Tenure-track position

Apply – deadline Monday, 16 Oct 2017
The School of Physics at the University of Melbourne is seeking the appointment of an outstanding female academic to a continuing (tenure-track) position of Lecturer or Senior Lecturer in astrophysics. The successful applicant will also be awarded an ASTRO 3D Fellowship within the ARC Centre of Excellence for All Sky Astrophysics in 3-Dimensions (ASTRO 3D), which allows for full time research during the first six years of the appointment.

ASTRO 3D spans six (6) Australian universities, three (3) national infrastructure facilities, and seven (7) international partner institutions. ASTRO 3D combines Australia’s leading optical, infrared and radio telescope technologies with sophisticated theoretical simulations and ambitious new data intensive science techniques to build a comprehensive picture of the evolution of matter, the chemical elements, and ionizing radiation in the Universe from the Epoch of Reionization to the present day.

The position is open to female researchers in any area of ASTRO 3D science. The appointee is expected to attract postgraduate students, engage collaborative links, and secure competitive research funding. The lecturer will supervise research students at MSc and PhD levels. At the conclusion of their ASTRO 3D fellowship, they will also have a core commitment to teaching within the School’s undergraduate and MSc programs.

The University seeks to increase the representation of women in areas where they have been traditionally under-represented. Pursuant to a Special Measure under Section 12 (1) of the Equal Opportunity Act 2010 (Vic), The School will, therefore, only consider applications from suitably qualified female candidates for this position.



Population synthesis of massive stellar binaries and predictions for the formation of (binary) black holes

Wed 26th Feb 2020 @12:00 PM, level 7 Conference Room, David Caro Building
Coen Neijssel University of Birmingham

Email: cneijssel@star.sr.bham.ac.uk

Abstract

Population synthesis codes enable us to simulate large populations of massive stars to compare to different types of observations. In this talk I will focus on the predictions for black hole masses both in high mass X-ray binaries and gravitational wave mergers. I will give a brief overview of basic stellar evolution and the prediction of remnant masses in the context of rapid population synthesis codes. Binary evolution can significantly alter the evolution of stars through events such as mass transfer and supernovae. I show what we believe is the most common formation channel for the binary black mergers we detect with current gravitational wave detectors. I will try to highlight what the critical assumptions are and which newer observations might contest previous results of the population synthesis community


The origin and fate of the discs of spiral galaxies from numerical simulations

Wed 19th Feb 2020 @12:00 PM, level 7 Conference Room, David Caro Building
Prof. Sukyoung Yi Yonsei University

Email: yi@yonsei.ac.kr

Abstract

I will present new results on the formation and fate of discs of spiral galaxies from the New Horizon and Galactica simulations. The high-resolution simulations (>40pc) reveal the history of disc settling, build-up, and fading in great detail and provide hints to the origin of the thin and thick discs.


Metal flows in simulated galaxies

Wed 5th Feb 2020 @12:00 PM, level 7 Conference Room, David Caro Building
Dr Chiaki Kobayashi University of Hertfordshire

Email: c.kobayashi@herts.ac.uk

Abstract

Stars are fossils that retain the history of their host galaxies. At the end of their lives, some explode as supernovae, producing heavy elements that are distributed into the surrounding interstellar gas. New stars that are created from this gas contain the elements that were produced from the previous generations of stars. From the spatial distribution of elements, it is therefore possible to constrain the star formation and chemical enrichment histories of the galaxies. This approach, Galactic Archaeology, has been popularly used for our Milky Way Galaxy. It can also be applied to external galaxies thanks to the recent and future observations with integral field units (extra-galactic archaeology). My team has been running hydrodynamical simulations from cosmological initial conditions including detailed chemical enrichment. By comparing with observations, I will discuss the roles of metal flows, i.e., gas infall, outflow, radial flow, and stellar migration, in the evolution of Milky Way Galaxy and galaxies in general.


Dark Energy and Exoplanets

Wed 29th Jan 2020 @12:00 PM, level 7 Conference Room, David Caro Building
Dr James D Rhodes NASA Jet Propulsion Laboratory

Email: jason.d.rhodes@jpl.nasa.gov

Abstract

The top recommendation for a large space mission in the US 2010 Decadal Survey was the Wide Field Infrared Survey Telescope (WFIRST). Similarities in hardware requirements between proposed dark energy, exoplanet microlensing, and near infrared surveyor missions allowed for a single mission that would accomplish all three goals. The gift of an existing 2.4 meter telescope to NASA by another US government agency allowed for the addition of a coronagraph that will take images and spectra of nearby exoplanets; this instrument will be a technological stepping stone to imaging other Earths in the 2030s. I will give an overview of WFIRST’s proposed instrumentation, science goals, and implementation plan.


