a Marie Curie International Incoming Fellowship (REA-236176), from FONDECYT grant 1100221, and from the Chilean Center for Astrophysics FONDAP 15010003. CD acknowledges an STFC Advanced Fellowship and ERC grant under FP7. LB and RB acknowledge support from CONICYT project Basal PFB-06. This work has been carried out within the framework of a NASA/ADP ROSES-2009 grant, n. 09-ADP09-0059. 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. 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. 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.
Published - Vidal2011p15477Mon_Not_R_Astron_Soc.pdf