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This is a List of Talks Lists that is a List of all IoA Seminars, Colloquia, Extra talks, IoA Stellar Pops and Extragalactic Gathering, etc. It is used as a feed for the IOA website and Digital Display screens. Individual Talks should NOT be added to this Talk lists. They should be added to one of the series that feed this list.
Updated: 34 min 32 sec ago

Thu 15 May 16:00: Title to be confirmed

Tue, 29/04/2025 - 13:01
Title to be confirmed

Abstract not available

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Fri 09 May 11:30: How do the most luminous black holes accrete and expel gas?

Mon, 28/04/2025 - 15:16
How do the most luminous black holes accrete and expel gas?

The gravitational pull of a black hole attracts gas and forms an accretion disk where the interplay between hydromagnetic processes and the warping of space-time releases gravitational energy in the form of radiation, relativistic jets, and winds. Most gas falls into supermassive black holes when the accretion rate approaches the Eddington limit (L=Ledd), at which point radiation pressure overcomes gravity. To date, our knowledge of such `luminous’ black hole accretion disks mostly relies on semi-analytical models, supplemented by a limited set of numerical simulations. In my talk I will discuss new insights gained from state-of-the-art radiative general relativistic magnetohydrodynamics (GRMHD) simulations of accretion near the Eddington limit such as the formation of a hot corona, disk truncation, and other physical processes driving the spectral evolution of luminous black holes. I will finish my talk by discussing the challenges and opportunities the next-generation of GRMHD simulations will bring in developing a comprehensive understanding of black hole accretion across the luminosity spectrum.

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Thu 01 May 16:00: Irradiated brown dwarfs

Mon, 28/04/2025 - 11:25
Irradiated brown dwarfs

Brown dwarfs are often described as failed stars, however the flip side of this description is that they can also be described as over-ambitious planets. With masses between 13-70 Jupiter masses they have cool atmospheres dominated by cloud features, molecules and show features due to weather. These atmospheres have a lot of similarities with atmospheres we see in planets in our solar system, and also directly imaged exoplanets. The question then is: How like hot Jupiters are irradiated brown dwarfs? In this seminar I will describe the known irradiated brown dwarfs and how they evolve into post-common envelope systems containing a white dwarf. These rare binaries have very short periods (~hrs) and the brown dwarf is irradiated by the white dwarf companion, often with large amounts of UV radiation. I will discuss the atmospheres of these highly irradiated brown dwarfs and their similarities with irradiated exoplanets.

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Wed 30 Apr 13:15: Rebirth of the Ancients: Globular Clusters in Their Renaissance Era

Fri, 25/04/2025 - 13:57
Rebirth of the Ancients: Globular Clusters in Their Renaissance Era

Globular clusters (GCs) are multi-faceted cosmic tracers, currently experiencing a renaissance and resurgence of interest in both their formation mechanisms and their role in global galaxy evolution. In the context of galaxy formation and evolution, the importance of GCs in the earliest stages of galaxy assembly continues to grow. Observations of massive bound clusters at the epoch of reionization and extreme nitrogen enhancement at 𝑧 = 11 are two recent examples from JWST that hint at the significance of GCs in the growth of the earliest galaxies. Meanwhile, the discovery that 50% of ancient, in-situ Milky Way stars are nitrogen-enhanced directly connects GCs to the field of Galactic Archaeology. The local population of Milky Way globular clusters represents a unique set of objects for which age, chemical abundances, and dynamical properties can all be determined with exceptionally high precision (on the order of 1–5%), providing critical insights into galaxy formation and evolution across cosmic time. Over the course of this talk, I will discuss several ways in which we have advanced our understanding of GC formation and gained insight into rare nucleosynthetic sites in early dwarf galaxies. I will also present dynamical results that show how the Milky Way GC population serves as a sensitive probe of our Galaxy’s growth, and I will share some very recent findings that use GC ages to project the Milky Way back in time—placing it in context with star-forming galaxies at 𝑧 = 3.

