The 2025 ANITA workshop will take place Monday - Wednesday, 3 - 5 February 2025 at the Mount Stromlo Observatory Visitor Centre.

• Schedule
• Participant list
• Abstract list

Schedule
Preliminary schedule, all times are AEDT.

Time	Monday, 3 February	Tuesday, 4 February	Wednesday, 5 February
9:15	Bus pickup from the Novotel	Bus pickup from the Novotel	Bus pickup from the Novotel
10:00 - 10:20	Hillary Davis HI Terminal Velocities in hydrodynamic N-body "surrogate" models of the Milky Way	Megha Sharma Binary collisions of stars by hypermassive black holes	Allan Ernest Gravitational Quantum Mechanical Effects on Galaxy Halo Composition: Predicting Gas Phase Fractions and Dark Matter Content
10:20 - 10:40	Sophie Young Absorption processes in young radio galaxies	Ilya Mandel Common envelope evolution, outcomes, and associated transients	Jack Nibbs The potential for circumbinary disc creation from weak common envelope interactions
10:40 - 11:00	Radhika Achikanath Chirakkara Magnetic field amplification in galaxy clusters with hybrid particle-in-cell simulations	Fiona Panther More than the sum of their parts: Resolving the boundary between black holes and neutron stars with post-merger gravitational waves	Mark Walker A simple framework for understanding the R Coronae Borealils stars
11:00 - 11:40	Morning coffee	Morning coffee	Morning coffee
11:40 - 12:00	Amrita Banerjee Does assembly bias have a role in AGN activity?	Fitz Hu How do tidal disruption events shine in optical and radio?	Claudia Reyes Acoustic modes in M67 cluster stars trace deepening convective envelopes
12:00 - 12:20	Darren Croton Cosmic dust as a dark matter discriminator	Aswathi Nair Discovering the origins of Gravitational wave sources - Double Neutron star edition	Evgeni Grishin Triple systems on the edge of chaos
12:20 - 12:40	Amit Seta Magnetic field scale in the interstellar medium of the Milky Way	Jordan Moncrieff Localising BBH mergers to AGN through spatial correlations	Alex Wallace Characterisation of Hidden Companions to Wobbling Stars
12:40 - 13:40	Lunch	Lunch	Lunch; ANITA Steering Committee Meeting
13:40 - 14:00	Truman Tapia Formation of ultra-diffuse galaxies and their globular cluster systems through mergers	Ryosuke Hirai Influence of companion stars on supernovae: the tale of SN2022jli	Daniel Price We're going planet hunting
14:00 - 14:20	Samuel Hansen Constraining radio AGN energetics and environments with the semi-analytic model RAiSE	Shun Cheung A search for deviations from general relativity in Gravitational-Wave Transient Catalogue 3: Reconstructing extra polarisations with a Gaussian Process	Discussion: stars and planets
14:20 - 14:40	Thomas Venville A search for dark matter annihilation from the Sagittarius Dwarf and Stream	Discussions: transients and gravitational waves	Discussion: stars and planets
14:40 - 15:00	Amanda Karakas The effect of mass loss and binary evolution on low metallicity AGB star yields	Discussions: transients and gravitational waves	Presentation of the J. P. Macquart Best Student Talk prize
15:00 - 15:40	Afternoon coffee	Afternoon coffee	Bus return to Novotel
15:40 - 16:00	Geoff Bicknell Jet-mediated AGN feedback in galaxy evolution	Mark Krumholz Displaced gamma-rays from Terzan 5 as a probe of cosmic ray transport
16:00 - 16:20	Kenny Chan Investigating Hierarchical Star Formation in the 30 Doradus Region and Orion Cluster	Jarrod Hurley OzSTAR and the future of supercomputing
16:20 - 16:40	Discussion: galaxies and AGN	Discussion: computing in Australia
16:40 - 17:00	Discussion: galaxies and AGN	Discussion: computing in Australia
17:10	Bus return to Novotel	Bus return to Novotel
19:00		Workshop dinner, Blu Ginger

