Spectrum of the Anomalous Microwave Emission in the North Celestial Pole
  with WMAP 7-Year data
  We estimate the frequency spectrum of the diffuse anomalous microwave
emission (AME) on the North Celestial Pole (NCP) region of the sky with the
Correlated Component Analysis (CCA) component separation method applied to WMAP
7-yr data. The NCP is a suitable region for this analysis because the AME is
weakly contaminated by synchrotron and free-free emission. By modeling the AME
component as a peaked spectrum we estimate the peak frequency to be
$21.7\pm0.8$\,GHz, in agreement with previous analyses which favored $\nu_{\rm
p}<23$\,GHz. The ability of our method to correctly recover the position of the
peak is verified through simulations. We compare the estimated AME spectrum
with theoretical spinning dust models to constrain the hydrogen density $n_{\rm
H}$. The best results are obtained with densities around 0.2--0.3\,cm$^{-3}$,
typical of warm ionised medium (WIM) to warm neutral medium (WNM) conditions.
The degeneracy with the gas temperature prevents an accurate determination of
$n_{\rm H}$, especially for low hydrogen ionization fractions, where densities
of a few cm$^{-3}$ are also allowed.
