The innermost regions of the Seyfert 2 galaxies NGC613 and NGC1808: the X-ray and millimeter view

One of the main goals of this Thesis is to verify whether the gas traced by the CO transitions in millimeter band can be considered responsible for the obscuration measured in X-ray observations. This multi-band analysis could give information on the characteristic scales where AGN obscuration occurs. In particular, we carried out the multi-frequency study of the local galaxies NGC613 (z = 0.0049) and NGC1808 (z = 0.0033), which belong to the Seyfert 2 galaxies class. The X-ray spectral analysis of the sources were carried on in the energy bands 0.3-7.0 keV (Chandra) and 0.3-10 keV (XMM-Newton). The combination of the data from these two satellites allows us to study not only the main features of the obscuring molecular torus, but also the underlying AGN continuum emission and estimate its intrinsic luminosity. The intrinsic absorption along the line of sight of the source is measured through the column density, which was found to be of the order of 10^{23} for both sources, indicating that NGC613 and NGC1808 host a heavily obscured AGN. The galaxies under examination were observed in the millimetric band, by using the ALMA. We obtained a range of possible values for N(H), to be compared with the those obtained from X-ray spectral analyses. We obtain agreement between ALMA data and X-ray ones by using physically motivated models, which assume a clumpy distribution of the obscuring material. We then conclude that the most plausible geometry of the molecular torus is patchy, instead of uniform and doughnut-like, for both sources.