Participant list

Name	Affiliation	Participating remotely?
Radhika Achikanath Chirakkara	Australian National University	N
Neelesh Amrutha	RSAA - ANU	Y
Jasmine Anderson-Baldwin	Swinburne University of Technology	N
Kateryna Andrych	Macquarie University	N
Amrita Banerjee	Swinburne University of Technology	N
Geoffrey Bicknell	Research School of Astronomy & Astrophysics, ANU	N
Amatul Firdausya Nur Cahyaningtyas	University of Melbourne	N
Kenny Chan	Macquarie University - Montana State University	N
Thippayawis (Tong) Cheunchitra	University of Melbourne	Y
Shun Cheung	Monash University	N
Darren Croton	Swinburne University of Technology	N
Hillary Davis	Sydney University	N
Wenhao (Eric) Dong	University of Melbourne	Y
Allan Ernest	Charles Sturt University	N
Smrithi Gireesh Babu	University of Sydney	Y
Evgeni Grishin	Monash University	N
Samuel Hansen	University of Tasmania	N
Miftahul Hilmi	The University of Melbourne	N
Ryosuke Hirai	Monash University/ RIKEN	N
Fitz Hu	Monash	N
Jarrod Hurley	Swinburne University of Technology	N
Ana Lourdes Juarez Garcia	Macquarie University	Y
Amanda Karakas	Monash University	Y
Sanja Lazarevic	Western Sydney University	Y
Ilya Mandel	Monash	N
Kayla Martin	Macquarie University	Y
Carmen Martinez Harris	Queensland University of Technology	N
Bridget Mcfarlane	Monash University	N
Samantha Mcivor	Queensland University of Technology	N
Melissa Mckenzie	Queensland University of Technology	N
Jordan Moncrieff	University of Western Australia	N
Ankita Mondal	Swinburne University of Technology	N
Huon Morton	Queensland University of Technology	N
Chunliang Mu	Macquarie University	Y
Haritha Mullathody	The University Of Melbourne	N
Ashwathi Nair	Swinburne University of Technology	N
Jack Nibbs	Macquarie University	N
Fiona Panther	University of Western Australia	N
Jason Price	ANU	N
Claudia Reyes	ANU	N
Jeff Riley	Monash University	N
Luke Rosier	University of Queensland	N
Ashley Ruiter	UNSW Canberra	N
Amit Seta	Australian National University	N
Megha Sharma	Monash University	N
Dennis Stello	UNSW Sydney	N
Janet Tang	RSAA, ANU	N
Truman Tapia	ICRAR	N
Cameron Taylor	University of Melbourne	N
Riley Thai	Monash University	N
Thomas Venville	RSAA, ANU	Y
Mark Walker	Manly Astrophysics	N
Alex Wallace	Monash University	N
James Watt	Australian National University	N
Karl Wette	Australian National University	N
Jordan Winstanley	University of Western Australia	N
Pavadol Yamsiri	The University of Sydney	N
Sophie Young	University of Tasmania	N
Ziqi Yuan	Macquarie University	N

Abstract list
Organised alphabetically by speaker surname.

Radhika Achikanath Chirakkara
Magnetic field amplification in galaxy clusters with hybrid particle-in-cell simulations
The intracluster medium of galaxy clusters is an extremely hot and diffuse, nearly collisionless plasma, which hosts dynamically important magnetic fields of ∼μG strength. Seed magnetic fields of much weaker strength of astrophysical or primordial origin can be present in the intracluster medium. In collisional plasmas, which can be approximated in the magnetohydrodynamical (MHD) limit, the turbulent dynamo mechanism can amplify weak seed fields to strong dynamical levels efficiently by converting turbulent kinetic energy into magnetic energy. However, the viability of this mechanism in weakly collisional or completely collisionless plasma is much less understood. In this talk, I will discuss the properties of the collisionless turbulent dynamo using three-dimensional hybrid-kinetic particle-in-cell simulations with the "AHKASH" code. We introduce turbulence driving, modelled using the Ornstein-Uhlenbeck process, in our Hybrid PIC code. To investigate steady-state turbulence with a fixed Mach number, it is important to maintain isothermal conditions, and we introduce a novel cooling method for PIC codes to achieve this. I will describe the properties of the collisionless turbulent dynamo in the kinematic regime for different values of the magnetic Reynolds number, initial magnetic-to-kinetic energy ratio, and initial Larmor ratio, i.e. the ratio of the Larmor radius to the size of the turbulent system. I will also discuss the distribution and evolution of the pressure anisotropy in the collisionless plasma and compare our results with the MHD turbulent dynamo. The nature of the collisional turbulent dynamo in the subsonic and supersonic regimes can differ significantly, as demonstrated by numerical MHD studies. I will present results on the features of turbulence and magnetic field amplification from the collisionless turbulent dynamo in both the subsonic and supersonic regime.