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Tue 29 Apr 13:00: Formation of planetary cores in spontaneously generated dust traps during the secular evolution of magnetized protoplanetary disks

Fri, 25/04/2025 - 03:32
Formation of planetary cores in spontaneously generated dust traps during the secular evolution of magnetized protoplanetary disks

An outstanding gap in the current planet formation theory is about the first steps of the planet formation process; namely how, when and where the initially ISM like solid dust particles grow into pebbles and planetesimals, the building blocks of planetary cores. Protoplanetary disks provide the initial conditions for the planet formation process. They are weakly magnetized accretion disks that are subject to the magnetorotational instability (MRI), one of the main magnetized processes responsible for their angular momentum transport and gas turbulence. The nonideal magnetohydrodynamic (MHD) effects prevent the MRI from operating everywhere in PPDs, leading to a complex dichotomy between MRI active regions with higher gas turbulence and non-MRI regions with lower gas turbulence. In this talk,  I will present the first numerical framework that describes the evolution of PPDs over millions of years powered by the MRI . It captures the MRI driven gas evolution via nonideal MHD calculations, which accounts for the dynamics and growth of the solid dust particles. An MRI powered mechanism that can spontaneously generate short- and long-lived pressure maxima in the PPD is unveiled. Within the long-lived pressure maxima, solid dust particles can be efficiently trapped, grow into pebbles, and reach high enough dust-to-gas mass ratios to potentially trigger the formation of planetesimals via the streaming instability. These planetesimals and pebbles can further rapidly interact to form planetary cores.

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Fri 23 May 11:30: Between the extremes -- the physics of the first stars, galaxies, and black holes

Tue, 22/04/2025 - 13:36
Between the extremes -- the physics of the first stars, galaxies, and black holes

The emergence of the first sources 13.6 billion years ago had a profound effect on the Universe, initiating its last major phase-change and ending the so-called Cosmic Dark Ages. Unlocking the physics of those primordial sources thus represents a fundamental step towards a comprehensive understanding of the initial conditions that formed the building blocks for the Universe we see today. While Hubble painted a fairly straight forward picture, early JWST data revealed an infant Universe far more remarkable and exotic than previously thought, with hyper-luminous galaxies detected out to z=14, chemically-enriched and Nitrogen-enhanced interstellar media out to z=12, and apparently over-massive black holes to z=10. Are these sources representative of the global population, or do they reflect peculiar objects at a particular evolutionary phase? In this talk I will present efforts to address these questions through the spectroscopic study of statistical samples of high-redshift (z>5-14) galaxies with JWST /NIRSpec, establishing a benchmark for their chemical enrichment journeys, ISM conditions, (re)ionizing capabilities, and spectroscopic fingerprints. Additionally, I will showcase the importance of utilizing unbiased samples of galaxies to gain representative insight into the ISM conditions and evolutionary pathways of the most luminous populations uncovered by JWST .

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Fri 30 May 11:30: Chasing the Light: Shadowing, Collimation, and the Rapid Growth of Infant Black Holes

Mon, 21/04/2025 - 12:40
Chasing the Light: Shadowing, Collimation, and the Rapid Growth of Infant Black Holes

Observations with the James Webb Space Telescope (JWST) have uncovered a substantial population of high-redshift broad-line active galactic nuclei (AGNs) characterized by moderate luminosities, weak X-ray emissions, and faint high-ionization lines, challenging conventional models of AGN activity. In this talk I will propose that these sources are accreting at super-Eddington rates, and discuss how such accretion flows, shaped by thick disk geometries and anisotropic radiation fields, may provide new insights into black hole growth in the early Universe.

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Fri 16 May 11:30: Towards understanding the epoch of reionization out to the cosmic dawn

Fri, 18/04/2025 - 08:54
Towards understanding the epoch of reionization out to the cosmic dawn

Work on understanding the epoch of reionization has been galvanized in recent years by a series of observational and theoretical breakthroughs. These include the recognition that spatial structure in the Lyman-α forest retains signatures of reionization history, the discovery of galaxies and quasars deep in the reionization era by JWST , and renewed efforts to detect the redshifted 21-cm signal from cosmic dawn and the epoch of reionization. In this talk, I will present a series of results from our group that address the goal of understanding the evolving ionization state of the Universe, from cosmic dawn to the final stages of reionization. This includes new simulations of reionization, updated measurements of the mean free path of ionizing photons, improved constraints on the neutral hydrogen fraction from quasar damping wings, and interpretations of AGNs and LAEs discovered by JWST . I will describe our ongoing attempts to directly detect the neutral parts of the IGM for the first time using the 21-cm forest, and discuss the implications of JWST data for quasar growth during this era. Deeper into the reionization epoch, I will present new approaches to charting reionization using LAEs. Closer to cosmic dawn, I will highlight new radiative transfer models of Lyman-α coupling and a model-agnostic framework for combining JWST and 21-cm observations, including results from REACH . I will conclude by reviewing where we are and outlining key challenges ahead.

