Observations of Galactic star-forming regions with the Cosmic Background
  Imager at 31 GHz
  Studies of the diffuse Galactic radio emission are interesting both for
better understanding the physical conditions in our Galaxy and for minimising
the contamination in cosmological measurements. Motivated by this we present
Cosmic Background Imager 31 GHz observations of the Galactic regions NGC 6357,
NGC 6334, W51 and W40 at $\sim$4$'$.5 resolution and conduct an investigation
of the spectral emission process in the regions at 4$'$.5 and 1$^{\circ}$
resolution. We find that most of the emission in the regions is due to
optically thin free-free. For 2 sub-regions of NGC 6334 and for a sub-region of
W51 though, at 4$'$.5 resolution and at 31 GHz we detect less emission than
expected from extrapolation of radio data at lower frequencies assuming a
spectral index of $-$0.12 for optically thin free-free emission, at
3.3$\sigma$, 3.7$\sigma$ and 6.5$\sigma$ respectively. We also detect excess
emission in a sub-region of NCG 6334 at 6.4$\sigma$, after ruling out any
possible contribution from Ultra Compact HII (UCHII) regions. At 1$^{\circ}$
resolution we detect a spinning dust component in the Spectral Energy
Distribution (SED) of W40 that accounts for 18$\pm$7 % of the total flux
density in the region at the peak frequency of 37 GHz. Comparison with 100
${\rm \mu m}$ data indicate an average dust emissivity for the sub-regions of
$0.5\pm4.4$ $\mu$K(MJy sr$^{-1}$)$^{-1}$. Finally we translate the excess
emission in the regions to an Anomalous Microwave Emission (AME) emissivity
relative to the optical depth at 250 ${\rm \mu m }$. We find that this form of
emissivity is independent of the AME significance and has a value somewhere in
the order of 10$^4$ Jy.