Amrita Banerjee
Does assembly bias have a role in AGN activity?
We compare the spatial clustering and physical properties of the active galactic nuclei (AGN) and star-forming galaxies (SFG) at fixed stellar mass using a volume-limited sample from the Sloan Digital Sky Survey (SDSS). The analysis of the two-point correlation function shows that the AGN are more strongly clustered than the SFG. The closer proximity to the 5th nearest neighbour for the AGN than that for the SFG indicates that AGN prefers the denser regions. We compare the distributions of the (u−r) colour, star formation rate (SFR), D4000 and concentration index of the AGN and SFG after matching their stellar mass distributions. The null hypothesis can be rejected at >99.99% confidence level in each case. The comparisons are also carried out at different densities. The differences persist at the same significance level in both the high and low-density regions, implying that such differences do not originate from the variations in the density. Alternatively stated, the AGN activity can be triggered in both the high and low-density regions. An analysis of the correlations between the different physical properties at fixed stellar mass reveals that the anticorrelations of SFR with morphology, colour and recent star formation history are 2−3 times stronger for the AGN than for the SFG. It suggests that the presence of a bulge and the availability of gas are the two most crucial requirements for AGN activity. We propose a picture where the galaxies at fixed stellar mass may have widely different assembly histories, leading to significant variations in bulge properties and cold gas content. Whether a galaxy of a given stellar mass can acquire the suitable conditions for AGN activity remains uncertain due to a broad diversity of assembly history. We conclude that AGN are stochastic phenomena owing to an underlying role of the assembly bias.

Geoff Bicknell
Jet-mediated AGN feedback in galaxy evolution
In this talk I shall review simulations of jets interacting with an inhomogeneous interstellar medium and the implications for the quenching of star formation through turbulence and related outflows.

Kenny Chan
Investigating Hierarchical Star Formation in the 30 Doradus Region and Orion Cluster
Around 150 globular clusters were discovered in the Milky way alone (Gianopoulos, 2023). Star formation becomes a hierarchical without a preferred scale. This is because their formation is also heavily driven by supersonic turbulence in the Interstellar matter (ISM) (Grasha et al., 2017). In the Magellanic Clouds alone and in the Milky Way, The age range across the star cluster population is very diverse, starting from just born to more than 10 Gyr (Martocchia et al., 2018). The star clusters’ distribution across the galaxies is not very smooth. Young star clusters tend to be mainly concentrated in spiral arms; old clusters are often found in galactic haloes (Pagnini et al., 2023). At the same time, binary clusters seem to be over-saturated inside the galaxies rather than just fractal formation (Goodwin and Whitworth, 2004). Fractal dimension of 30 Dor is a main focus. We now have the data to analyze the stars formation to prove whether frequency of binary clusters occurrence is true. This will help us understand better the true nature of star formation on a large scale. 30 Doradus is a great target for hierarchical star formation because the object is massive and an active star forming region (Sun et al., 2017). Analyzing of 30 Dor and Orion Cluster will be applicable to the entire LMC.

Shun Cheung
A search for deviations from general relativity in Gravitational-Wave Transient Catalogue 3: Reconstructing extra polarisations with a Gaussian Process
Gravitational waves predicted by general relativity only contain two polarisations: the plus and cross. However, alternate theories of gravity allow up to six polarisations, making the search for extra polarisations an important test of general relativity. Data from three observatories or more can be combined to construct a null stream, where the plus and cross signals destructively interfere, leaving behind noise and/or extra polarisations. We develop a Gaussian process as a model-agnostic method to search for extra polarisations in the the third gravitational-wave transient catalogue.

Darren Croton
Cosmic dust as a dark matter discriminator
We use hydro zoom-in simulations of Milky Way-type haloes to explore dust as an observational discriminator between cold and warm dark matter. CDM, having more substructure, requires a higher supernova efficiency than WDM to achieve the same satellite galaxy number. These different supernova efficiencies create different dust populations around their host galaxies. I’ll show our initial results, focusing on both the overall dust produced and its distribution, for each cosmology. These differences may serve as an alternate galaxy-scale test in the long-running cold versus warm dark matter debate.