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Tue 15 Apr 11:00: Growing pains: the dining habits of stars, planets and black holes

Mon, 14/04/2025 - 12:24
Growing pains: the dining habits of stars, planets and black holes

To make planets, stars and supermassive black holes, one must rapidly accrete material onto central objects. But the tiniest tangential motion combined with angular momentum conservation sends material into orbit, rather than accreting. Since work at the IoA in the 1970s we have understood that Nature solves the angular momentum problem by forming accretion discs, but the angular momentum transport mechanism remains unclear. The past 10 years have given us spectacular resolved observations of discs around both young and old stars, bringing fresh clues. In this talk I’ll explain how pairing 3D simulations with observations helps us solve the problem of accretion, revealing how stars and planets form, black holes grow and how accretion powers tidal disruption events.

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Fri 09 May 11:30: How do the most luminous black holes accrete and expel gas?

Thu, 10/04/2025 - 11:40
How do the most luminous black holes accrete and expel gas?

The gravitational pull of a black hole attracts gas and forms an accretion disk where the interplay between hydromagnetic processes and the warping of space-time releases gravitational energy in the form of radiation, relativistic jets, and winds. Most gas falls into supermassive black holes when the accretion rate approaches the Eddington limit (L=Ledd), at which point radiation pressure overcomes gravity. To date, our knowledge of such `luminous’ black hole accretion disks mostly relies on semi-analytical models, supplemented by a limited set of numerical simulations. In my talk I will discuss new insights gained from state-of-the-art radiative general relativistic magnetohydrodynamics (GRMHD) simulations of accretion near the Eddington limit such as the formation of a hot corona, disk truncation, and other physical processes driving the spectral evolution of luminous black holes. I will finish my talk by discussing the challenges and opportunities the next-generation of GRMHD simulations will bring in developing a comprehensive understanding of black hole accretion across the luminosity spectrum.

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Tue 15 Apr 11:00: Growing pains: the dining habits of stars, planets and black holes

Wed, 09/04/2025 - 15:30
Growing pains: the dining habits of stars, planets and black holes

To make planets, stars and supermassive black holes, one must rapidly accrete material onto central objects. But the tiniest tangential motion combined with angular momentum conservation sends material into orbit, rather than accreting. Since work at the IoA in the 1970s we have understood that Nature solves the angular momentum problem by forming accretion discs, but the angular momentum transport mechanism remains unclear. The past 10 years have given us spectacular resolved observations of discs around both young and old stars, bringing fresh clues. In this talk I’ll explain how pairing 3D simulations with observations helps us solve the problem of accretion, revealing how stars and planets form, black holes grow and how accretion powers tidal disruption events.

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Mon 02 Jun 16:00: Imaging and Design with Differentiable Physics Models

Wed, 09/04/2025 - 04:24
Imaging and Design with Differentiable Physics Models

Abstract not available

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Mon 02 Jun 16:00: Title to be confirmed

Tue, 08/04/2025 - 18:27
Title to be confirmed

Abstract not available

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Fri 11 Apr 11:30: Unveiling AGN Outflows: A High Resolution Morphological Study with LOFAR-VLBI

Fri, 04/04/2025 - 16:27
Unveiling AGN Outflows: A High Resolution Morphological Study with LOFAR-VLBI

How AGN (Active Galactic Nuclei) feedback operates is one of the unsolved mysteries plaguing modern day astronomy. AGN outflows could explain how this feedback operates and, to investigate this, I use the [O III ] emission line as a tracer of ionised outflows. In this talk, I will present work investigating the link between low-frequency radio emission, using the LOFAR Two-meter Sky Survey Deep Fields at 144 MHz, and [O III ] kinematics, measured from SDSS spectroscopy, for a sample of optically selected AGN . We discover that radio detected AGN are more likely to host an [O III ] outflow compared to radio non-detected AGN . We observe a stronger broad, blue-shifted component in the radio-detected AGN , implying a profound link between low-frequency radio emission and [OIII] outflows. To further link AGN outflows to low-frequency radio emission, we harness the power of widefield VLBI (Very Long Baseline Interferometry) processing and imaging by incorporating the international stations of LOFAR into the data reduction process, to obtain sub-arcsecond radio images. To conclude this talk, I will present the first 0.3” resolution image at 144 MHz of the Boötes Deep Field and early results linking high resolution radio morphologies at 144 MHz to the presence of [O III ] outflows.

