Magnetic Growth in Transient (Galactic) Dynamos

Main Colloquium
Dr. Neco Kriel
SCHEDULED
Australian National University

Small-scale dynamos are thought to explain how weak magnetic fields in the early universe were amplified to the strengths we observe in galaxies today. While this process is usually associated with the early stages of galaxy formation, mergers between mature galaxies can trigger bursts of turbulence that reignite dynamo activity. A key question is how quickly the magnetic energy grows during these events. Seminal theories suggest this process could be too slow to matter – taking longer than the age of the universe – because growth is limited by slow diffusion. However, recent works have begun to challenge this idea. In this talk, I will present new simulations that explore this question and offer insight into the processes that regulate magnetic growth in galaxies.

Re-evaluating 11.3 microns Polycyclic Aromatic Hydrocarbon as Star Formation Tracer in Active Galactic Nuclei

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.

Origin of supermassive black holes - an astrophysical assessment of possible formation channels"

Main Colloquium
Prof. Dominik Schleicher
SCHEDULED
Dipartimento di Fisica - Sapienza, Università di Roma

TBD