Active Galactic Nuclei XVI: A Sea of Discoveries

Black Hole Growth in the Densest Regions of the Universe: AGN activity in protoclusters from Cosmic dawn to the present days

16 Jun 2026, 17:25

15m

Sala Conferenze presso Autorità di Sistema Portuale (Brindisi)

Talk S4 - Binary and Dual AGN Systems: Studying the observational signatures, dynamics, and gravitational wave implications of closely separated and merging black hole systems

Speaker

Alberto Traina (Istituto Nazionale di Astrofisica (INAF))

Description

Recent observations suggest that active galactic nucleus (AGN) activity is enhanced in overdense environments, such as galaxy protoclusters, compared to the field. However, these results are based on limited observational samples and heterogeneous selections of AGN and host galaxies, making it difficult to identify the physical origin of this apparent enhancement and to disentangle genuine environmental effects from selection-driven biases.
Cosmological simulations provide a powerful avenue to overcome these limitations, as their large volumes enable the systematic study of hundreds of galaxy clusters and their progenitors across cosmic time. In this talk, I will present the first statistical analysis of the demography and evolution of supermassive black holes (SMBHs) in galaxy protoclusters from the cosmic dawn to the present day, based on the IllustrisTNG simulation suite.
I will show that, at fixed host-galaxy stellar mass, the AGN fraction in protoclusters is comparable to that in the field, indicating that overdense environments do not significantly enhance black hole accretion through direct environmental triggering. Nevertheless, an apparent enhancement of the AGN fraction as a function of redshift emerges when integrating over the evolving galaxy population. We demonstrate that this effect is driven primarily by differences in the stellar-mass distributions of galaxies in overdense regions, which host massive galaxies and actively accreting SMBHs earlier than the field. This interpretation is further supported by the analysis of the AGN bolometric luminosity function and the cosmic black hole accretion rate density, which reveal a dominant contribution from protoclusters at high redshift. Finally, I will discuss the comparison between simulation predictions and current observational constraints, and the implications for interpreting AGN activity in dense environments.