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Thu 03 Apr 10:00: Latest upper limits on 21 cm power spectrum using MWA observations

Tue, 01/04/2025 - 09:45
Latest upper limits on 21 cm power spectrum using MWA observations

We present the deepest upper limits achieved by the Murchison Widefield Array to date at redshifts z=6.5, z=6.8, and z=7. This study is based on observations centred at (RA = 0h, DEC = −27°), collected between 2013 and 2021. The analysis builds upon the systematic framework developed in Nunhokee et al. (2024), which employs intermediate data products for data quality assessment to minimise contamination in the targeted power spectrum region. The final power spectra are constructed from 221 hours of observations for z=6.5 and 226 hours for z=6.8 and z=7.0, using the Cosmological HI Power Spectrum Estimator. Our results provide the first evidence of a heated intergalactic medium (IGM) at redshifts z=6.5 to z=7.0. Additionally, I will discuss how these results can be improved by refining the separation of thermal noise and systematics from foregrounds, leveraging fluctuations in the probability distributions of the power spectra (Trott et al.,submitted).

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Thu 10 Apr 11:30: Probing Black Hole Winds with SimBAL: Mapping the Physics of Broad Absorption Line Quasar Outflows KICC Special Seminar

Mon, 31/03/2025 - 14:10
Probing Black Hole Winds with SimBAL: Mapping the Physics of Broad Absorption Line Quasar Outflows

Broad absorption line (BAL) quasars provide striking evidence of energetic winds driven by accreting supermassive black holes. These outflows are thought to play a crucial role in regulating black hole growth and the host star formation rate, as well as shaping the evolution of galaxies; however, their physical properties—such as radius and energetics—remain poorly constrained. Our group has developed SimBAL, a spectral synthesis tool that enables detailed, physically motivated modeling of BAL quasar spectra. It has allowed us to perform a detailed spectral analysis of a large sample of BAL quasars for the first time and to characterize multi-phase outflows in a quasar discovered at the Epoch of Reionization. I will demonstrate SimBAL’s unique strengths by discussing the results from several projects and how our group has taken a systematic approach to investigate the physics of black hole winds. Lastly, I will introduce the 4MOST–Gaia Purely Astrometric Quasar Survey, an upcoming spectroscopic survey uniquely designed to deliver the first large-scale, color-independent quasar reference sample.

KICC Special Seminar

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Thu 10 Apr 11:30: Probing Black Hole Winds with SimBAL: Mapping the Physics of Broad Absorption Line Quasar Outflows KICC Special Seminar

Mon, 31/03/2025 - 08:53
Probing Black Hole Winds with SimBAL: Mapping the Physics of Broad Absorption Line Quasar Outflows

Broad absorption line (BAL) quasars provide striking evidence of energetic winds driven by accreting supermassive black holes. These outflows are thought to play a crucial role in regulating black hole growth and the host star formation rate, as well as shaping the evolution of galaxies; however, their physical properties—such as radius and energetics—remain poorly constrained. Our group has developed SimBAL, a spectral synthesis tool that enables detailed, physically motivated modeling of BAL quasar spectra. It has allowed us to perform a detailed spectral analysis of a large sample of BAL quasars for the first time and to characterize multi-phase outflows in a quasar discovered at the Epoch of Reionization. I will demonstrate SimBAL’s unique strengths by discussing the results from several projects and how our group has taken a systematic approach to investigate the physics of black hole winds. Lastly, I will introduce the 4MOST–Gaia Purely Astrometric Quasar Survey, an upcoming spectroscopic survey uniquely designed to deliver the first large-scale, color-independent quasar reference sample.

KICC Special Seminar

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Fri 04 Apr 11:30: The first stars: window to cosmic dawn

Fri, 28/03/2025 - 18:09
The first stars: window to cosmic dawn

The era of cosmic dawn began with the first stars that formed in the Universe a mere 200 – 300 million years after the Big Bang. These stars produced the first supernovae and black holes, enriched the interstellar medium (ISM) with metals, were the building blocks of the first galaxies, and significantly contributed to cosmic reionization. However, compared to star formation and feedback in metal-rich environments today, the lack of direct observations at low metallicities as well as high redshifts has posed a significant challenge for understanding the physics behind their formation and evolution. In this talk, I will introduce POPSICLE , a new framework for high resolution simulations that caters to star formation and feedback in low metallicity ISM reminiscent of redshift > 10 galaxies. I will describe how incorporating the full spectrum of ISM physics coupled to stellar evolution is crucial to constrain the stellar initial mass function (IMF) and feedback in such environments. I will particularly focus on Population III stars, and discuss their potential as seed black holes in the early Universe. I will conclude by showcasing the capability of GPU -accelerated simulations to revolutionize our understanding of the astrophysics of cosmic dawn, and to bring theory at par with state of the art observations from JWST .

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