DTR talk

We’re excited to finally be able to show the supernova cosmology results from the completed Dark Energy Survey. We observed for 6 years with a custom-built camera on the CTIO-4m telescope in Chile, and followed-up with spectra from the Anglo-Australian Telescope. This produced a brand new sample of ~1500 type Ia supernova, which approximately quintuples the cosmology-quality high-redshift (z > 0.5) supernovae in the literature. We find tight constraints on dark energy and dark matter and see tantalising hints that the equation of state of dark energy may change with time. This amazing data also allowed us to detect gravitational lensing magnification of the supernovae (which gives information on the shape of dark matter haloes) and make a beautifully precise measurement of time dilation due to the expansion of the Universe.

Started in 2021, the Dark Energy Spectroscopic Instrument is currently undertaking the largest extragalactic survey of the Universe ever attempted, with a goal to map out and understand the mysterious “Dark Energy” that is driving it's accelerated expansion. In April, we released our first ground-breaking results, with the surprising and tantalising hint that Dark Energy may be time-varying rather than the usually assumed “Cosmological Constant". In this talk, I will discuss how we used the Baryon Acoustic Oscillation (BAO) pattern, encoded in the positions of galaxies scattered across the Universe, to make this measurement. I’ll then focus on some of the other exciting ways in which we are using galaxy survey data to expand our view of the Cosmos: by further modelling the full distribution (beyond the BAO) of galaxy positions and motions with Year 1 DESI data; and by augmenting these northern hemisphere efforts with the 4HS survey. Combined, these observations will lead to the first ~complete census of structures in the local Universe, hopefully completing a map more than 100 years in the making.

MCR review for Lydia Haacke. Note room only available for 30mins.

The cold dark matter model has been extremely successful in explaining several fundamental properties of galaxy formation and evolution, as well as the large-scale structure of the Universe. However, it exhibits some discrepancies at galactic scales, which has sparked interest in alternative dark matter models.

The study of the low surface brightness universe has gained momentum over the last 20 years, thanks to its potential to provide insights into the physics of our Universe. This is the universe with the lowest density of stars, where dark matter reigns. Consequently, the structural properties of low surface brightness objects are determined by the nature of the dark matter, and can be used to understand this elusive component.

In this talk I will discuss how recent developments in ultra-deep imaging are accelerating our ability to understand the nature of dark matter.

Local extreme starburst galaxies, many located in dwarf low-metallicity galaxies, provide perfect laboratories to characterise the physical processes that drive galaxy assembly and evolution, as star-formation is driven under conditions similar to those of the primitive galaxies, many of them now under study thanks to the JWST. However, the physical processes ruling star-formation, gas cycle, chemical enrichment, and the properties of both the stars and the ISM occur on different scales, and hence detailed maps of both local (sub-kpc level) and global properties of galaxies are needed. At the same time, spectroscopic observations need to be deep enough for detecting not only the bright emission lines including the critical [O II] 3727, but key, faint emission lines such as [O III] 4363 or He II 4686. "ISM and HII regions in extreme starbursts" has been identified as the Key Science Case for BlueMUSE Working Group 2: Nearby Galaxies. In this talk, I will provide an overview of the topic and how BlueMUSE can indeed dramatically advance our knowledge and understanding of starbursts, ISM, IGM, and HII regions in nearby galaxies. For this, I will also present some preliminary results of the "HI KOALA IFS Dwarf galaxy Survey" (Hi-KIDS), that uses KOALA+AAOmega at the Anglo-Australian Telescope (AAT) to get good-quality IFS data of a sample of ~100 nearby dwarf and irregular galaxies for which we already have 21cm HI interferometric data.

