Next Wednesday Seminars

The Great Oxidation Event (GOE) was a 200 Myr transition circa 2.4 billion years ago that converted the Earth’s anoxic atmosphere to one where molecular oxygen (O2) was abundant. This rise in O2 is thought to have substantially throttled hydrogen (H) escape and the associated water (H2O) loss. In this study we use WACCM6 , a three-dimensional Earth System Model to simulate Earth’s atmosphere and predict the diffusion-limited escape rate of hydrogen due to varying O2 concentrations based on atmospheric estimations from the GOE onward, ranging between 0.1 PAL to 150 PAL , where PAL is the present atmospheric level of 21 % by volume. O2 indirectly acts as a control valve on the amount of hydrogen atoms reaching the homopause in the simulations: less O2 leads to decreased O3 densities, reducing local temperatures by up to 5 K, which increases H2O freeze-drying. For the considered scenarios, the maximum difference in the total H mixing ratio at the homopause and calculated diffusion-limited escape rates is a factor of 3.2 and 4.7, respectively, with the prescribed CH4 mixing ratio setting a minimum diffusion escape rate of ≈ 2 × 10^10 mol H/yr. These numerical predictions support geological evidence that the majority of Earth’s hydrogen escape occurred prior to the GOE .

• Speaker: Greg Cooke / IoA
• Tuesday 06 May 2025, 13:15-13:40
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: .

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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.

• Speaker: Stephanie Monty / IoA
• Wednesday 30 April 2025, 13:15-13:40
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: .

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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.

• Speaker: Daniel Price, Monash University
• Tuesday 15 April 2025, 11:00-12:00
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Cristiano Longarini.

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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.

• Speaker: Daniel Price, Monash University
• Tuesday 15 April 2025, 11:00-12:00
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Cristiano Longarini.

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Protoplanetary discs are the place in which planets form and evolve, and the reservoir from which protostar accrete material. The presence of a perturber whether a planet or a stellar companion and its interaction with the parental disc play a crucial role in shaping the dynamics and evolution of the system, generating substructures such as gaps, rings and asymmetries routinely observed with different tracers in discs (large mm dust and gas with ALMA , small micrometric dust with VLT ).

However, characterizing these systems remains challenging: the only two planetary companions unambiguously detected, PDS70b and c, lie in a wide and open cavity of the same object, and once the perturber is a star, massive and wide enough to be detected, characterize the binary orbit is challenging due to the timescales at play.

In this talk, I will show new results to address and mitigate these issues. Firstly, I will show new results from the astrometry and the hydrodynamical models of GG Tau A, a multiple stellar system where the orbits of the stars is still not fully constrained. Then, I will discuss how the advent of the Extremely Large Telescope (ELT), with its first light imager MICADO /MORFEO, will revolutionize the field, providing high angular resolution images that will allow us to detect embedded protoplanets and small-scales substructures.

• Speaker: Claudia Toci / European Southern Observatory
• Wednesday 19 March 2025, 13:40-14:05
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: .

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In the standard cosmological model, cold dark matter gives rise to small-scale structure problems which Warm Dark Matter (WDM) in the keV range may address. Previous studies have narrowed the mass range for WDM , but further testing is increasingly challenging due to resolution limits of current spectrographs. Given the lack of success in laboratory dark matter searches, an intriguing alternative has recently re-emerged—a mixed dark matter scenario that combines cold and warm components, known as Cold+Warm Dark Matter (CWDM). In this framework, structure formation is influenced by the free-streaming of the warm component at the small scales probed by the Lyman-α forest, requiring hydrodynamical simulations to account for non-linear structure evolution and gas dynamics.

This presentation focuses on updated constraints on CWDM derived from high resolution and high-redshift (z=4.2−5.0) spectra from UVES and HIRES spectrographs. We use the 1D flux power spectrum to compare simulated Lyman-α forest to observational data in a Bayesian inference framework. The grid of simulations spans a high-dimensional parameter space, which we efficiently sample by implementing a neural network emulator at the likelihood level.

Beyond 1D clustering statistics, these allowed mixed dark matter models can accommodate small-scale deviations in the high-k regime of the matter power spectrum, potentially alleviating the S8 tension.

• Speaker: Olga Garcia Gallego / IoA
• Wednesday 19 March 2025, 13:15-13:40
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: .

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We’ll explore the key findings from the recent IoA staff neurodiversity survey. We’ll celebrate the positive experiences shared by participants and shine a light on some of the challenges. The session will address some comments raised in the survey, while also outlining the focus group’s priorities as we move forward.

