An excess of emission in the dark cloud LDN 1111 with the Arcminute Microkelvin Imager

TL;DR

This study reports a significant microwave emission excess in the dark cloud LDN 1111, consistent with spinning dust models, based on observations with the Arcminute Microkelvin Imager.

Contribution

First detection of microwave emission excess in LDN 1111 consistent with spinning dust, using AMI observations and spectral modeling.

Findings

Emission exceeds thermal free-free predictions by >15 sigma

Spectral fit aligns with spinning dust model parameters

Results support spinning dust as the emission mechanism

Abstract

We present observations of the Lynds' dark nebula LDN 1111 made at microwave frequencies between 14.6 and 17.2 GHz with the Arcminute Microkelvin Imager (AMI). We find emission in this frequency band in excess of a thermal free--free spectrum extrapolated from data at 1.4 GHz with matched uv-coverage. This excess is > 15 sigma above the predicted emission. We fit the measured spectrum using the spinning dust model of Drain & Lazarian (1998a) and find the best fitting model parameters agree well with those derived from Scuba data for this object by Visser et al. (2001).