Astronomy Colloquium

The interstellar medium (ISM) is a turbulent, multi-phase, magnetic environment. It is home to vastly different gas phases, from cold, dense clouds to hot, tenuous plasma. Magnetic fields thread this interstellar environment, helping to sculpt galaxies through their influence on a diverse range of physics, from cosmic ray propagation to star formation. The magnetic ISM is also a formidable foreground for experimental cosmology, especially for studies of the polarized cosmic microwave background. I will discuss new ways to probe interstellar magnetism, the phase structure of interstellar gas, and the link between the two, with a particular focus on morphology: how the spatial structure of gas and dust encodes information about the physics of the ISM.

I will first review the progress in surveys of the most distant quasars, including the latest record-breaking quasars discovered by Euclid at z>7.5. They are powered by billion solar mass black holes, possible only by a combination of massive early black hole seeds with highly efficient and sustained accretion. I will present results of surveys of early quasars and their environments using JWST. While rapid early black hole growth is accompanied by intense star formation and feedback in their host galaxies, the diverse quasar environment unveiled by these observations suggests a complex interplay between black hole accretion, galaxy assembly, the physics of reionization and the emergence of early large scale structure. JWST observations have revealed a new population of active galactic nuclei (AGN), the "Little Red Dots" (LRDs), with high abundance and multiwavelength properties different from those of typical AGN and quasars. I will discuss the observations of LRDs and constraints on their physical nature in relation to early black hole growth. A subset of LRDs, both those discovered at high-redshift with JWST, and detected in the local universe, strongly suggest the presence of optically-thick gas envelops surrounding the central energy source, consistent with scenarios of super-Eddington accretion, and could be the missing link between black hole seeds and luminous early quasars.

TBD

Fast radio bursts (FRBs) are millisecond-duration flashes of coherent radio emission originating from extragalactic distances, offering a unique view into the physics of compact objects and their surrounding environments. Despite their brief and unpredictable nature, precise localizations of a small number of FRBs have already revealed a striking diversity in host galaxies, local environments, and burst properties - suggesting multiple progenitor channels linked to extreme compact objects. However, the nature of FRB sources remains one of the most exciting mysteries in astrophysics.

In this talk, I will show how combining high-precision localizations with detailed studies of FRB radio properties can disentangle their origins and probe the extreme plasma environments in which they reside. I will present new results from the now science-operational CHIME/FRB Outriggers project, which is transforming the world's most prolific FRB discovery instrument into a very long baseline interferometric array. The Outriggers have already approximately doubled the number of FRB host galaxies, with many more expected in the near future. Beyond localizations, the radio properties themselves encode key physical insights: scintillation measurements constrain the emission region to magnetospheric scales, directly informing the emission mechanism, while a declining electron column density over time observed in a repeating FRB points to an origin within an expanding supernova remnant. We are now entering a regime where large samples of FRBs have both detailed radio diagnostics and secure host-galaxy identifications, enabling a far more complete understanding of the extreme astrophysical systems that power FRBs.