I will present results on the relationship between galaxies and their dark matter halos for massive galaxies and for dwarf galaxies. First, I will present results from Huang et al 2022 that use data from the Hyper Suprime Cam Survey (HSC) and gravitational lensing to show that the light from central galaxies is a much better tracer of halo mass than previously recognized. I will present four key results. First, custom measurements of outer light outperform “Cmodel” magnitudes as tracers of halo mass. Second, galaxy outer light correlates better with halo mass than galaxy inner light. Third, the outer light measured from 50 to 150 kpc has scatter comparable to richness based halo finders. Fourth, the shape of the lensing profile suggests that clusters selected according to galaxy outer light may have reduced selection effects compared to richness based methods. Finally, I will conclude with a discussion on how these results might be used to improve optical cluster finding algorithms. In the second half of this talk, I will present the Merian survey (https://merian.sites.ucsc.edu), a 60 night program on the Blanco telescope in Chile to probe the nature of dark matter in dwarf galaxies.

Spiral galaxies host the majority of star formation, yet the origins of the spiral features and their effects on gas and stars remain debated. A powerful way to probe these mysteries is by comparing the interstellar medium and stellar age properties on each side of spiral arms.

In this talk, I’ll share insights from IFU data on two spiral galaxies at z ~ 0.3 (3–4 Gyr ago) observed with MUSE and nine nearby spiral galaxies. We find intriguing trends: higher star formation rate and lower gas-phase metallicity in the leading edges of three galaxies, supporting density wave theory. Interestingly, a merging system NGC 2442 shows the opposite trend. Some other galaxies show no azimuthal variation -- consistent with dynamic spiral theory or could be obscured by observational scatter.

Observations only provide a snapshot of a galaxy’s evolution. We extend this study using the Auriga simulation, tracing stellar age variations across spiral arms over the past 5 Gyr. Our results reveal that gas-rich interactions can erase these azimuthal variations.

Please join me as we explore how spiral arms are shaped in real Universe and simulations.

Some of the first radio continuum radio sources to be identified were powerful radio-loud active galactic nuclei in very massive elliptical galaxies such as M87. As radio surveys have improved over the past seven decades, an increasing fraction of massive elliptical galaxies have been found to host radio continuum sources. I will present recent work using the Australian Square Kilometre Array Pathfinder to search for radio continuum emission from local very massive galaxies without star formation. We find a very large fraction of very massive galaxies are radio continuum sources. However, the radio powers of these sources can vary by orders of magnitude (at fixed galaxy mass), and there are some tantalising correlations between radio power, morphology and host galaxy kinematics.

Online only DTR for Luisa Buzzo. Zoom details TBD.

Jim's DTR

The universe may be vast and complex, but that doesn’t mean it has to be out of reach. As both an astrophysicist and a science communicator, I’ve seen firsthand how the power of effective communication can bridge the gap between scientific research and the wider community. In this talk, I’ll share my journey from academia to social media, and how I’ve navigated different platforms to connect with diverse audiences - from students and teachers to curious minds from all walks of life. We’ll explore the challenges and rewards of communicating complex astronomical concepts in engaging, accessible ways, and discuss why outreach is essential for the future of science. Together, we’ll dive into how science communication not only enhances public understanding but can also open new doors for researchers, students, and institutions alike.

Observations of galaxies have revealed a puzzle of different
properties seen from redshifts of z=10 or higher to present-day, using
multi-wavebands and integral field spectroscopy to probe the stellar
light, the gas, but also infer the dark matter content of galaxies at
different epochs of time. However, as observations represent snapshots in
time, connecting the puzzle pieces in their evolution requires simulations
to bridge our understanding of galaxy formation at early and late times. I
will present the results of this endeavor using one of the largest sets of
fully hydrodynamical cosmological simulations, the Magneticum Pathfinder
simulation suite and its adjacent simulations, going from the earliest
formation of galaxies to their present-day counterparts, and I will show
how kinematics, metallicities, mass distributions and gas properties can,
in concert, help disentangle the multitude of galaxy evolution pathways
that exist in the Universe. I invite you to join me on this journey of
galaxy formation through cosmic time, and discover how simulations and
observations together shed light on how structures have formed in our
Universe.

