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 degrees <= l <= 230 degrees and -50 degrees <= b <= -10 degrees). Strong ultra-violet 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 separated 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 compared our results with the results of cross-correlation of foreground templates with the frequency maps. We estimated the electron temperature T-e from Ha and free-free emission using two methods (temperature-temperature plot and cross-correlation) and obtained 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 estimated the frequency spectrum of the diffuse AME and recovered a peak frequency (in flux density units) of 25.5 +/- 1.5 GHz. We verified the reliability of this result with realistic simulations that include 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 present a good description of the AME frequency spectrum for plausible values of the local density and radiation field.