Hillary Davis
HI Terminal Velocities in hydrodynamic N-body "surrogate" models of the Milky Way
The development of an N-body/hydrodynamic “surrogate'' model of the Milky Way (MW) - a model that closely resembles the MW after many Gyrs of evolution - would be extremely beneficial for Galactic Archaeology. We examined two new MW “surrogate” models, built with the Nexus framework. These new models include gas and hence are more advanced compared to the previous Nexus MW surrogate model. The most sophisticated simulation allows gas to evolve thermodynamically, and includes star formation, metal production, and stellar feedback. In this talk, I will discuss results obtained from these simulations with a focus on the so-called “HI terminal velocity curve'' - a heliocentric measurement of the maximum Vlos as a function of Galactic longitude (l). It is a powerful approach to indirectly estimating the gas dynamics, because it does not require knowledge about the distance to individual gas clouds, which is difficult to estimate. A comparison of the terminal velocities and recovered rotation curve values in the simulations against observations suggests that the models are in need of further refinement. I close my presentation by discussing possible ways forward for future models.

Allan Ernest
Gravitational Quantum Mechanical Effects on Galaxy Halo Composition: Predicting Gas Phase Fractions and Dark Matter Content
Gravitational quantum mechanics (GQM) introduces a novel view of the dark matter phenomenon. The mathematics of GQM predicts that a particle’s electromagnetic scattering cross section can be significantly reduced within a galaxy halo’s gravitational potential well, with the reduction depending on the particle's gravitational eigenspectral composition. This effect has been demonstrated experimentally with neutrons in Earth's gravitational field. This environmentally-induced reduction in interaction cross section could eliminate the need for beyond-Standard Model particles to explain dark matter. GQM associates "quasi-temperatures" with halos, corresponding to the average de Broglie wavelengths of the weighted eigenspectral components comprising the particle-halo wavefunction. These predicted quasi-temperatures align well with observed temperatures across all scales and predict the relative phase fractions (HI, HII and molecular H) of the halo gas. The theory also explains why some galaxy halos appear to have no gas, or be gas dominant with virtually no dark matter, while others appear to be extremely dark matter dominated. The theory further predicts that some dwarf galaxy halos should have quasi-temperatures below the HI formation threshold, making molecular hydrogen their dominant component. Traditional detection methods using molecular hydrogen proxies like CO become unreliable due to how GQM affects halo particle interactions. This suggests that the apparently high dark matter content in these dwarf galaxies may actually be undetected H2. Alternative detection methods using internal rovibrational transitions and Lyman-Werner spectroscopic transition lines, which are not subject to gravitational phase space darkness, could test this hypothesis.

Evgeni Grishin
Triple systems on the edge of chaos
I'll describe the pivotal role of triple systems in shaping the formation, observed properties and stability of various systems, from planetary satellites to merging black holes. In particular, I'll also show recent results on the stability of retrograde exoplanets in eccentric binaries and the effects of tertiaries on close chemically homogeneous massive binary exolution.

Samuel Hansen
Constraining radio AGN energetics and environments with the semi-analytic model RAiSE
The energy released by powerful radio AGNs – termed kinetic-mode feedback – is an important process in the evolution of galaxies. A wealth of radio-frequency observations of these objects are being collected in large-sky surveys (e.g., ASKAP EMU, MWA GLEAM, MeerKAT MIGHTEE) encoding constraints on the energetics of AGN feedback – if only these observations can be interpreted. We present a publicly available package capable of extracting key attributes from observed radio AGN images and performing a parameter inversion to constrain their energetics. The Radio AGN in Semi-analytic Environments (RAiSE) code is used as a forward model to produce synthetic surface brightness images of radio AGN lobes, enabling a range of model parameters to be extracted from an observed source, including jet power, source age and properties of the large-scale cluster environment. We demonstrate the ability of this technique to constrain the shape of ambient density profile using only radio images, previously limited to a small number of clusters with extensive X-ray observations. This work uniquely takes advantage of RAiSE’s ability to simulate AGN lobes at different spatial resolutions to dramatically increase the speed of the MCMC-based parameter inversion. This modified MCMC algorithm will have applications in a range of disciplines enabling a step-change in the run time of parameter inversions in the right circumstances.