• Speaker: Lalitha Sairam, IoA
• Wednesday 12 March 2025, 13:40-14:05
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Cristiano Longarini.

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Astronomy is a heavily visual science. Outreach and education typically rely on beautiful images of the sky, and the communication of research findings in papers and talks revolves around figures. These visual media, while beautiful and effective for many audiences, have historically excluded blind and low vision people from engaging with astronomy. How can we work together towards science that is more inclusive of blind people and people with disabilities more broadly? In this talk, I will discuss accessibility in astronomy, particularly for the blind and low vision community. Topics will include the new HTML paper format on arXiv, writing alternative (alt) text for figures, and some best practices for organizing and attending conferences. Some general background on disability and assistive technology will also be discussed.

• Speaker: Sarah Kane, IoA
• Wednesday 12 March 2025, 13:15-13:35
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Cristiano Longarini.

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As the most massive gravitationally bound structures in the Universe, galaxy clusters frequently act as strong gravitational lenses. Strong lensing (SL) enables us to reconstruct the total mass distribution of a cluster with extreme accuracy, providing insights into the physical properties of dark matter and its interplay with baryons. SL models are also crucial for studying magnified high-redshift sources and measuring cosmological parameters from observed time delays between lensed variable sources. However, the accuracy of SL models is limited by parametric degeneracy, which hinders the reconstruction of the mass distribution of cluster members. This degeneracy can be resolved using independent information from their stellar kinematics. After a general introduction to SL by galaxy clusters, I will present how we leveraged deep MUSE /VLT observations of SL clusters to build a large catalogue of accurate stellar velocity dispersion measurements of early-type member galaxies. These measurements serve as the foundation for calibrating new scaling relations that describe their structure in a set of highly accurate SL models and for comparisons with cosmological hydrodynamical simulations of galaxy clusters, aimed at testing the ΛCDM paradigm.

• Speaker: Giovanni Granata / University of Portsmouth
• Monday 03 March 2025, 13:40-14:05
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: .

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With the recent discovery of quiescent galaxies at z>3, studying of dusty star-forming galaxies at high redshift became more vital than ever, as they are thought to be precursors of quiescent galaxies. However, until the launch of JWST , studying the rest-frame of optical emission of these sources at redshifts higher than 3 was out of reach of astronomers, often solely relying on the ALMA observations of their FIR emission lines. In this talk, I will present one of the first JWST /NIRSpec IFS data of a massive dusty star-forming galaxy at the Epoch of Reionisation. COS -3018, is a unique UV bright galaxy (LUV>2 L*) at z~6.8, previously only observed using ALMA ([CII]158 microns, [OIII] 88 microns), VLT X -Shooter (Lyman-alpha) and HST broadband photometry. Furthermore, this galaxy has a large amount of dust (log Mdust =10.7 Msol) and an excess of [OIII]88micron emission suggesting that this might be an AGN or has non-standard ISM conditions such as AGN . I will present deep high-resolution JWST /NIRSpec IFS observations of rest-frame UV and optical continuum and emission lines, in combination with deep ALMA [CII] and [OIII]88micron observations and NIR Cam photometry. Using the deep and unique NIR Spec IFS (PRISM+R2700) observations, I will show the ISM conditions in this unique galaxy: excitation conditions (extreme star formation or AGN ?), metallicity gradient, location of dust obscured (from ALMA high resolution observations) and unobscured star formation. Finally, I will answer the question: What is driving such an extreme production of dust in this galaxy and UV luminosity in this galaxy?

• Speaker: Jan Scholtz / IoA
• Monday 03 March 2025, 13:15-13:40
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: .

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Substructures in protoplanetary discs have long been hypothesised to act as sites of planetesimal formation, where dust particles can collide and grow to macroscopic sizes. In this talk, I will consider the substructures formed when a protoplanetary disc is perturbed by an unbound stellar companion (a stellar flyby). I will present the results of 3D hydrodynamical simulations of discs after a range of flyby encounters, and employ a novel particle tracking algorithm to study the fate of dust particles in the flyby-induced rings and spirals. Our results show that stellar flybys could trigger planetesimal formation in protoplanetary discs.

• Speaker: Vasundhara Prasad / IoA
• Wednesday 19 February 2025, 13:15-13:40
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: .

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The oldest, most metal-poor stars we find in the Milky Way today were born in pristine environments in the early Universe. These local, ancient stars contain unique clues about the First Stars and the early formation and evolution of our Galaxy. At low metallicity, many stars have been found to be enhanced in carbon, coming in two main types: some contain the fingerprints of the First Stars and others have experienced binary interaction with an evolved companion. I recently built a homogeneous sample of C-rich metal-poor stars using the Gaia XP spectra, employing a neural network and a dedicated training sample. I will present this recent paper and discuss how the change in frequency of C-rich stars with Galactic environment relates to globular clusters and clustered star formation in the early Universe.

