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Colloquia Series

For more information on colloquia at the Centre for Astrophysics and Supercomputing please contact Dr. Simon Stevenson and Dr. Stefan Osłowski ()

Swinburne Virtual Reality Theatre
AR Building, Room 104
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2018 Colloquia

Tuesday Oct 23, 10:30
Garry Foran (Swinburne)
Student Review: Garry Foran's pre-submission review
Garry's 30-month (pre-submission) review
Tuesday Aug 28, 10:30
Student Review: Vivek Gupta's 6 month review
Tuesday Aug 14, 10:30
James Esdaile ()
Student Review: Massive quiescent galaxies at z ~ 4--6
Thursday Jul 19, 10:30
Matt Pitkin (University of Glasgow)
Colloquium: TBC
Thursday Jun 21, 10:30
Joss Bland-Hawthorn (University of Sydney )
Colloquium: The Milky Way - evidence for Seyfert activity in the recent past
The Galaxy's supermassive black hole is a hundred times closer than any other massive singularity. It is surrounded by a highly unstable gas disk so why is the black hole so peaceful at the present time? This mystery has led to a flurry of models in order to explain why Sgr A* is radiating far below (1 part in 108) the Eddington accretion limit. But has this always been so? Evidence is gathering that Sgr A* has been far more active in the recent past, on timescales of thousands of years and longer. The bipolar wind discovered by MSX, the x-ray/gamma-ray bubbles discovered by ROSAT/Fermi, the WMAP haze, the positronium flash confirmed by INTEGRAL, and new UV spectroscopy from HST are suggestive of something truly spectacular in the recent past. We present new evidence that the Galactic Centre was a full blown "active galaxy" just a few million years ago. The echo of this incredible event can be seen today imprinted across the Galaxy. This leads us to a developing paradigm for Sgr A* activity over billions of years.
Thursday Jun 14, 10:30
Leo Alcorn (Texas A&M University, USA)
Colloquium: The Proto-cluster Environment at z~2: Kinematics, Metallicity, and Merging Groups
As near-infrared instrumentation comes into widespread use in extragalactic astronomy, we can observe the rest-frame properties of galaxies in over-dense or proto-cluster environments. These observations provide valuable information on the early affects of environmental density on galaxy evolution, and provide constraints on advanced cosmological simulations such as FIRE and Illustris-TNG. The ZFIRE survey has spectroscopically confirmed two such proto-clusters, at z=2.095 in COSMOS, and at z=1.65 in UDS, using the MOSFIRE instrument on Keck 1. We measure gas kinematics from the Hydrogen alpha emission line, and find no cluster-wide effects on kinematics, and a minor correlation between irregular morphology and angular momentum. In addition, we measure gas-phase metallicity on the group scale, attempting to measure indications of gas accretion or metal enrichment in the merging groups that define this proto-cluster. We determine if and when environmental density plays a role in early galaxy properties, which evolutionary processes are affected, and at what scale these processes act on members of over-dense regions at z~2
Tuesday Jun 12, 10:30
Daniel Berke ()
Student Review: Daniel Berke's confirmation of candidature review
Thursday Jun 7, 10:30
Alex Codoreanu (Swinburne)
Colloquium: Chemical fingerprints in quasar spectra: Intervening metal line absorbers from redshift 2 to 6
Absorption systems in the emission spectra of quasi-stellar objects (QSOs) provide an opportunity to study the distribution of metals in the Universe without the direct detection of the galaxies which have processed them. I study the spectra of four QSOs with emission redshifts 5.79=4.77, the comoving mass density (Ω) of MgII exceeds an expectation from the global metallicity of damped Lyα absorbers (DLAs) paired with the comoving mass density of HI.

