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23rd of November 2022
ATNF Colloquium
High-redshift Supermassive Black Holes grow in dusty, gas-rich environment
Quirino D’Amato (SISSA, Italy)
Abstract: A large fraction of supermassive black holes (SMBHs) located in Active Galactic Nuclei (AGN) at galaxy centres grow hidden by dust and gas. In the local Universe, the obscuration is often associated with the (sub-)pc-scale circumnuclear medium surrounding the SMBH (i.e. the so-called torus), as postulated by the Unified Schemes. However, deep X-ray observations have shown that the fraction of obscured AGN dramatically increases with redshift. In addition, thanks to the revolution introduced by new (sub-)mm observatories, in the last decade increasingly detections of the dusty, gas-rich interstellar medium (ISM) have been collected in the host galaxies of distant (z≳1.5) AGN. The physical properties of the ISM in galaxies change rapidly with redshift and, on average, distant AGN host galaxies are found more compact and denser than their local counterpart. These results suggest that the increased obscuration with redshift might occur on the host galaxy kpc-scale. Observational evidence shows that distant large-scale structures are often composed of gas-rich members, including the progenitor of the future brightest cluster galaxies. Moreover, diffuse large reservoirs of cold gas have been detected in the central regions of the intra-cluster medium (ICM) in many proto-clusters. Galaxy clusters are the largest virialized structures in the Universe, and most of their assembly takes place at the cosmic epoch where both star formation and black hole accretion peak (1< z <3). Exploring the interplay between nuclear activity, star formation and gas supply in such objects addresses the processes responsible for the build-up of present-day most massive galaxies. The presence of such an extremely dense environment strongly affects the galaxy-SMBH co-evolution through mechanical/radiative feedback processes; in addition, AGN are known to produce powerful relativistic-particle jets onto scales of several hundreds of kpc, and increasingly evidence have shown that AGN-feedback can extend on distances far beyond the host galaxy scale.

In this talk I will review the main recent observational results about the ISM content in distant AGN and proto-cluster, highlight the importance of a multi-wavelength approach and high-resolution observations in determining the ISM/ICM gas reservoir properties such as size, morphology, distribution and kinematics. I will discuss the implications of such findings in modelling the evolution of massive galaxies and large-scale structures across cosmic time, and the role of AGN feedback in regulating such an evolution. In addition, I will discuss the role of the ISM in obscuring high-z AGN and the incidence of the obscured AGN fraction as a function of the redshift, presenting multi-wavelength observations and numerical simulations.

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