Main Colloquium
Prof. John McKean	SCHEDULED

Kapteyn Astronomical Institute, University of Groningen & ASTRON, Dwingeloo, The Netherlands

Gravitational lensing provides a powerful probe of the global mass properties of galaxies, which are best tested using observations at extremely high angular resolution. In addition, through detailed observations of the lensed images, it is possible to place tight constraints on the nature of dark matter through measuring the abundance and properties of low mass haloes via their subtle gravitational lensing signal. Here, we first present new observations with the VLA and HSA to better understand the source of so-called flux-ratio anomalies in four image gravitational lenses, which historically provided the first constraints on CDM using lensing studies. Next, we will present the analysis of the mass properties of ten massive elliptical galaxies at intermediate redshifts, by combining gravitational lensing and the sensitivity and resolving power of the Atacama Large Millimetre Array (ALMA) and global Very Long Baseline Interferometry (radio VLBI). Using imaging at 25 to a few milli-arcsecond resolution, we find that complex mass models with angular structure are strongly favoured by the data. In addition, such observations are sensitive to small-scale structure either in the lens or along the line-of-sight to the background source. From such an analysis of the data from global VLBI observations, we detect of a low mass (million solar mass) dark object, whose properties are inconsistent with a dark matter halo from either cold or warm dark matter models, but may be in agreement with more exotic models, like self-interacting dark matter. Finally, we present a brief overview of future studies using the SKA and a likely African VLBI facility that includes the SKAMPI, MPG-DZA and AMT dishes. Throughout we will also provide some asides on the pc-scale structure of radio jets, constraints on galactic-scale magnetic fields and electron densities, and the super-resolved (about 10 to 20 pc-scale) properties of starburst galaxies at redshifts 1 to 4.

	Special Colloquium
Niloofar Pourjafari	SCHEDULED

University of Calgary

Magnetic fields are an important component of the interstellar medium, influencing the transport of cosmic rays and the interaction between galactic disks and halos. NGC 891, one of the closest Milky Way analogues, provides an excellent opportunity to study these processes in an edge-on system. In this talk, I will present new VLA S-band polarization observations of NGC 891 combined with existing C-band data from the CHANG-ES survey. We detect a large-scale polarized halo and find evidence for an ordered magnetic field extending across the galaxy. The observations suggest that much of the observed polarized emission originates on the near side of the galaxy, providing a new perspective on the magnetized halo of this highly inclined system. We also identify localized polarized structures on kiloparsec scales in the north-eastern halo that coincide with diffuse X-ray and Hα emission. These features likely trace magnetic fields associated with recent star formation activity and feedback, possibly including a superbubble powered by clustered supernovae. Together, these observations reveal both the global magnetic field structure of NGC 891 and the influence of local star formation activity on its halo.