Ryosuke Hirai
Influence of companion stars on supernovae: the tale of SN2022jli
Massive stars that cause core-collapse supernova explosions are known to be primarily born in binary and multiple systems. The supernova event(s) is one of the most transformative epochs of the binary's life, radically altering the course of evolution then on. The importance of this phase of evolution has been long recognized, but little attention has been made to the possible interactions immediately following the supernova. In this talk, I will report results from our work on the immediate consequences of supernovae in binaries such as the interaction between the supernova ejecta and companion star and new-born neutron stars colliding with companions. As a result of ejecta-companion interaction, we found that the companion envelope can inflate for a few years to decades, significantly altering its appearance. As for neutron star-companion collisions, we found that the neutron star can sometimes penetrate the star multiple times, accreting part of the star upon each penetration. By combining the findings of these two studies, we predicted that the neutron star may penetrate the inflated part of the companion envelope multiple times, possibly making observable features. Such a case was finally observed last year, where the supernova SN2022jli displayed periodic undulations in its light curve (Moore et al. 2023, Chen et al. 2024). We also report on our detailed modelling of SN2022jli, which should provide us with more insight into how massive binaries evolve towards forming stripped-envelope supernova progenitors.

Fitz Hu
How do tidal disruption events shine in optical and radio?
Tidal disruption events happen when stars getting too close to supermassive black holes. Radiations in all of X-ray, optical, IR and radio bands are observed from TDEs, whereas we still lack a universal model to explain all the observations. In this talk, I present our self-consistent hydrodynamic simulations of TDEs from a 1 solar mass star with real stellar profile disrupted around a 10^6 solar mass SMBH. We post-processed the hydrodynamic simulations and found that both optical (from thermal emissions) and radio (from synchrotron emissions) emissions produced that are consistent with the observations. Our work paves the first step towards a universal model for TDEs.

Amanda Karakas
The effect of mass loss and binary evolution on low metallicity AGB star yields
Low and intermediate-mass stars are the most numerous evolved stars in galaxies, and are important chemical factories when on the asymptotic giant branch (AGB) phase. These stars are major sites of production for carbon, nitrogen, and elements heavier than iron. Stellar yields from AGB stars are highly uncertain, with different groups often predicting wildly different abundance patterns. The divergence is particularly bad for low-metallicity intermediate-mass stars over about 2 solar masses. A significant part of the problem is attributed to mass-loss, which is highly uncertain. Furthermore, most theoretical studies of AGB stars focus on single stellar evolution but most stars over about 1 solar mass have a binary companion. How does a binary affect the ejected stellar yields? This latter question is best answered by modelling populations of AGB stars covering a large range in mass, separation and metallicity. In this talk I briefly mention our efforts to quantify the impact of mass-loss and binary evolution on the stellar yields of low-metallicity AGB models.

Mark Krumholz
Displaced gamma-rays from Terzan 5 as a probe of cosmic ray transport
The globular cluster Terzan 5 is the brightest globular cluster at GeV energies, and the only one detected at TeV energies. Mysteriously, however, the TeV emission is displaced roughly 10 pc in projection from the position of the cluster. I show that this displacement can be understood as arising from transport of anisotropic cosmic rays, and that the displacement distance in turn allows us to make the first ever direct measurement of the rate of cosmic ray pitch angle scattering, and thereby to constrain the mechanism responsible for setting the cosmic ray diffusion rate. I demonstrate that the data are consistent with cosmic ray self-confinement via the streaming instability.

Ilya Mandel
Common envelope evolution, outcomes, and associated transients
We describe some of our group's recent work on common envelopes. Our goal is to understand the onset and outcomes of dynamically unstable mass transfer, including the properties of the binaries left behind and the outflows during the common envelope stage. We have also started thinking about light curves of common envelope events.

Jordan Moncrieff
Localising BBH mergers to AGN through spatial correlations
The detection of gravitational waves from binary black hole (BBH) mergers in the stellar mass gap suggest that some proportion of mergers occur inside dense astrophysical environments such as active galactic nuclei (AGN). Certain astrophysical models suggest that a significant fraction (maybe even all) occur in AGN. We assess the feasibility of localising BBH mergers to AGN by analysing the angular cross correlation between GW localisations and galaxy catalogs.

