Events, Seminars, Talks

Abstract
The galaxy population in today's Universe exhibits remarkable diversity\; from blue, star-forming disk galaxies like the Milky Way – hosting bulges, bars and black holes with varying accretion rates in their centres – to red elliptical galaxies that have ceased forming stars. Understanding when and how this diverse population first emerged are questions at the forefront of extragalactic astronomy. Owing to the finite speed of light, we can see galaxies farther back in time by observing galaxies over great distances using state-of-the-art instrumentation on board space telescopes. These distant galaxy populations provide snapshots of the early evolution of today's galaxy population. Our understanding of galaxy formation and evolution predominantly comes from large imaging and limited slit spectroscopy surveys from which we infer physical properties of galaxies described by single quantities. These fail to capture the complexity of the star formation distribution, chemical composition and movement of stars and gas within galaxies. In the next 5 years, a huge leap in our understanding of how the earliest galaxies formed and evolved into today's galaxy population can be made using slitless spectroscopy with the James Webb Space Telescope, Euclid and the Roman Space Telescope. In one snapshot, slitless spectroscopy captures high resolution maps of multiple critical physical processes in hundreds of distant galaxies, expanding sample sizes of spectroscopic surveys by orders of magnitude, while providing the first resolved view of galaxy evolution across cosmic time. In this talk I will describe what HST and JWST slitless spectroscopy has already revealed about the size growth, dust distribution, ongoing star formation and its quenching in galaxies across cosmic time. Followed by the first high resolution view of Supermassive Black Hole (SMBH) activity in galaxies at cosmic noon. Finally, I will look to the future, describing how slitless spectroscopy taken with Euclid, Roman, HST and JWST will transform our understanding of how the earliest galaxies evolved into today's diverse population.

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Gaia, developed and operated by the European Space Agency, was launched in 2013, and operated until January 2025. It's creating a revolutionary six-dimensional map of our Galaxy by measuring the accurate distances and space motions of some three billion stars. While the measurement of star positions has a very long history, stretching back more than 2000 years, Gaia's accuracies exploit the numerous advantages of measurements made from above the Earth's atmosphere. Absolute positional accuracies of order 10 micro-arcsec can register stellar motions that would require more than 10,000 years to be discerned on the ground.  This is providing a major advance in understanding stellar evolution, and in unravelling the composition, structure, and history of our Galaxy's formation. I will not focus on the technical details, but provide a "big picture" of Gaia's scientific advances.

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Active galactic nuclei are mostly powered by inflow through accretion disks onto central supermassive black holes. Beyond a few times their Schwarzschild radius, gravitational instability in these disks leads to self-regulated formation and evolution of massive stars which chemically enrich their neighborhood along with stellar-mass black holes. These compact remnants are captured by coexisting massive main sequence stars, form close binaries, readily merge, and excite intense gravitational waves with potentially observable electromagnetic signatures. The massive stars' migration, with or without black hole cores, efficiently transporting mass regardless of the Eddington limit and promoting the rapid growth of supermassive black holes in the early Universe. Analogous physical processes are also relevant in the context of planet formation in protostellar disks. They account for the persistent super-solar metallicity, especially in Nitrogen and iron, inferred from broad emission lines of high and low redshift AGNs. To arrange a visit with the speaker during the visit, please contact their host: Haochang Jiang

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