I provide the first statistical study of SiIV beyond redshift 5 and I classify the CIV population by the presence of other ions and their velocity width. I find that all CIV systems with v>200km/s have associated low ionisation systems. I find that two such systems, separated by 550 physical kpc along the line of sight, are most likely tracing a multi-phase medium where hot and cold gas is mixing at the interface between the circumgalactic and intergalactic medium. I connect these observational discoveries to cosmological simulations and future investigations as well as the opportunity for future such observational studies.
Tuesday Jun 5, 10:30
Poojan Agrawal (CAS)
Student Review: Confirmation of Candidature
Thursday May 24, 15:00
Dr Alfred Tiley (Durham University)
Colloquium: Galaxy Kinematics from Integral Field Spectroscopy of ~1000 z~0.6-2 Star-forming Galaxies
I will present findings from our ongoing UK KMOS GTO programme that has measured the spatially-resolved gas properties for over 1000 emission-line galaxies at z~0.6–2. Combining this sample with ~800 galaxies at z~0 from the SAMI Galaxy Survey and ~400 more at intervening redshifts (z~0.4) observed with MUSE, we are able to probe the dynamics of star-forming galaxies over an interval of ~10 Gyr. This period encompasses ~70 percent of cosmic history and includes key epochs for galaxy growth and evolution. I will highlight recent results from our programme, including a measure of the redshift evolution of the Tully-Fisher relation since z~1 and an examination of the shapes of galaxy rotation curves between z~0.6-2. I will discuss how these analyses provide insights into the processes governing galaxy evolution in our Universe.
Tuesday May 22, 10:30
Student Review: Robert Dzudzar Review
Thursday May 17, 10:30
Rhea-Silvia Remus (University Observatory Munich)
Colloquium: Outer Stellar Halos of Galaxies from Field to Cluster Environment
The outer halos of galaxies are a fantastic laboratory to study
several important physical processes that shape the appearance of galaxies
in the universe. While dominated by the dark matter component, the outer
halos also harbor small galaxies orbiting around the main galaxy, and
often a faint stellar halo. Low surface brightness observations of these
stellar halos, as done for example using the Dragonfly telescope, often
reveal streams, shells, and several other indicators of merger events,
providing a unique insight into the formation pathways of individual
galaxies. Additionally, metallicity and stellar population gradients in
the smooth parts of the stellar halos provide information about the early
formation times of the galaxies. Such global outer stellar halos are
commonly observed in galaxy cluster environments, but only recently became
available for less massive galaxies. Using the hydrodynamical cosmological
simulation set Magneticum Pathfinder, as well as isolated merger
simulations, I will demonstrate how to decipher the information hidden in
the various components of these outer halos, and what we can learn from
Thursday May 10, 10:30
Sarah Leslie (Max Planck Institute for Astronomy)
Colloquium: Evolution of star formation and dust properties of galaxies over cosmic time
It is now well established that the star-formation activity of our Universe increased from the very early epochs, peaked around z=2, and then decreased by an order of magnitude until present age. However, the exact contribution of different galaxy populations to the total SFR budget is not yet well-defined. Further progress in this area requires both a better understanding (or calibration) of SFR tracers used as well as deep observations of such tracers. The international panchromatic Cosmic Evolution Survey (COSMOS), is the only single survey large enough to study the coupled evolution of the large-scale structure of the Universe, galaxies, star formation, and active galactic nuclei across cosmic time. The 2 sq deg area of sky covered by COSMOS has the most extensive set of multi-wavelength observations of any deep field sufficient to probe the high mass end of galaxy populations out to high redshift, spanning the entire electromagnetic spectrum from X-ray, UV, optical, infrared to the radio. In this talk I will cover two topics from my PhD work: 1) the evolution of galaxy opacity and dust distributions since z~1 and 2) the evolution of specific star formation since z~5 using radio continuum as a star formation rate tracer.
Tuesday May 8, 10:30
Cherie Day ()
Student Review: Cherie Day Confirmation of Candidature Review
"Localising the source of Fast Radio Bursts with UTMOST-2D", 6 month review talk.
Thursday May 3, 10:30
Nell Byler (ANU)
Colloquium: Self-consistent UV emission and absorption line diagnostics