Update on AAL activities

The current generation of telescopes are sharp enough to observe chemical inhomogeneities in the interstellar medium of galaxies on a range of spatial scales. In this talk, I present a selection of novel statistical techniques that can be used to model galaxy data, characterise the spatial chemical distribution of galaxies, and make meaningful comparisons to both analytical and simulated models. For well-resolved data (finer than ~200 pc per pixel), I introduce the geostatistical modelling framework that allows the multiscale metallicity structure of galaxies to be modelled and key physical parameters to be extracted. For data that is more coarsely resolved, I demonstrate the power of forward-modelling to help resolve issues and assumptions associated with linear modelling of a metallicity gradient. Finally, I discuss a way to infer the presence of metallicity variations in unresolved sources by combining absorption and emission-based spectroscopy in host galaxies of gamma-ray bursts. These results shed light on the evolution of the interstellar medium of galaxies throughout cosmic time, and hold great promise for use in the analysis of future data sets.

The Universe is an extremely dynamic place, with explosive transients resulting from the death of massive stars as supernovae and gamma-ray bursts (GRBs), to the accretion onto, or merger of the resulting remnants. While most transients are discovered at optical, X-ray and gamma-ray wavelengths, the detection of associated radio emission allows us to track the relativistic ejecta that is shocking the surrounding medium and probe the central engines driving the explosions. My research explores the potential link between GRBs, gravitational wave (GW) events and fast radio bursts (FRBs). However, it is only through rapid radio follow-up within seconds to minutes post-burst that we can explore this link. The Murchison Widefield Array (MWA) and the Australia Telescope Compact Array (ATCA) are now capable of automatically responding to transient alerts through the use of rapid-response observing systems that begin observing GRBs on rapid (seconds to hours) timescales. The MWA response time of <10s can probe for prompt FRB-like signals predicted to be produced by GRBs. We seek to ascertain whether merging neutron stars (short GRBs and gravitational wave events) or massive stellar collapse (long GRBs) could produce supramassive neutron star remnants, and be progenitors to some FRBs. I will present the unique observing strategy we are employing with the MWA during the O4 LIGO-Virgo-KAGRA observing run to search for these FRB-likes signals. I will also explain how MWA triggered follow-up of GRBs are further refining central engine models. Using the ATCA rapid-response mode, we have obtained the very earliest detections of radio emission from GRBs to date. These observations form part of my PanRadioGRB program aimed at studying the radio afterglow evolution of all Swift GRBs in the Southern Hemisphere. Recent results include the detection of an unexpected radio flare likely caused by interstellar scintillation, placing the earliest size constraint on a GRB blast wave. We have also obtained the earliest radio afterglow detections of two short GRBs that are indicative of reverse-shocked ejecta and late time energy injection.

Whilst star formation (SF) in the interstellar medium (ISM) and the physics that govern it are some of the most fundamental mechanisms needed to paint a nuanced understanding of galaxy evolution, attempts to construct closed-form analytic expressions that connect SF and physical variables that have been observed to influence it, such as the density and turbulence properties of surrounding gas, still exhibit substantial intrinsic scatter. In this work we leverage recent advancements in machine learning (ML) and use symbolic regression (SR) techniques to produce the first data-driven, ML-discovered analytic relations for SF using the publicly available FIRE-2 simulation suites, which have no explicit numerical sub-grid recipe for SF. We employ a genetic algorithm-based SR pipeline that assembles analytic functions to model a given dataset called PySR, training it to predict symbolic representations of a model for the star formation rate surface density averaged at both 10 mega-years (Myr) and 100 Myr based on extracted variables from FIRE-2 galaxies. The equations that PySR finds that at both averaged timescales, SF is described by the surface density of gas, the velocity dispersion of gas and the surface density of stars. Furthermore, we find that the equations found for the longer SFR timescale all converge to a scaling-relation-like equation, all of which also closely capture the intrinsic physical scatter of the data within the Kennicutt-Schmidt (KS) plane. This indicates when trained on longer SFR timescales, this method leads to less overfitting and thus more accurate, trustworthy results.

