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 ($130^\circ≤ l≤ 230^\circ$ and $-50^\circ≤ b≤ -10^\circ$). Strong 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 ($ν < 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$α$ and free-free emission using two methods (temperature-temperature plot and cross-correlation) and we consistently obtain $T_ e$ ranging from 7000 to 2000 K for a dust absorption fraction of $f_ d=0$--0.5. We estimate the frequency spectrum of the diffuse AME and we recover a peak frequency (in flux density units) of $25.5± 1.5$ 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.