• Speaker: Anke Ardern-Arentsen / IoA
• Wednesday 19 February 2025, 13:40-14:05
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Xander Byrne.

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The evolutionary pathways of protoplanetary disks differ depending on the surrounding environment. In massive star clusters, UV radiation affects disks via external photoevaporative winds, depleting the disks of their material and shortening their lifetimes. Known as proplyds, such irradiated disks are typically surrounded by a teardrop-shaped cloud of ionized gas and observed in forbidden emission lines.

While external photoevaporation of disks is unique to clusters such as the Orion Nebula Cluster (ONC), internal photoevaporative winds may be present in both high UV environments, and low-mass star forming regions with weak external UV fields. In the latter case, the winds arise due to radiation from the central star and can also be studied via forbidden line emission. It is therefore crucial to determine how to disentangle external winds from internal ones.

I will present the results based on the visually striking VLT /MUSE IFU data of a dozen proplyds in the ONC . This sample allows us to study the morphology of proplyds in a wealth of emission lines and determine their physical parameters. Among the results, I will present a proxy for unambiguously identifying externally driven winds with a forbidden line of neutral atomic carbon.

• Speaker: Mari-Liis Aru
• Wednesday 12 February 2025, 13:40-14:05
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Xander Byrne.

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The co-evolution of massive black holes and their host galaxies is well established within ΛCDM cosmology. The repeated mergers, accretion, and feedback that conspire to regulate this process can be studied in large-scale cosmological simulations, such as Illustris, FABLE , MillenniumTNG and Flamingo. These simulations resolve key galaxy formation processes at ~kpc scales, but are plagued with numerical inaccuracies at the smaller scales of black holes. This scale discrepancy presents significant challenges for investigating black hole properties and generating testable predictions, e.g. for future JWST , Gaia, LISA and IPTA observations of isolated and binary black holes. In this talk I will discuss the black hole population in FABLE . Our results show that the numerical treatment of black holes in cosmological simulations leads to a misleading picture, even at the well-resolved large scale of galaxies. In particular, a large fraction of black holes coalesce well before their host galaxies merge and thus require extra delays on the order of a few Gyrs. These delays, governed by the dynamical timescale of the merging host galaxies, occur before and in addition to any delays arising from unresolved ‘sub-grid’ physics describing BH hardening mechanisms on parsec scales. This effect has profound implications for the black hole merger rates predicted from these large-scale cosmological simulations as well as for the multi-messenger predictions, once black hole growth during these dynamical galaxy merger delays is accounted for.

• Speaker: Stephanie Buttigieg / IoA
• Wednesday 12 February 2025, 13:15-13:40
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Xander Byrne.

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It has long been established that the properties of type Ia supernovae (SNe Ia) depend on their local environment, even after typical standardisation methods. This is typically referred to as the mass step, where SNe Ia in high-mass galaxies are on average brighter than their low-mass counterparts post-standardisation, although trends have been established with other environmental properties including colour, specific star formation rate and distance from the centre of the galaxy. There has been ongoing debate in the field about whether these differences are intrinsic or just the result of extrinsic effects i.e. dust. I will present recent analysis of the environmental dependence of SNe Ia which have found an intrinsic contribution to the mass step, with particularly strong differences around the i-band secondary maximum. These results demonstrate that there are intrinsic differences between SNe Ia in different environments and raise an interesting question about what is driving these results; understanding this finding can help reveal the underlying physical cause of the environmental dependence of SNe Ia.

• Speaker: Matthew Grayling / IoA
• Wednesday 05 February 2025, 13:40-14:05
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Xander Byrne.

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Bright exoplanet host stars provide highly precise stellar and planetary parameters, as well as chemical abundances. However, modern multi-object spectroscopic surveys often neglect stars brighter than 11 visual magnitudes due to their relatively low on-sky number density, resulting in significant observational overhead. The WEAVE -TwiLight Survey (WTLS) will address this gap by employing a groundbreaking observing mode, that allows for observations of low-density/bright star fields, without compromising survey efficiency. With an input catalogue derived primarily from the northern PLATO long-duration phase field, WEAVE -TwiLight will result in a highly homogeneous spectral dataset, characterizing approximately 6,000 future PLATO targets, including 68 confirmed planet hosts. In this talk, I will present the progress made in implementing the new observing mode, alongside preliminary results from test observations obtained in late summer 2024, using WEAVE ’s high-resolution setup. Full-scale science operations for WEAVE -TwiLight are expected to begin in Q2 of 2025.