In the context of hierarchical galaxy assembly, both globular clusters and dwarf galaxies serve as indispensable probes of the formation of our Milky Way. The chemical composition of stars within these ancient structures plays a pivotal role in constraining their chemical enrichment history. Each possesses its own chemical peculiarities; for instance, dwarf galaxies contain stars with low [$alpha$/Fe] compared to Galactic halo objects of the same metallicity. Meanwhile, globular clusters house multiple stellar populations characterized by distinct groupings in light element abundances. To date, most studies have focused almost exclusively on elemental abundances; however, nucleosynthesis operates at the isotopic level. This talk will discuss how magnesium isotope ratios shed light on both the accreted dwarf galaxy component of our Milky Way and the light element-enhanced populations within globular clusters. This reveals contributions from supernovae and low-mass stars that cannot be discerned through element abundances alone.

Transient events provide information on the extreme physics of the Universe and are used to constrain the effect of Dark Energy. Current challenges include their discovery in large surveys, understanding their intrinsic properties, as well as their use for precision cosmology analyses. In this talk I will introduce the project I lead, Fink. Fink’s goal is to discover the most promising astrophysical transients in large surveys and has privileged access to the mega facility Rubin Observatory. I will present our latest research on extreme transients with Fink. I will also showcase tantalizing new evidence that Dark Energy may not be constant with time. I will present my work on supernovae and machine learning and explain how it contributed to the tightest cosmological constraints to date with the Dark Energy Survey. I will conclude by discussing how Rubin will enable us to shed light on the diversity of transients and, for the first time, to find out whether Dark Energy is a constant or evolving with time.

Pulsars are a type of rotating neutron star that possess some of the strongest magnetic fields in the Universe. They emit highly polarised radio waves from regions above their magnetic poles, where the smooth change in linear polarisation state can be used to infer their magnetic geometry. Yet many pulsars display unusual deviations from these expected changes in polarisation. It has been proposed that such behaviours may be related to propagation through the extreme magneto-ionic environments that surround neutron stars, something that has been largely unexplored. In this talk, I will describe several recent advancements in polarimetric modelling and their application to high sensitivity pulsar observations obtained using Murriyang, the 64-m Parkes radio telescope. This includes the discovery and characterisation of a rare propagation effect in the unstable magnetic field of a radio-loud magnetar, and on-going efforts to determine the origins of circular polarisation and orthogonal-mode jumps across the pulsar population.

The ASKAP First Large Absorption Survey in HI (FLASH) is a large-area search for neutral hydrogen (HI) in and around distant galaxies at redshift 0.4 < z < 1.0, a cosmic epoch where our knowledge of the HI content of galaxies remains patchy and incomplete.

FLASH has two main science goals: to probe the evolution of the neutral gas content of galaxies, and to investigate gas accretion and feedback processes in active galactic nuclei. Radio searches in the HI 21-cm line are unaffected by dust extinction, and FLASH provides one of the first genuine ‘HI-selected’ galaxy samples at intermediate redshift. I will give an update on the current status of the survey (which has so far covered around 3000 square degrees of the southern sky), present some new science results from papers recently submitted or in preparation, and discuss the optical properties of the HI host galaxies. I will also outline the prospects for the full (24,000 square degree) ASKAP FLASH survey which is due for completion in 2028.

This review is online only.

We study the SDSS-IV MaNGA database consisted of spatially resolved spectra of ~10,000 galaxies to understand the emission properties of the associated ionizing sources. With the help of the BPT diagrams’ classification scheme, we train Spender (Melchoir et al 2021) to distinguish between the different spectra based on the dominant ionizing mechanism with information from the spectra outside of the strong emission lines usually used for classification. We find that a large fraction of LINER-like emission spectra can be distinguished by stellar absorption features associated with an old, metal-rich stellar component. This consistent with previous work finding that LINER emission could be driven by a stellar population of old low-mass evolved stars.

