Progress report on the search for compact massive spheroids at z=0.

TBD

The on-going growth in the size (volume) and collection rate (velocity) of modern datasets poses many changes for traditional visualisation-based knowledge discovery processes. Indeed, in many instances, the vast majority of the data that is collected will never be viewed by a human. Instead, there is an expectation that automated discovery systems utilising artificial intelligence and machine learning methods will be responsible for most of the analysis. What, then, is the point of humans, particularly in fields where visual discovery has played a prominent role? In this talk, I will provide an overview of highlights of my previous work addressing the specific data visualisation needs of one important class of humans: astronomers. This serves as motivation for addressing the collaborative, tactical, time-critical decision-making challenges presented by the Deeper Wider Faster astronomy program, which aims to detect the fastest transient objects in the Universe. Lessons learnt from studying astronomers in their natural habitat has broader applicably to the development of “Cyber-Human Discovery Systems”, where we seek to find a balance between automated discovery and human-centred insight in order to maximise the potential for discovery.

TBA

TBA

As per the ΛCDM cosmological model, the halo of the Milky Way was built up by the merging of numerous progenitor galaxies, as these dwarf galaxies brought in their own stellar populations (in the form of stars and globular clusters). Over time, the dwarf galaxies were tidally stripped by the Galactic potential, eventually leading to the formation of “stellar streams”. Therefore, stellar streams provide direct evidence of the hierarchical formation of our Galaxy.

Surprisingly, most of the known dwarf galaxy streams are dynamically-young systems that were only recently merged into our Galaxy (<~3-6 Gyr ago). However, the hierarchical paradigm of galaxy formation suggests that several dwarf galaxies must have merged into the Milky Way at earlier times (>~8−10 Gyr ago). These dynamically-old streams are likely to be discovered in the inner <~10-20 kpc regions of the Galaxy, and they hold the key to unravel the early formation history of the Galactic Halo.

I will talk about the “LMS-1” stellar stream, that we detect by searching for wide streams in the ESA/Gaia EDR3 dataset using our own STREAMFINDER algorithm. We detect LMS-1 as a 60° long stream to the north of the Galactic bulge, at a distance of ~15 kpc from the Galactic center, together with additional components that suggest that the overall stream is completely wrapped around the inner Galaxy. Using spectroscopic measurements from LAMOST, SDSS and APOGEE, we infer that the stream is very metal poor (⟨[Fe/H]⟩=−2.1) with a significant metallicity dispersion (σ [Fe/H]=0.4), and it possesses a large radial velocity dispersion (σ_v = 20 ± 4 kms−1). These estimates together imply that LMS-1 is a dwarf galaxy stream. Both the orbit and metallicity of LMS-1 are remarkably similar to the globular clusters NGC~5053, NGC~5024 and another stellar stream “Indus”. Even Pal~5 cluster overlaps with LMS-1 in the dynamical energy-action (E,J) space. These findings make LMS-1 an important contributor to the stellar population of the inner Milky Way halo.

Comparative Planetology is a terminology initially used for comparing our Earth to other solar system bodies to understand their similarities and differences. With the discovery of thousands of extrasolar planets (among them many are potentially terrestrial), this terminology has been increasingly popularised (with extended meanings) in exoplanet science. In this talk, I will discuss why and how understanding the star-planet chemical connections is crucial to conduct quantitative comparative planetology towards understanding the interiors, surface and atmospheres of terrestrial-type exoplanets. For a preview of some aspects of the relevant work you may find this page useful https://quanz-group.ethz.ch/research/models-simulations/planetary-composition.html

Observations of the transient sky to detect cosmic explosions critically rely on orbiting telescopes to cover the large range of wavelengths where atmospheric absorption and/or emission precludes the use of ground facilities. Thanks to dramatic technology improvements (Space 4.0), powerful miniaturised space telescopes operating as distributed-aperture constellations are offering new capabilities for high energy studies of transients to complement ageing existing satellites (Neil Gehrels Swift Observatory, Fermi GBM, INTEGRAL). With funding from the Australian Space Agency, the University of Melbourne is building SpIRIT, Australia's first space telescope, to be launched in 2022. SpIRIT is a gamma and x-ray nanosatellite that will operate as part of an international network of nanosatellites (the European High Energy Rapid Modular Ensemble of Satellites) for localisation of Gamma Ray Bursts (GRBs) and Gravitational Wave counterparts. Operations of an efficient X-ray all-sky-monitor with good localisation capability will have a pivotal role in the next decade on multi-messenger astrophysics, contributing to breakthrough discoveries in areas such as micro-second temporal structure of GRBs, their inner engines and jet composition. SpIRIT also has a strong link with the Australian space industry, and it aims to demonstrate new capabilities for on-board artificial intelligence and electric propulsion. In this talk, I will present an overview of the project, its current design and status, future plans, and highlight opportunities for collaboration.