• Speaker: Thomas Hajnik / IoA
• Wednesday 05 February 2025, 13:15-13:40
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Xander Byrne.

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Ozone is a potential exoplanet biosignature due to its association with photosynthetically produced oxygen and strong absorption in the mid-infrared. However, the existence of ozone in Venus’s observable atmosphere, a planet with no known life, raises the possibility of ozone biosignature false-positives on Venus-like exoplanets. We use a photochemical model of Venus’s atmosphere to investigate the origin of its mesospheric ozone layer, and how similar ozone layers would manifest for Venus-like exoplanets. Our model shows that the hypothesis that Venus’s ozone forms on the nightside due to a flux of O radicals from the dayside, cannot generate enough ozone to match observed levels. Furthermore, we show that sufficient ozone cannot be produced by varying the surface chemistry, atmospheric thermal structure, or stellar flux in our model of Venus’s atmosphere, implying that a presently unknown chemical pathway is responsible for the ozone in Venus’s mesosphere. Until the origin of Venus’s ozone is understood, we cannot rule out that ozone production will be common on abiotic Venus-like worlds, a possibility that limits the usefulness of ozone as a biosignature.

• Speaker: Robb Calder / IoA
• Wednesday 04 December 2024, 13:15-13:40
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Xander Byrne.

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In hierarchical models of galaxy formation and evolution, galaxies grow through gas accretion and merger events. The tidal debris produced during these mergers serves as a fossil record of a galaxy’s assembly history, with characteristics that depend on the nature of the merger. Exploring these faint Low Surface Brightness (LSB) structures around galaxies of varying masses and environments is essential to fully understanding galactic evolution. Advances in dedicated instruments and data reduction pipelines from past, ongoing, and future surveys have significantly expanded our ability to explore the LSB Universe. In this talk, I will discuss how LSB features can be leveraged to investigate galactic growth, using deep imaging data from the Canada-France-Hawaii Telescope (CFHT) and ESA ’s Euclid space telescope, combined with an innovative online annotation tool.

• Speaker: Elisabeth Sola / IoA
• Wednesday 04 December 2024, 13:40-14:05
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Xander Byrne.

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Ozone is a potential exoplanet biosignature due to its association with photosynthetically produced oxygen and strong absorption in the mid-infrared. However, the existence of ozone in Venus’s observable atmosphere, a planet with no known life, raises the possibility of ozone biosignature false-positives on Venus-like exoplanets. We use a photochemical model of Venus’s atmosphere to investigate the origin of its mesospheric ozone layer, and how similar ozone layers would manifest for Venus-like exoplanets. Our model shows that the hypothesis that Venus’s ozone forms on the nightside due to a flux of O radicals from the dayside, cannot generate enough ozone to match observed levels. Furthermore, we show that sufficient ozone cannot be produced by varying the surface chemistry, atmospheric thermal structure, or stellar flux in our model of Venus’s atmosphere, implying that a presently unknown chemical pathway is responsible for the ozone in Venus’s mesosphere. Until the origin of Venus’s ozone is understood, we cannot rule out that ozone production will be common on abiotic Venus-like worlds, a possibility that limits the usefulness of ozone as a biosignature.

• Speaker: Robb Calder / IoA
• Wednesday 04 December 2024, 13:15-13:40
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Xander Byrne.

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The measurement of rotation curves led to big discoveries in astronomy, like the proposition of dark matter halos around galaxies. With the emergence of ALMA , it is now similarly possible to measure the rotation of gas in protoplanetary disks, which are several orders of magnitude smaller than galaxies. While the overall motion of the gas around newborn stars is Keplerian, with high spectral resolution molecular line observations, we can trace small-scale velocity perturbations caused by local pressure variations in the disk, possibly due to embedded planets. In the talk, I will discuss how we can observe gas rotation in planet-forming disks and what we can learn from studying the deviations from Keplerian rotation. In particular, I will present results from the rotation curve study for the disks of the exoALMA Large Program. We find that substructures in the deviation from Keplerian rotation are ubiquitous in our sample, on both small and large scales, and can reach up to 15 percent in the most extreme cases. Interestingly, the majority of the dust continuum rings and gaps are co-located with pressure maxima and minima, respectively. Finally, I will compare the presented results with the predictions from the theory and put them into the bigger picture of planet formation.

• Speaker: Joe Stadler / Observatoire de la Côte d’Azur
• Wednesday 27 November 2024, 13:40-14:05
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Xander Byrne.

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