Ashwathi Nair COC Review: Formation channels of heavy binary neutron stars

The first observations with the James Webb Space Telescope (JWST) have uncovered a surprising and substantial population of compact red objects at high redshift (z = 4-9), previously undetected in even the deepest Hubble data. Subsequent ultradeep spectroscopy from the UNCOVER program revealed that these objects, colloquially known as "little red dots," exhibit ubiquitous broad Balmer lines and likely host powerful active galactic nuclei (AGN). If so, we may have identified up to 99% of known AGN at z > 4. But these are not your garden-variety type 1 QSO; their properties are weird, with some estimated black hole masses comparable to the stellar masses of their host galaxies, while in other cases the spectra display clear Balmer breaks, indicative of massive evolved stellar populations. I will present what we know so far about our new intriguing little friends, and discuss implications for our picture of early galaxy and supermassive black hole evolution.

We are currently in the fourth observing run (O4) for LIGO-Virgo-KAGRA (LVK). So far, the number of gravitational-wave candidates has almost doubled compared to the total number of events reported from the first three observing runs combined. The properties we infer from these observations have broad implications for the physics and evolution of massive stars, supernova mechanisms, our understanding of different sub-populations of compact binary systems, chemical enrichment of heavy elements in the Universe, and more. Recently, the LVK announced the detection of an exceptional event from O4: it's time to meet GW230529. In this talk, I will present the properties of this compact binary and discuss the astrophysical implications of this event.

Understanding how chemical elements are distributed in time and space across the universe provides key observational markers for the first stars. I'll summarise my team's recent efforts in tracing elements in the early universe using ESO/VLT/X-shooter via the EXQR-30 survey of intervening metal absorbers towards 42 z~6 quasars. With the benefit of the long lever arm from z=1.9 to 6.4, high sensitivity, resolution and significant number statistics, we have made meaningful inroads. Metal ions trace both chemical enrichment and the ionization state of the Circumgalactic Medium (CGM). We find that the ionization of the CGM differs significantly over the short period of cosmic time from redshift 5.5 to 6. I'll show how a decline in the incidence of intervening CIV absorbers, coupled with a rise in CII and OI complements current evidence for a late reionization continuing to occur in metal-enriched and therefore biased regions of the Universe. A flat evolution in weak MgII is also found, despite a decline in cosmic metal content. Finally, in direct comparison with JWST, I will demonstrate why medium resolution ground-based spectroscopy is essential for a complete census of the high-z CGM.

In this presentation, we address the difficult problem inherent in SKA of deploying complex astronomical applications under development on efficient target architectures that have not yet been built. Resource allocation in such scenarios has a significant impact on multiple factors such as latency, memory, energy, and cost among others. Solutions such as rapid prototyping make it possible to reliably simulate and generate efficient code for this purpose. At INSA-IETR we are developing the PREESM rapid prototyping tool to automate and accelerate this process. The tool is based on numerous thesis and internship projects as well as numerous collaborations such as Rising Stars, which is the subject of my presentation. This presentation will give an overview of the project's progress in our team. We propose methods based on the SDF (Synchronous Dataflow) model and clustering techniques to facilitate the deployment of applications on complex architectures such as CPUs, GPUs, and FPGAs on one or more machines. By providing a quick and easy solution to this NP-hard problem, our methods significantly improve the efficiency of astronomical application deployment.

Akhil's CoC review talk.

The majority of the baryons in the universe are in diffuse gaseous form and the quest to understand how the gas transitions to star formation fuel in a galaxy continues. I will discuss several projects that use observations and simulations to further understand this process (letting the audience choose which they would like to hear about). 1. How can we associate the phases of gas observed with different methods? 2. Are the cold clouds within a dark matter halo growing or being destroyed? 3. What does the interface between the disk and halo look like in simulations?, 4. Do dwarf galaxies have a CGM and what happens to it as a satellite galaxy?, 5. Related to the previous question, what is the census of gaseous satellites around spiral galaxies in the local Universe compared to the Local Group?