UV diagnostics are critical for the study of high-redshift galaxies, given that commonly-used optical emission line diagnostics become observationally unavailable as they redshift out of wavelength regimes accessible from the ground. UV emission in galaxies is dominated by flux produced by young massive stars, along with line and continuum emission from ionized gas in the ISM. In this work, I assess the diagnostic potential of both absorption and emission features in the UV, using models that simultaneously and self-consistently consider stellar and nebular emission. I measure the metallicity sensitivity of established UV stellar absorption indices, and identify those that include a significant contribution from nebular emission. I identify combinations of strong emission lines that constrain metallicity and ionization parameter, and develop UV versions of the canonical “BPT” diagram. For nebular emission lines that overlap with known stellar wind features like C IV λλ1548,1551, I quantify the relative contribution from nebular and stellar emission to line ratios. I evaluate the diagnostics against observations of local galaxies and galaxies at high redshift and summarize the best diagnostic choices and the associated redshift range for low-, mid-, and high-resolution rest-UV spectroscopy in preparation for the launch of JWST.
Thursday Apr 26, 10:30
Angel Lopez-Sanchez (AAO)
Colloquium: Hi-KIDS: Linking gas and stars in nearby dwarf galaxies
In this talk I’ll present the "HI KOALA IFS Dwarf galaxy Survey" (Hi-KIDS). Hi-KIDS, which is part of ASTRO-3D, uses KOALA+AAOmega at the Anglo-Australian Telescope (AAT) to get good-quality IFS data of a sample of nearby dwarf and irregular galaxies for which we already have 21cm HI interferometric data, exploring a parameter space which is not studied by current IFS galaxy surveys. Hi-KIDS studies the global and local properties of the ionized gas (metallicity, SFR, kinematics) and the stellar component (star-formation history, kinematics) of nearby dwarf galaxies. It also compares the combined IFS+radio data with theoretical predictions of chemical evolution models to investigate the efficiency of the conversion of gas into stars. Hi-KIDS will provide a comprehensive picture of the physical processes ruling dwarf galaxies. In this talk I’ll present the motivations for conducting the Hi-KIDS survey, the status of the observations, and some preliminary results.
Thursday Apr 19, 10:30
Michelle Cluver (Swinburne)
Colloquium: Closing in on the HIdden universe
As the experiments looking to detect dark matter close in (coming from different directions on the Feynman Diagram), a small fraction of the baryon community is quietly anticipating a window on the universe (21cm neutral hydrogen) to de-fog a little. While theoretical simulators continue to grapple with the challenges of “mocking the universe”, observers can focus on refining (or even just beginning to understand) the prescriptive, previously sub-grid, physics and chemistry that made the universe great. I will talk about how star formation and stellar mass in galaxy groups can possibly make more sense if we can see the faint stuff (stars and gas) that everyone assumed was unimportant.
Tuesday Apr 17, 10:30
Matt Agnew ()
Student Review: Matt Agnew's 30 month reivew
Thursday Apr 12, 10:30
Dimitri Veras (University of Warwick, UK)
Colloquium: The growing field of post-main-sequence exoplanetary science
Connecting planetary systems at different stages of stellar evolution helps us understand their formation, evolution and fate, as well as provides us with crucial insights about their dynamics and chemistry. Post-main-sequence stars -- pulsars, white dwarfs and giant branch stars -- all host planetary systems, which often include remnant debris discs. Here I provide a review of our current knowledge of these systems. I show how this interdisciplinary field incorporates several facets of stellar physics and chemistry as well as solar system physics and chemistry, and detail simulation-based efforts to understand the big picture.
Tuesday Apr 10, 11:00
Debatri Chattopadhyay (Swinburne University of Technology)
Student Review: Debatri Chattopadhyay
Confirmation of Candidature
Wednesday Apr 4, 10:30
Richard McDermid & Francois Rigaut (Macquarie University)
Colloquium: MAVIS: A new MCAO-Assisted Visible Imager and Spectrograph for the Very Large Telescope
High-performing deformable secondary mirrors, and powerful, robust sodium lasers guide stars are becoming standard technology on the world's largest telescopes. This is enabling a new level of reliability, sky coverage, and precision for adaptive optics (AO), with multiple configuration options for different science applications. In particular, wide field, high-strehl AO performance has been demonstrated at infrared wavelengths through the use of Multi-Conjugate Adaptive Optics (MCAO). The high actuator density possible with deformable secondary mirrors is also enabling diffraction-limited performance at optical wavelengths, as demonstrated by recent observations at various 8m-class telescopes. MAVIS proposes to combine these two developments, exploiting the full capabilities of the European Southern Observatory's 4-laser guide star Adaptive Optics Facility, providing near-diffraction limited spatial resolution of an 8m telescope across a relatively large field of view. This Australian-led instrument will provide HST-like (or better) resolution from the ground, but with the light-gathering power of the Very Large Telescope (VLT), making it a powerful complement to future facilities like the space-based JWST and the 30-40m class ground-based telescopes currently under construction. We will present an overview of the foreseen MAVIS technical and scientific capabilities, and describe ways in which you can get involved in developing the science case for this exciting new instrument.