Jack Nibbs
The potential for circumbinary disc creation from weak common envelope interactions
The common envelope phase of binary stellar evolution is a crucial part of explaining many phenomena, from x-ray binaries, luminous red novae, and short period binaries. All classic post-common envelope binaries have very short orbital periods, a feature that is relatively well understood within the framework of the CE inspiral. On the other hand, a class of post-red and asymptotic giant branch systems (post-RGB and post-AGB) appear to have wider separations, but also small enough that a common envelope interaction must have taken place. These systems always have a large, low mass circumbinary disk. I present scenarios to form large, circumbinary disks that form either as fallback of material that remains bound to the binary after the a CE interaction, or that are created by a weaker, ‘glancing’, interaction. My research explores the regime that must exist between a classical common envelope with its extreme in-spiral and a `glancing’ common envelope with a reduced in-spiral, by using 3D hydrodynamic simulations of both discs and the common envelope phase itself, as a two-pronged approach, to probe this intermediate regime and explain post-RGB and AGB binaries and related objects such as barium stars, CEMP stars and other post-interaction objects.

Fiona Panther
More than the sum of their parts: Resolving the boundary between black holes and neutron stars with post-merger gravitational waves
Determining the maximum possible neutron star mass is an open problem in astrophysics, and remains so due to the uncertainties in how matter behaves at supranuclear densities. Neutron stars close to this maximum mass limit will form through the merger of binary neutron stars (BNS), which can be readily detected via their gravitational wave emission. We describe a Bayesian method to combine signals from many BNS mergers to search for kHz frequency gravitational waves emitted by BNS post-merger remnants, and formulate an optimal statistic for post-merger GW detection. From our analysis, we can leverage the power of hierarchical inference to determine the maximum neutron star mass through the population properties of the remnants that are left behind: a mixture of the most massive neutron stars, and the lowest mass astrophysical black holes.

Claudia Reyes
Acoustic modes in M67 cluster stars trace deepening convective envelopes
Acoustic oscillations in stars are sensitive to stellar interiors. Frequency differences between overtone modes –large separations– probe stellar density, while differences between low-degree modes –small separations– probe the sound speed gradient in the energy-generating core of main sequence Sun-like stars. At later phases of stellar evolution, characterised by inert cores, the small separations are believed to become proportional to the large separations. Here, we present clear evidence of a rapidly evolving convective zone as stars evolve from the subgiant phase into red giants. By measuring acoustic oscillations in 27 stars from the open cluster M67, we observe deviations of proportionality between small and large separations, which are caused by the influence of the bottom of the convective envelope. These deviations become apparent as the convective envelope penetrates deep into the star during subgiant and red giant evolution, eventually entering an ultra-deep regime that leads to the red giant branch luminosity bump. The tight sequence of the cluster stars, free of large spreads in ages and fundamental properties, is essential for revealing the connection between observables –small separations– and the chemical discontinuities occurring in deep stellar interiors. We use this sequence to show that combining large and small separations can improve estimations of mass and age well after the main sequence.

Amit Seta
Magnetic field scale in the interstellar medium of the Milky Way
Magnetic fields play a crucial role in the dynamics of the interstellar medium of spiral galaxies and are often divided into large-scale, regular and small-scale, random components. Estimating random magnetic field properties from observations, even for our own Milky Way, has long been a challenge. This talk addresses the challenge by utilising pulsars in the Milky Way. Using an extensive dataset of over 1300 pulsars from the Australia Telescope National Facility Pulsar Catalogue, we combine pulsar dispersion and rotation measures with theoretical models to estimate the correlation scale of random magnetic fields to be 20-30 pc. This study enhances our understanding of the magnetic field length scales, which would be useful for the interpretation of rotation measures from extragalactic radio sources and can also help us further understand the role of magnetic fields in the dynamics and evolution of galaxies.

Megha Sharma
Binary collisions of stars by hypermassive black holes
Most galaxies host supermassive black holes at their centers, some of which exceed 10^9 msun in mass. Around such black holes, individual stars would be swallowed without producing observable signatures. However, binary star collisions could still occur, potentially leading to detectable emissions. In this work, I present preliminary results of binary star collisions in the vicinity of these black holes, simulated using a smoothed particle hydrodynamics (SPH) code.

Truman Tapia
Formation of ultra-diffuse galaxies and their globular cluster systems through mergers
Ultra-diffuse galaxies (UDGs), characterized by their extended radii and faint surface brightness, have attracted significant attention over the past decade. Despite the discovery of thousands of UDGs, their origins remain unclear, highlighting the need for further observational and theoretical investigations. In this study, we present a model for the formation of a UDG and its globular clusters through the wet merger of dwarf galaxies. Using the AZURA code, we perform high-resolution N-body and hydrodynamical simulations of two mergers and one isolated gas-rich UDG, employing a stellar particle mass of 500 solar masses and a softening length of 1 pc. Our results demonstrate that mergers can produce UDGs with globular cluster candidates, whereas the isolated galaxy does not form star clusters. The properties of the globular cluster candidates show trends consistent with those observed in the Milky Way's globular cluster system. Furthermore, the system of star cluster candidates is predominantly monochromatic, mirroring observations of several UDGs.

