Coffee talks
Monday 16/01/2023 @ 14:30, Sala riunioni quarto piano e on-line (meet.google.com/sue-bwvk-axf)
Andrealuna Pizzetti (Clemson University, SC, USA), "To the torus and beyond: an X-ray study of AGN tori morphology"
Active galactic nuclei (AGN) are powered by accreting supermassive black holes, surrounded by a torus of obscuring material. Recent studies have shown how the torus structure, formerly thought to be homogeneous, appears to be ‘patchy’: the detection of variability in the line-of-sight (los) hydrogen column density (NH_los), in fact, matches the description of an obscurer with a more complex structure made of clouds with different density. In this work we perform a multi-epoch analysis of the Seyfert 2 galaxy NGC 7479's X-ray spectra, covering a time span of ~20 years. This allowed us to put tight constraints on its torus global properties such the covering factor, the inclination angle and the average column density. The NH_los variability we measured between different epochs strongly favors a clumpy torus scenario. The best fit parameters suggests a disentanglement of the reflection and the absorption material inside the torus; in particular the presence of a thick (>10^25 cm^-2) "inner ring" is required to explain the reflection dominated spectra. The ongoing ALMA campaign focused on the direct imaging of this inner structure and the same study on an extended sample of galaxies will also be discussed.