Arcetri Astrophysical Observatory

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Guidetta Torricelli

Broad Line Region structure

Recent studies on X-ray absorption variability on time scales of hours/days demonstrate that the X-ray "torus" is made of clouds with the same density and distance from the center as the BLR emission line clouds, thus suggesting a close link between the BLR and the X-ray circumnuclear absorber. Until now, this approach has been applied to a small number of cases. However, more long X-ray observations of bright sources with XMM-Newton and Suzaku, suitable for absorption variability analysis, are present in public archives and hence this X-ray absorption analysis can be applied to other sources. The idea is that the results of these observational studies will be fundamental for a better physical description of the absorbers and, therefore,for a better knowledge of the actual structure of the BLR. The analysis is in progress.

Research on AGN


The formation and evolution of Active Galactic Nuclei (AGN), attributed to accreting massive black holes (BHs), are closely related to the formation and evolution of the galaxies which host them. Our group has been studying the co-evolution of AGN, BHs, and their host galaxies for several years now. We rely on a multiwavelength approach, from the millimeter and the IR to the X-ray. Specifically, our group is engaged in studies of:

Research on the LOCAL UNIVERSE


Galaxy evolution is occurring at the present epoch in the Local Universe, through gas accretion and gas consumption via star formation, or through passive evolution. Evolutionary processes can be studied in nearby galaxies with a detail that high-redshift objects do not allow. We rely on a multiwavelength approach and comparison with theoretical predictions; special attention is given to the interstellar medium of star-forming and quiescent galaxies and how its properties vary with galaxy mass, metallicity, and environment. The ultimate aim is to exploit studies of nearby galaxies in the cosmological context to better understand how galaxies form and evolve. Specifically, our group is engaged in studies of:



How cosmic structures formed and how galaxies were assembled remain key open questions in the study of modern cosmology. Theoretical models of primordial star formation and observations of samples faint high-redshift galaxies and clusters are the cornerstone of our group. By combining results from observational and theoretical research, the ultimate aim is to constrain the epoch of structure and galaxy formation, and broaden our understanding of physical processes at work in the early universe. Specifically, our group is engaged in studies of:

Guido Risaliti

Main research interests:
1) Structure and geometry of the circumnuclear medium of AGN, particularly through hard X-ray observations of obscured sources.
2) Spectral energy distribution of AGN, X-ray to optical correlations, bolometric corrections and contribution of AGN to the cosmic backgrounds
3) Physics of Ultraluminous Infrared Galaxies (ULIRGs): analysis of the AGN and