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New insights into early galaxy formation with JWST and ALMA
Joris WitstokNiels Bohr InstituteDate: Friday 3 October 2025Time: 3 pm Venue: AT 101
Cosmic reionization began when ultraviolet (UV) radiation produced in the first galaxies began illuminating the cold, neutral gas that filled the primordial Universe. Recent JWST observations have shown that surprisingly UV-bright galaxies were in place beyond redshift z = 14, when the Universe was less than 300 Myr old, sparking a debate on the nature of these early systems. I will present spectroscopy from the JWST Advanced Deep Extragalactic Survey (JADES) of a galaxy at redshift z = 13.0 that reveals a singular, bright emission line unambiguously identified as Lyman-α (Lyα), the principal hydrogen transition. Together with an extremely blue UV continuum, the unexpected Lyα emission indicates that the galaxy is a prolific producer and leaker of ionising photons, suggesting that massive, hot stars or an active galactic nucleus have commenced reionisation early on. I will further present new observations from the Atacama Large Millimeter/submillimeter Array (ALMA), which have begun to provide vital insights on the gas, metal and dust content of z > 10 galaxies. Comparing the accurate ALMA redshifts to those measured purely from the Lyα break, even spectroscopically, we find damped Lyα (DLA) absorption can cause systematic overestimates of up to Δz ~ 0.5, suggesting the presence of large neutral gas reservoirs. While the [C II] 158 μm line remains undetected at z > 10, several detections of bright [O III] 88 μm emission agree well with local SFR scaling relations, indicating early galaxies rapidly enrich in oxygen (>10% solar) within a few hundred million years after the Big Bang.
Cafe AP
Date: Friday 10 October 2025Time: 3 pm Venue: AT 101
A Local View of Stellar Astrophysics in the Early Universe
Grace TelfordPrincetonDate: Friday 17 October 2025Time: 3 pm Venue: AT 101
Energetic feedback from massive stars with low abundances of heavy elements ("metals") regulates the evolution of low-mass galaxies, both nearby and in the early Universe. To understand those processes requires robust models of massive star formation, evolution, and ionizing photon production at low metallicity. Yet, these models remain largely theoretical and uncertain due to a lack of observational constraints in metal-poor galaxies close enough that individual stars and star-forming gas can be spatially resolved.
I will present new insights into the astrophysics of individual metal-poor stars in the nearby Universe from large observational surveys with the Hubble Space Telescope and some of the world's largest ground-based observatories. I will then describe the recent discovery of molecular gas in a very low-metallicity, star-forming galaxy with James Webb Space Telescope, which provides a novel constraint on the nature of the metal-poor gas from which stars formed in the early Universe. These detailed observations that can only be made in very nearby galaxies are essential to guide the massive-star models that astronomers rely on to interpret observations of distant, metal-poor galaxies and their impact on the evolution of the early Universe.
Gravitational wave analysis with machine learning
Maximilian DaxUniversity of TuebingenDate: Friday 24 October 2025Time: 3 pm Venue: AT 101Gravitational-wave (GW) astronomy promises groundbreaking discoveries in the coming decades, but its progress is bottlenecked by the computational challenges of large-scale and real-time data analysis. I will present a machine learning (ML) approach for fast and accurate GW inference that addresses these challenges. This work combines simulation-based inference, generative modeling, equivariant ML, and classical sampling techniques. I will demonstrate how ML enables new scientific capabilities in GW astronomy and, conversely, how the demands of this domain drive fundamental innovations in ML, with applications beyond astrophysics.
Reaching and Teaching Neurodivergent Learners in STEM: Strategies for Embracing Uniquely Talented Problem Solvers
Jodi Asbell-ClarkeSaint Mary's UniversityDate: Friday 31 October 2025Time: 3 pm Venue: AT 101
Our society is facing enormous STEM challenges, and we need problem solvers who are creative and systematic, who pay close attention to details, and who remain persistent until a problem is solved. We have these talented thinkers among us. They often identify as neurodivergent, be it autistic, dyslexic, and/or ADHD. Neurodivergent learners all too often they are treated as “broken” and needing to be “fixed” in our educational systems, rather than seen for their unique brilliance and potential. My book, Reaching and Teaching Neurodivergent Learners in STEM: Strategies for Embracing Uniquely Talented Problem Solvers (Routledge/Taylor & Francis, 2023) considers how neurodiversity—the different ways people learn and think—may present an exciting opportunity to build an innovative STEM workforce. Drawing from thirty years of collaboration with educators, learners, and STEM professionals; I have integrated a rich set of stories and strategies regarding neurodiversity in STEM, illustrating theories from research from psychology, education, and neuroscience. My talk will summarize this work and foster a discussion about how neurodiversity overlaps with many of the problem-solving skills needed in STEM.
Neutrinos and the Dark Universe: Peering into the Unknown with Liquid Argon detectors
Michela LaiQueen's U/UCRDate: Friday 7 November 2025Time: 3 pm Venue: Burke Theatre A
Beyond the dripline: neutron-unbound systems, MoNA-LISA, and Virginia State University
Thomas RedpathVirginia State UniversityDate: Friday 21 November 2025Time: 3 pm Venue: AT 101
Modern efforts to study the atomic nucleus have reached an exciting juncture with the construction of the Facility for Rare Isotope Beams (FRIB). At the heart of this facility is a linear accelerator that will boost long-lived nuclei to high speeds after which they will be directed onto a target where nuclear collisions inside the target atoms will fragment the beam nuclei into lighter, short-lived, exotic nuclei. These reaction products are still moving fast enough to be directed via magnets to any of several different experimental setups in less than a millionth of a second.