Time: May 25, 2021 02:00 PM Canberra, Melbourne, Sydney
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Fast Radio Bursts (FRB) are one of the most intriguing transient phenomena discovered in the recent years, and recently observed down to 100-MHz frequencies. I will present the first southern hemisphere all-sky real-time imaging and radio-transient monitoring system, implemented on two prototype stations of the low frequency (50 - 350 MHz) component of the Square Kilometre Array (SKA-Low), the Engineering Development Array 2 (EDA2) and Aperture Array Verification System 2 (AAVS2). For the last two years these prototypes have been regularly collecting data to verify their performance against the SKA-Low specifications and simulations, including making all-sky images every two seconds used for transient searches. The transient identification algorithm used 2-second difference images to find candidates and required their detection in the images from both stations. In approximately 360 hours of data using a single coarse channel (0.926 MHz bandwidth), we identified a few episodes of extremely bright pulses from the pulsar PSR B0950+08 and several transients from an unknown object, which is currently under investigation. We also determined preliminary upper limits on surface density of radio transients at a 2-second timescale. We plan to increase the bandwidth by at least 40 times (to about 40 MHz) and time resolution to 10 ms or better in order to improve the sensitivity by two orders of magnitude and start detecting hundreds of FRBs per year. This upgrade will transform the stations into low-frequency FRB survey machines looking for FRBs and signals from extraterrestrial intelligence in high-resolution all-sky images, which will pave the way to similar searches with hundreds of SKA-Low station

One of the biggest questions in cosmology right now is whether the disagreement in the values of the Hubble constant inferred from various probes is due to new fundamental physics or simply due to systematic errors in our measurements. The main disagreement is between low redshift standard candles like supernovae, and high redshift probes like the cosmic microwave background, with baryon acoustic oscillations, lensing, gravitational waves all also chipping in to the mix. Enormous amounts of effort have gone into determining whether the magnitudes of standard candles and distances to standard rules are correct and unbiased, but much less work has gone into determining whether the redshifts are unbiased. This talk will review the current status of the H0 tension, and look into the oft neglected redshift axis as a possible cause, while simultaneously pointing out a couple of common misconceptions about redshifts and velocities in the expanding universe.

DTR review

https://swinburne.zoom.us/j/81967275098

Stellar feedback influences the structure and evolution of galaxies both near and far. Especially when it comes to massive stars, these objects are known to have a huge effect on their surroundings: they change the chemical composition of the gas around them via the stellar winds they eject, they explode as various energetic explosions like supernovae and gamma-ray bursts, and they leave remnants such as neutron stars and black holes, contributing to the dynamical evolution of the star-cluster or galaxy in question. What is more, these compact objects may merge and emit gravitational-wave signals for us to detect and follow up.

In this talk, I summarize what is currently known about massive stars – and in particular massive stars of metal-poor composition. These are the objects that were supposedly born in the first few generations of galaxies at cosmic ages, as well as those that may be present in local, low-metallicity dwarf galaxies, hidden in star-forming regions. Some of these stars can be directly associated with gravitational-wave emitting compact object mergers, at least from a theoretical point of view.

The field of metal-poor massive stars is actively and quickly developing these days. I will argue therefore that, while there has been many developments in recent years, one should expect new ones coming up, as more and more people turn their attention to these intriguing objects.

The Universe is an extremely dynamic place and for the most cataclysmic or fast events, the most interesting physics is occurring within the first seconds, minutes and days following its detection, motivating our need to be on-sky and observing a transient as soon as possible. I will describe the science driving my efforts to automate the Australia Telescope Compact Array (ATCA) and the Murchison Widefield Array (MWA). My research focuses on the rapid follow-up of short-duration gamma-ray bursts (GRBs), a known subclass of gravitational wave events that are well localised by the Swift telescope. ATCA can be on-target within 3 mins post-burst to probe the reverse shock emission from short GRBs, allowing us to determine a template of the radio luminosities and temporal behaviour of the gravitational wave events that will be detected by aLIGO/Virgo. As prompt radio emission becomes delayed with decreasing frequency due to dispersion, any prompt signals associated with transients may not arrive for seconds up to several minutes at MWA frequencies (80-300 MHz). The MWA automatic triggering response time of <20s is therefore fast enough to probe for the prompt FRB-like signals predicted to be produced by merging neutron star binaries (i.e. short GRBs). Employing image dedispersion techniques to search for prompt, coherent signals from short GRBs, we have placed strong limits on different merger models and scenarios, which will allow us to ultimately constrain different neutron star equations-of-state. While the MWA can be very quickly triggered, even the addition of dispersion delay does not make it possible for it to be on-target in time to detect a signal associated with an aLIGO/Virgo gravitational wave Superevent, which are only observed in the nearby Universe. However, I will describe how a combination of negative latency gravitational wave alerts and an unusual MWA configuration may make it possible to be on-target quick enough to search for associated prompt signals from a neutron star merger. Finally, I will discuss a new exciting collaboration between Curtin and Swinburne astronomers to study the low frequency components of FRBs by using the MWA to trigger on FRBs detected with UTMOST-2D.