Thomas Venville
A search for dark matter annihilation from the Sagittarius Dwarf and Stream
While Dwarf Spheroidal galaxies are amongst the most promising targets for indirect dark matter (DM) detection experiments, extensive past searches have not found convincing evidence for DM annihilation in these objects. However, in Crocker et al. (2022) a gamma-ray signal was detected from the core of the Sagittarius Dwarf Galaxy (Sgr) at 8.1 sigma statistical confidence. In subsequent works we assess whether this emission could be a DM signal (Venville et al. 2024), then undertake a comprehensive re-analysis of Fermi LAT gamma-ray data to search for significant gamma-ray emission in the Sagittarius Stream. We overcome the difficulty of modelling the tidally disrupted Sgr and Sagittarius Stream DM distributions by computing the expected J-factor distribution utilising a hydrodynamic simulation of the formation of the Sgr and the Sagittarius Stream. We find the predicted J-factor value for Sgr, J_Sgr = 1.48 × 10^10 M_⊙^2 kpc^-5 (6.46 × 10^16 GeV cm^-5), would require a DM annihilation cross section incompatible with existing constraints in order for DM annihilation to explain the observed gamma-ray emission. The analysis of the Sagittarius Stream also failed to detect any significant gamma-ray emission attributable to DM annihilation. The fitted Sagittarius Stream gamma-ray emission is either degenerate with background sources or not detected in a given energy bin. This suggests significantly better characterisation of background sources is required for future analyses.

Mark Walker
A simple framework for understanding the R Coronae Borealils stars
R Coronae Borealis stars are remarkable stars doing remarkable things: they are hydrogen-deficient, carbon-rich supergiants that exhibit deep declines - sometimes fading by orders of magnitude as sprays of dust block the light. I'll describe a simple model for the dust extinction events, and describe how that model also accounts for the nature of the eclipsed star as a result of helium accretion onto a white dwarf.

Alex Wallace
Characterisation of Hidden Companions to Wobbling Stars
Since its first data release, the Gaia mission has provided a wealth of knowledge about the precise positions and motions of nearby stars. From this, we can measure parallax and proper motion to high degrees of accuracy. However, if a star is orbited by an unseen companion, the companion’s gravitational pull causes the position measured by Gaia to be slightly distorted. This causes a discrepancy between the measured position and the expected position of a single star which is quantified by the renormalised unit weight error (RUWE). In this talk, I present a method of identifying and characterising stellar companions based on a star’s RUWE value and other data, with a focus on exoplanets. I also identify how the next data release from Gaia will contain necessary information to significantly improve these results.

Sophie Young
Absorption processes in young radio galaxies
Astrophysical jets powered by accretion onto supermassive black holes at the centre of galaxies are among the most energetic phenomena in our Universe. Charged particles are accelerated along the jets to relativistic speeds, emitting synchrotron radiation observable at radio frequencies. Jets interact with the dense clumps of gas comprising their host galaxy and, on larger scales, the smoother and lower density circumgalactic medium. Interactions with the dense gas within the galaxy produce distinct observational signatures, allowing us to probe the physical properties of these environments. In particular, absorption features in both the continuum emission (such as free-free absorption) and spectral line profiles (such as HI absorption) form powerful tools for tracing the gas in the host galaxy and surrounding medium. In this talk, I will present the results of hydrodynamical simulations of astrophysical jets interacting with their surroundings on both galactic and circumgalactic scales. By comparing simulations with different host galaxy densities, jet powers, and large-scale environments, I investigate the impact of an inhomogeneous medium on the observed source morphology, radio spectra, and absorption profiles at different evolutionary stages. These simulations build upon the theoretical background underpinning jet-environment interactions across orders of magnitude in spatial scale, aiming to establish connections between observable quantities, jet evolutionary stages, and the intrinsic properties of both the jets and their surroundings. This will inform the interpretation of data from existing and future radio telescope surveys, providing insights into the feedback processes which influence galaxy evolution across cosmic time.