The Modular Neutron Array (MoNA) has been incorporated into one of the experimental stations. In the current setup, the array consists of 144 bar-shaped plastic scintillator detectors, each measuring 200 centimeters long, 10 centimeters wide, and 10 centimeters high. These detectors are used in experiments to measure neutron-unbound systems which are a special type of exotic nuclei. These systems are produced in nuclear reactions between high-speed exotic nuclei produced from the accelerator and nuclei in a second target positioned a few meters from the MoNA setup. They decay as soon as they’re produced by emitting one or more neutrons, and MoNA is designed to detect these neutrons. Careful measurements of the neutrons and residual nucleus help scientists reconstruct information about the original, quickly decaying neutron-unbound system. Measuring the properties of various neutron-unbound systems is important for understanding how nuclear properties change and evolve from stable to exotic nuclear systems. This understanding is crucial to building a coherent picture of the dynamic system that is the atomic nucleus. This talk will discuss some of the ongoing projects that involve undergraduate students at Virginia State University in collaborative research between the VSU Nuclear Science Laboratory, the MoNA Collaboration, and FRIB.
Detection and characterization of hot dust in AGN tori using Near Infrared data
Gaia GasparSaint Mary's UniversityDate: Friday 28 November 2025Time: 3 pm Venue: AT 101
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Magnetic star-planet interaction
Ekatarina IlinASTRONDate: Friday 26 September 2025Time: 3 pm Venue: AT 101
The past decade has revealed that exoplanets are abundant. The evolution of their atmospheres over cosmic timescales is the next great frontier in our understanding of those planets. Star-planet interactions can determine the long-term stability and survival of planetary atmospheres. This interaction occurs in one direction, where stellar high-energy radiation and particles gradually erode the planetary atmosphere. However, recent evidence shows that the reverse is also possible: A planet in a sufficiently close orbit can influence its host star through magnetic interactions. In this talk, I will review what we know and don't know about the magnetic ways in which planets perturb their host stars, and explore the potentially destructive repercussions for these planetary troublemakers.
Properties of nuclear star clusters in 41 dwarf galaxies from the MATLAS survey and implications on their formation
Melina PoulainUniversity of OuluDate: Friday 12 September 2025Time: 3 pm Venue: AT 101
Debated for decades, the formation of nuclear star clusters (NSCs) --the densest stellar objects in the Universe-- currently opposes two main scenarios: the migration and merging of globular clusters (GCs) due to dynamical friction, and the in-situ star-formation from gas infall. Studies of NSC stellar populations suggest that the former prevails in dwarf galaxies, with a possible contribution of the latter. However, timescales are such that up to now, no ongoing GC mergers were caught in the act. I will present a follow-up study of 41 nucleated dwarfs from the MATLAS survey observed with the high resolution ACS camera of the Hubble Space Telescope. About 12% of the galaxies show a complex nuclear region containing multiple star clusters and stellar tails which, I will show, establish a first direct evidence of ongoing star cluster mergers in the center of dwarf galaxies. Structural properties and photometry of the full NSC sample have been derived and compared to NSCs from galaxies in a range of mass and environment. I will showcase the results and discuss them in terms of NSC formation process. I will conclude on the future of NSC studies in the context of upcoming large surveys with deep and high spatial resolution observations, such as the Euclid Wide Survey.
Direct imaging spectroscopy of exoplanets with JWST
Kielan HochSTSciDate: Friday 19 September 2025Time: 3 pm Venue: AT 101
JWST has opened the door to spectroscopy of directly imaged exoplanets beyond 3 microns, offering a new landscape for measuring their fundamental and atmospheric properties. Directly imaged planets are in a stage of early evolution and are undergoing atmospheric processes that are critical for understanding planetary atmospheric evolution and formation. These planets, with masses of ~2-14MJup and temperatures of ~500-2000 K, remain a mystery for planet formation models—core accretion and gravitational instability. Observations that probe elemental abundances in their atmospheres can shed light on their formation. Here I present JWST Cycle 1 programs that have pioneered the use of JWST’s NIRSpec IFU to obtain spectra of substellar companions close to sunlike stars. For HD 19467 B, NIRSpec spectra show detections of CO, CO2, CH4, and H2O. We forward model the R~2,700 spectra using custom PHOENIX atmospheric model grids to constrain the abundances of these molecules, the C/O ratio, and non-equilibrium chemistry. These results highlight a need for revisions of disequilibrium chemistry models to vary the CO2 abundance with the new spectral information provided by NIRSpec. For the multi planet system YSES-1, my team obtained one of the most comprehensive datasets of a multi-planet system with spectral coverage from 1-12 microns using NIRSpec and MIRI. The spectra allow direct spectral comparison of sibling planets in unprecedented detail with spectra that show the first direct detection of silicate clouds in an exoplanet YSES-1 c and the detection of a circumplanetary disk around YSES-1 b with olivine emission that could be caused by formation of larger bodies such as moons.
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