The dynamical and hydrodynamical evolution of stars and stellar remnants is greatly affected by the dense galactic nuclei (GN) environment. We explore the complex interplay of several physical processes that shape the properties, rates and environments of nuclear transients and black hole (BH) mergers and gravitational-wave (GW) events: i) We show how stellar dynamics shape the rate and properties of stellar BH mergers, extreme mass ratio inspiral (EMRI) and tidal disruption events (TDE). ii) For active galactic nuclei (AGN), we study how the presence of an accretion disc modified the light curves of exploding supernovae and their relation to other nuclear transients. iii) We examine in detail the gravitational torques in AGN discs that drive BH's radial migration. We find that thermal torques greatly alter the existence and nature of migration traps in AGN discs, which are believed to be responsible for massive hierarchical GW mergers. We find that GW mergers predominantly occur in low-luminosity AGNs. Finally, We combine the AGN disc modelling with merger recoil kicks to further explore the parameters space and constrain the efficiency of BH mergers for different generations.

We are living in a golden age of extragalactic astronomy: observations over broad wavelength ranges, wide fields and unprecedented depth are allowing us to uncover important details on the formation and evolution of galaxies. Yet, key quantitative aspects on the properties of galaxies remain not well constrained. The most important such aspects are the stellar mass, the star formation efficiency (how much of the initial reservoir of gass is turned into stars), and the dark matter distribution of galaxies. Lack of precise knowledge on these quantities is limiting our progress in both galaxy evolution and cosmology.
Gravitational lensing is one of the most reliable tools to measure galaxy masses at cosmological distances, and therefore offers a solution to this problem. Ongoing and upcoming missions such as Euclid and the Chinese Space Station Telescope (CSST) will enable the discovery of tens of thousands of strong lenses, opening up the era of statistical strong lensing. I will discuss the opportunities that statistical strong lensing will bring for our understanding of galaxies, as well as the challenges associated with it.

The Universe started without the heavy elements that make the complexity of our surrounding world (e.g. carbon, oxygen). In this talk, I will showcase ground-breaking advances in the numerical modelling of how these chemical elements are produced in stars, how they are dispersed around galaxies by energetic events, and how they get ionized to power the emission and absorption lines we observe in the spectra of distant objects. Leveraging these new prediction capabilities will take us from interpreting the highest-redshift emission lines observable by JWST to the most local chemical abundances of Galactic stars, shedding a new light on how metal-poor stars enriched the Universe in the process.

When talking about interference sometimes the point gets a bit fuzzy. Do we lock onto the physics of waves? Or particles? Or somehow use both? My PhD has focused on developing appropriate language, activities and more to remove most of the challenging questions we face when talking about quantum science. I have developed a series of lessons for Year 9 students (aged 14-15) and their science teachers, that step them through the uncertainty in interference. Concepts covered include photons as packets of light energy, wave and particle models (including an improved description), probability, and momentum. The activities form a sequence of lessons from Year 3 to 10 as part of the Einstein-First program. Through tests and interviews I have found that the students understanding changed because of the program. Students became more certain in their understanding of the uncertainty of quantum science.

Observations of stellar nurseries, and massive stars and their fates have led to stellar evolution models of ever-increasing complexity. These models also predict the existence of stars with more than 100 solar masses, which may have no analogues in the local Universe, and exotic types of stellar explosions. One of those predicted, yet not securely discovered object classes, are pair-instability supernovae (PISNe). Confirming or refuting their existence and measuring their properties are critical for stellar evolution theory, supernova science and gravitational wave astronomy. In this talk, I will give an overview of the current search efforts for PISNe, discuss the properties of the most promising candidate and the challenges it imposes on theoretical models and how we can leverage that to find PISNe with the Vera Rubin Observatory Legacy Survey of Space and Time and upcoming space missions.

We have collected stellar spectra for more than 210 million stars in our galaxy. In this talk I will argue that there is good reason for that: stellar spectra are uniquely informative tracers of cosmic evolution. The age and composition of stars trace the formation of the universe across many orders of magnitude in both space and time. For example, in our local neighbourhood the most ancient stars can tell us about star formation at redshifts higher than what is possible with JWST, and the more common stars are explaining missing physics in stellar evolution, nucleosynthesis, and planet formation. I will describe our efforts to collect even more spectra through SDSS-V. I will include some stunning results from the new Local Volume Mapper instrument. And I'll explain some broadly applicable data analysis methods that we have developed to enable this stellar science.