Dust-correlated centimetre-wave radiation from the M 78 reflection nebula

An anomalous radio continuum component at cm-wavelengths has been observed in various sources, including dark clouds. This continuum component represents a new property of the ISM. In this work we focus on one particular dark cloud, the bright reflection nebula M 78. The main goal of this work is to investigate the cm-wave continuum emission in a prominent molecular cloud, nearby and with complementary observational data. We acquired Cosmic Background Imager (CBI) visibility data of M 78 at 31 GHz with an angular resolution of ∼ 5.8′, and CBI2 data at an angular resolution of ∼ 4.2′. A morphological analysis was undertaken to search for possible correlations with templates that trace different emission mechanisms. Using data from WMAP and the Rhodes/HartRAO 2326 MHz survey we constructed the spectral en-ergy distribution (SED) of M 78 in a 45 ′ circular aperture. We used results from the literature to constrain the physical conditions and the stellar content. The 5 GHz – 31 GHz spectral index in flux density (α = 1.89 ± 0.15) is significantly different from optically thin-free-free values. We also find closer morphological agreement with I