Coffee talks
Wednesday 17/12/2025 @ 10:30, Sala riunioni quarto piano e on line (meet.google.com/sue-bwvk-axf)
Elika Prameswari Fariyanto (Department of Astronomy The University of Tokyo/NAOJ), "Jet Collimation in the Low-Accreting System M84"
How the jet in active galactic nuclei (AGN) becomes collimated has been a long-standing issue in astrophysics. Although recent high-resolution VLBI analysis of an increasing number of AGN jet sources has significantly improved our understanding of jet collimation properties near supermassive black holes (SMBHs), previous jet collimation studies have been limited to bright and powerful jet sources. We investigate the collimation property of the nearby radio galaxy M84, which is a prototypical source of low-luminosity AGN (LLAGN), providing the opportunity to examine the jet collimation property at the lower end of the jet activity. Using multi-frequency VLBA observations from 1.4 to 88 GHz, complemented by archival VLA data, we trace the jet from a few hundred up to several million Schwarzschild radii. The reconstructed jet profile shows a clear geometric transition. The inner jet follows a semi-parabolic shape (W ? r^0.72), while the outer region becomes conical (W ? r^1.17), with the transition occurring around 10^4 Schwarzschild radii. This break radius is considerably smaller than what is seen in more powerful AGN jets, suggesting that low accretion rates reduce the external pressure support needed to maintain collimation over large distances. We also measure the frequency-dependent core shift using phase-referencing techniques and use these results to estimate the black hole location and the magnetic field strength near the jet base. M84 provides an important case for understanding how jet geometry responds to extremely weak accretion and serves as a key reference point within the LLAGN population.