Special Colloquium
Dr. Yaherlin Diaz	SCHEDULED

Universidad Diego Portales, Chile

We present a study of mid-infrared emission in a sample of 138 local active galactic nuclei (AGN; ⟨z⟩ = 0.03 - covering the central ~2.16 kpc), using low-resolution Spitzer/IRS observations. We measured the fluxes of the 6.2, 7.7, 8.6, and 11.3 µm polycyclic aromatic hydrocarbon (PAH) features to assess their viability as tracers of star formation in AGN hosts. PAH features were detected in over 68% (106/138) of the sample, with the more resilient 11.3 µm feature present in 92% of sources. We find that the PAH-based star formation rate (SFR) correlates positively with X-ray luminosity, suggesting a potential connection between the AGN activity and star formation on kiloparsec scales. However, we find no significant correlation between PAH emission and AGN properties such as Eddington ratio or black hole mass. Interestingly, in unobscured or type 1 AGN (column densities log(NH) < 22), the 11.3 µm PAH feature is more correlated with AGN emission, implying that PAH molecules can be excited by the central engine only when not shielded by intervening material. Our results highlight the need for specific corrections when using PAH features as star formation indicators in AGN environments.

	Main Colloquium
Prof. Dominik Schleicher	SCHEDULED

Dipartimento di Fisica - Sapienza, Università di Roma

Theoretical models and observational data provide strong support for the origin of supermassive black holes via collision-based formation channels. An analysis of Nuclear Star Clusters in the Local Universe suggests that these are stable when the typical collision timescales are much longer compared ot the ages of these systems. We present here a suite of numerical simulations designed to test this scenario, where we widely vary the typical collision timescales as compared to the ages of the system. Our results show that the efficiency to form central massive objects strongly depends on the ratio of cluster ages over collision timescales, which can be expressed in relation to a typical mass scale for collisions. We present some of the largest recently pursued N-body simulations designed to verify this scenario, showing the efficient formation of a supermassive black hole with more than 20.000 solar masses through stellar collisions. We compare our results with the Young Massive Star Clusters detected in high-redshift galaxies via the James Webb Space Telescope, providing an expected relation between the masses of these clusters and the massive black holes forming within them. We further show and discuss how the presence of gas may alter the predictions from the N-body simulations.