Planck intermediate results. XII: Diffuse Galactic components in the
  Gould Belt System
  We perform an analysis of the diffuse low-frequency Galactic components in
the Southern part of the Gould Belt system (130^\circ\leq l\leq 230^\circ and
-50^\circ\leq b\leq -10^\circ). Strong ultra-violet (UV) flux coming from the
Gould Belt super-association is responsible for bright diffuse foregrounds that
we observe from our position inside the system and that can help us improve our
knowledge of the Galactic emission. Free-free emission and anomalous microwave
emission (AME) are the dominant components at low frequencies (\nu < 40 GHz),
while synchrotron emission is very smooth and faint. We separate diffuse
free-free emission and AME from synchrotron emission and thermal dust emission
by using Planck data, complemented by ancillary data, using the "Correlated
Component Analysis" (CCA) component separation method and we compare with the
results of cross-correlation of foreground templates with the frequency maps.
We estimate the electron temperature T_e from H$\alpha$ and free-free emission
using two methods (temperature-temperature plot and cross-correlation) and we
obtain T_e ranging from 3100 to 5200 K, for an effective fraction of absorbing
dust along the line of sight of 30% (f_d=0.3). We estimate the frequency
spectrum of the diffuse AME and we recover a peak frequency (in flux density
units) of 25.5 \pm 1.5 GHz. We verify the reliability of this result with
realistic simulations that include the presence of biases in the spectral model
for the AME and in the free-free template. By combining physical models for
vibrational and rotational dust emission and adding the constraints from the
thermal dust spectrum from Planck and IRAS we are able to get a good
description of the frequency spectrum of the AME for plausible values of the
local density and radiation field.