MAVIS factsheet
Thursday Mar 29, 10:30
Vid Irsic (University of Washington, USA)
Colloquium: Small scale structure of the IGM: A Dark Matter Tale
The intergalactic medium (IGM) plays a unique role in constraining the (small scale) matter power spectrum, since the low-density, high redshift IGM filaments are particularly sensitive to the small scale properties of dark matter. The main observable manifestation of the IGM, the Lyman-alpha forest, has provided important constraints on the linear matter power spectrum, especially when combined with cosmic microwave background data. This includes, most notably, the tightest constraints on warm dark matter (WDM) and fuzzy dark matter (FDM) models, that I will present in this talk.
Tuesday Mar 27, 10:30
Pipit Triani ()
Student Review: Confirmation of Candidature
Thursday Mar 22, 10:30
Eva-Maria Mueller (University of Portsmouth)
Colloquium: Constraining Inflation with large scale structure
Primordial non-Gaussianity (PNG) is one of the most promising probes to distinguish between different models of inflation, a theory to describe an era of exponential expansion of the very early universe that was first introduced to solve problems within the Big Bang model. Inflation can solve the horizon problem as well as the flatness problem, and can also explain the origin of structure formation through the creation of initial fluctuations. Currently, the best constraints on PNG are provided by measurements of the cosmic microwave background (CMB) with the Planck satellite. Even though current constraints from large scale structure (LSS) data are weaker than the CMB results, future galaxy surveys have the potential to significantly improve upon these limits by constraining the scale dependent halo bias induced by PNG. To fully exploit the information from galaxy surveys, optimal analysis methods need to be developed and applied to the data. I will present an optimal technique to directly constrain local non-Gaussianity from galaxy clustering by applying redshift weights to the galaxies and present preliminary results from the extended Baryon acoustic Oscillation Spectroscopic Survey (eBOSS).
Tuesday Mar 20, 10:30
Sarah Hegarty ()
Student Review: Pre-Submission Review
Wednesday Mar 14, 10:30
George Djorgovski (Caltech)
Colloquium: Quasars in the Time Domain
Quasars play a key role in our understanding of the physical universe and its major constituents. Variability is one of their key observable characteristics, and it is present at all wavelengths and at all time scales probed so far. It reflects directly the physics of their fueling and beaming, and offers a spectrum-independent method for quasar discovery that bypasses many selection effects. The field is being transformed by the large synoptic sky surveys and the resulting archives of light curves, that offer unprecedented opportunities for the systematic studies of quasar variability. I will describe several such projects, based mainly on the CRTS survey archive, including: a novel characterization of the stochastic variability of quasars, a discovery of a population of quasars with a periodic variability interpreted as a signature of the long-predicted supermassive black hole binaries, the most efficient method to date for a selection of quasar candidates, the discovery of megaflares in their light curves, a search for outliers in the variability parameter space that revealed interesting phenomena, including a population of type-changing quasars, etc.
Tuesday Mar 13, 10:30
Renee Spiewak (Swinburne University of Technology)
Student Review: Renee Spiewak