This will be primarily an ***in-person*** review in the VR Theatre. Please physically come along!

Detections of the neutral hydrogen 21cm line in absorption can provide a powerful tool in understanding the role that cold gas plays in the formation and evolution of galaxies. The First Large Absorption-line Survey for HI (FLASH) takes advantage of the wide bandwidth, frequency range and radio-quiet site of the Australian Square Kilometre Array Pathfinder (ASKAP) telescope to search for HI out to redshifts of z=1, a parameter space which has been poorly explored until now. In this talk I will present an overview of the science case for the FLASH survey and show some early results obtained from pilot survey observations carried out last year.

For the last half-century, relativistic outflows accompanying the final collapse of massive stars have predominantly been detected via high-energy emission, as long-duration gamma-ray bursts (GRBs). From wide-field optical and radio time-domain surveys, there have been hints of related phenomena at lower energies, such as X-ray flashes. With the Zwicky Transient Facility (ZTF) we are conducting a systematic exploration of the broader landscape of engine-driven explosions, of which traditional GRBs are just one manifestation. The emerging zoo includes afterglows at cosmological distances with no detected GRB, broad-lined Ic (Ic-BL) supernovae with luminous X-ray and radio emission, and fast-luminous transients powered by circumstellar interaction such as AT2018cow. Understanding the origin of these events and their relation to GRBs will require coordinated observations between high-cadence optical surveys, wide-field gamma-ray monitors, and millimeter and radio observatories. This will be possible in the next few years with the launch of the Space-based multi-band astronomical Variable Objects Monitor (SVOM), the enhanced cadence of ZTF Phase II, and sensitive millimeter-band facilities like the Atacama Large Millimeter Array (ALMA).

The detection of gravitational waves and electromagnetic radiation from a neutron star merger, GW170817, heralded the dawn of a new age of astronomy - the multi-messenger era. In this talk, I will discuss follow-up of two landmark gravitational wave events - GW170817 and GW190814. Radio monitoring of GW170817 enabled tight constraints to be placed on the geometry and energetics of the merger, while VLBI imaging helped improve the "standard siren" measurement of the Hubble constant. No counterpart to GW190814 has been detected, but we have carried out 8 follow-up observations with ASKAP, covering ~90% of the localisation region. We have used these observations to carry out the most sensitive widefield radio transient survey to-date, and I will also present preliminary results from this search. I will outline prospects for radio follow-up of future gravitational wave events including the vital contributions that radio observations can make to the broader multi-messenger effort, and quantitative estimates for the detectability of events with current and future facilities.

Time: Mar 16, 2021 10:30 AM Australia/Melbourne
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Meeting ID: 846 4465 1795

This is Matthew Miles's CoC presentation.

Our current understanding of galaxy evolution hinges on the assumption that the universe has Solar-scaled metallicity abundances, which is not applicable outside our Solar System. This prohibits progress in understanding how the distribution of the metals in stars are recycled into the interstellar gas of galaxies throughout cosmic time. In this talk, I will present the first set of massive stellar evolutionary models developed that are computed self-consistently in all the input parameters of the models. These models are based on physically realistic metal abundances in HII regions using the Galactic Concordance scaling system, which allows us, for the first time, for us to accurately compare stellar observations against models that are not constrained solely against a single star, the Sun. The evolutionary tracks for our Galactic Concordance abundance scaling provide a more physically motivated approach than simple uniform abundance scaling with metallicity for the analysis of HII regions and have considerable implications in determining nebular emission lines and metallicity. As the surface enhancement of elements in massive rotating stars have broad impact on the ionizing spectra of high-redshift, low-metallicity galaxies, such stellar models with realistic, variable metallicities need to be considered to accurately model and predict the properties of galaxies across cosmic time.

CoC

Supernovae are explosive endpoints of stellar evolution. The most common two categories are core-collapse supernovae and thermonuclear supernovae. In core-collapse supernovae, the kinetic energy of the explosion is provided by the gravitational energy released when the iron core of an evolved massive star collapses to either a neutron star or a black hole. Open questions include how stripped supernovae lose their envelopes and which core-collapse supernovae make black holes and which make neutron stars. In part I of my talk, I will present examples of how optical integral field observations of the remnants of certain core-collapse supernovae, such as 1E0102.2-7219 or Puppis A, provide us with puzzling new structures that need to be understood if we want to make progress on the nature of their supernova progenitors.
In thermonuclear supernovae, the energy source is explosive nuclear fusion in white dwarf stars of lighter elements like helium, carbon, and oxygen, to heavier elements like silicon or nickel and iron. What kind of white dwarfs explode and how they evolve to ignition are still largely open questions.
In part II of my talk, I will present the recently discovered optical coronal line emission of the reverse shocked ejecta in three young thermonuclear supernova remnants and discuss a new approach to how these optical emission lines can be modelled to infer key parameters of the original supernova, such as explosion energy and mass.

TBD

https://swinburne.zoom.us/j/82298144371?pwd=STd3OWE2YmU1RlVmRVZoT0Jld0tEZz09