Renee Spiewak 18 month review.

Searching for and timing millisecond pulsars.
Thursday Mar 8, 10:30
Mike Hudson (University of Waterloo, Canada)
Colloquium: Galaxies and Dark Matter Seen Through a Gravitational Lens
The evolution of galaxies is linked to the growth and accretion histories of their host dark matter haloes. Weak gravitational lensing allows us to measure the evolution of their dark matter haloes, as well as the larger cosmic web that these haloes inhabit. I will review recent results from weak gravitational lensing and other methods that allow us to probe the dark matter content of the Universe on the scale of galaxies and so provide new insight into the processes that shape the evolution of galaxies. I will also discuss our recent detection of dark matter in the filaments of the cosmic web between galaxies. I will conclude by highlighting prospects from upcoming ground-surveys, and satellite missions.
Tuesday Mar 6, 10:30
Ellert vd Velden ()
Student Review: Student Review: Ellert vd Velden - Confirmation of Canditature
Ellert vd Velden 6 month PhD Review / Confirmation of Canditature
Thursday Mar 1, 10:30
Rachael Livermore (University of Melbourne)
Colloquium: Harnessing the Power of Gravitational Lensing
The magnifying power of gravitational lensing allows us to study distant galaxies in unprecedented detail. At moderate redshifts (1 < z < 5) the spatial magnification allows us to examine the kinematics and morphologies of ‘normal’ star-forming galaxies, revealing the processes that lead to the clumpy star formation observed in this epoch. At the highest redshifts (6 < z < 10), the flux magnification from lensing allows us to directly observe dwarf galaxies in the first billion years of the Universe, probing the faint end of the luminosity function where the majority of the ionizing photons that contribute to reionization originate. I will also discuss prospects for JWST in studying the first galaxies and the epoch of reionization.
Tuesday Feb 27, 10:30
Aditya Parthasarthay (Swinburne University of Technology)
Student Review: Aditya Parthasarthay
Aditya 18 month review.
Thursday Feb 22, 10:30
Roland Bacon and Johan Richard (Centre de Recherche Astrophysique de Lyon, France)
Colloquium: Science prospects with MUSE at the VLT
The Multi-Unit Spectroscopic Explorer (MUSE) is an integral field spectrograph with unique capabilities on the Very Large Telescope. With its high sensitivity and by providing a complete view of the optical spectrum over 1 arcmin2 it has been a tremendous breakthrough in the way galactic and extragalactic observations are performed. We will present a few examples where MUSE's transformational science capabilities are demonstrated. The success of MUSE calls for new ideas for the next generation of VLT instruments, and we will present the concept of a blue-MUSE: a wider field of view, higher resolution, blue-optimised version of MUSE.

Slides: Keynote
Slides: PDF
Tuesday Feb 20, 10:30
Pol Gurri (Swinburne University of Technology)
Student Review: TBC
Confirmation of Candidature
Thursday Feb 15, 10:30
Themiya Nanayakkara (Leiden University, The Netherlands)
Colloquium: Hunting for the first stars I: Attempts to demystify He II with MUSE
In the quest for identifying pop-III stars, the most sought-after emission line is He II, however, stellar population models are unable to accurately predict the He II features while being consistent with other emission line diagnostics. To produce He II ionizing photons, stellar populations require sources of hard ionizing radiation with energies >= 54.4 eV and sources such as AGN, shocks, X-Ray binaries, stellar rotation and/or binary stellar evolution, and post-AGB stars have been suggested as possible contributors. To accurately identify relative contributions from these wide variety of sources, high signal-to-noise spectra with rest-frame UV/optical coverage and advanced stellar population/photoionization models are required.

The VLT/MUSE GTO program has obtained deep ~10-30h exposures of the Hubble legacy fields yielding rest-UV spectra of galaxies at z~2-6. In this talk I will present recent results of the MUSE program, where we compare the z=2-4 He II emitters with expectations from photoionization modelling to explore their stellar population and ISM conditions. I will compare our results with recent results from local samples of high-redshift "analogues" to show the different parameter spaces probed by local and high-redshift galaxies in the rest-UV. I will address the necessity to obtain high signal-to-noise spectra of individual galaxies to model rest UV emission and absorption systems along with auxiliary rest-NIR lines to constrain stellar population properties of galaxies at high-z, which will be aided by combined studies by MUSE and JWST in future.
Tuesday Feb 13, 10:30
Uros Mestric ()
Student Review: mid-candidature
Thursday Feb 8, 10:30
Emily Petroff (ASTRON, The Netherlands)
Colloquium: Detection and follow-up of fast radio bursts
Fast radio bursts (FRBs), bright millisecond duration radio transients, are quickly becoming a subject of intense interest in time-domain astronomy. FRBs have the exciting potential to be used as cosmological probes of both matter and fundamental parameters, but such studies require large populations. Advances in FRB detection using current and next-generation radio telescopes will enable the growth of the population in the next few years from 30 to hundreds. Real-time discovery and follow-up, and new studies of the FRB population will provide us with some of the greatest insights in the coming years. I will discuss many observational aspects of the FRB population, including polarisation, searches for multi-wavelength emission, localisation, and repeating FRBs. I will also discuss how our response to these events can inform next generation surveys and pave the way for the enormous number of FRB discoveries expected in the SKA era.