Pulsar glitches and superfluid vortex dynamics

Wed 18th Dec 2019 @2:15 PM, level 7 Conference Room, David Caro Building
George Howitt The University of Melbourne (Completion Seminar)

Email: g.howitt@student.unimelb.edu.au

Abstract

Neutron stars are famously steady rotators, but some occasionally undergo sudden changes in their spin frequency known as glitches. I will discuss the theoretical and observational considerations for the origin of glitches in the superfluid interior of neutron stars, and present the results of simulations which show how interacting superfluid vortices in a model of a neutron star can produce similar behaviour to glitches in pulsars.


Be X-ray binaries in the Small Magellanic Cloud: A hint of the accretion efficiency during mass transfer?

Wed 27th Nov 2019 @2:15 PM, level 7 Conference Room, David Caro Building
Dr Serena Vinciguerra Max Planck Institute for Gravitational Physics

Email: serena.vinciguerra@aei.mpg.de

Abstract

Be X-ray binaries (BeXBs) consist of rapidly rotating Be stars with neutron star companions accreting from the emission disk. We compare the observed population of BeXBs in the Small Magellanic Cloud to simulated populations of BeXB-like systems produced with the COMPAS population synthesis code. We focus on the apparently higher minimal mass of Be stars in BeXBs than in the Be population at large. Assuming that BeXBs experienced only dynamical stable mass transfer, their mass distribution suggests that the efficiency of accretion rarely drops below ~30%. We also investigate the observed orbital period distribution and number of observed systems, looking for further constraints on our mass transfer models. Finally, we argue if ultra stripped stars could lead to fast rotating neutron stars in BeXBs. We expect our findings to affect our previous predictions on the population of double compact mergers.


Modelling the power spectrum on the light cone & preparing for the 4MOST redshift survey

Wed 20th Nov 2019 @2:15 PM, level 7, David Caro Building
Dan Pryer

Email: d.pryer@sussex.ac.uk

Abstract

This talk is broken into two parts:
 – The power spectrum is a powerful tool for measuring the large scale structure of the universe, and contains a wealth of cosmological information. As upcoming ’stage IV’ cosmology redshift surveys will map out the distribution of galaxies with a higher precision, and in a much larger survey volume than previous projects, it is important to review how the power spectrum is modelled and estimated. After going through a very brief review of large scale structure cosmology and two point statistics, I will give an overview of my work on how to accurately model the power spectrum when such large volumes are considered. I will give a particular focus to unequal-time correlators, and what the effect of using “effective redshift” approximations can have on the power spectrum amplitude.
– In the second part of my talk I will give an overview of the upcoming 4MOST cosmology redshift survey, due to launch in 2022. I will then discuss the ongoing development of the power spectrum estimation pipeline that will be used to test the mock catalogues for the survey, and how these can help for forecasting and survey design.

The build-up of mass and angular momentum in galaxies across morphology and environment with SAMI

Wed 6th Nov 2019 @2:15 PM, level 6 Opat Seminar Room, David Caro Building
Dr Jesse van de Sande

Email: jesse.vandesande@sydney.edu.au

Abstract

Studying the build-up of mass and angular momentum in galaxies is fundamental to understanding the large variations in morphology and star formation that we see in present-day galaxies. Integral Field Spectroscopy has revolutionised our capability of measuring resolved stellar kinematic data and has changed our classic view of early-type and late-type galaxies as two distinctly seperate populations. In this talk I will highlight several key results from the SAMI Galaxy Survey, which provides two-dimensional stellar population, gas and stellar kinematic measurements for ~3000 galaxies. I will show how specific angular momentum and lambdaR (spin parameter proxy) gradually change as a function of morphology and environment, and compare these to predictions from cosmological simulations. Furthermore, I will present recent results that link the intrinsic shape of galaxies and their stellar populations to their rotational properties.


Star formation, feedback, turbulence, and transport: towards a unified model for the dynamics of disc galaxies

Wed 30th Oct 2019 @2:15 PM, level 7, David Caro Building
Prof Mark Krumholz

Email: mark.krumholz@anu.edu.au

Abstract

In this talk, I review attempts to build a self-consistent model for the dynamical state of the interstellar medium (ISM) in star-forming galactic discs. Ideally such a model would incorporate star formation, stellar feedback, gravitational instability, the maintenance of turbulence, and transport of gas through the ISM into a unified framework, simultaneously explaining the relation between gas content and star formation (the Kennicutt relation), the observed correlation between galaxies’ star formation rates and velocity dispersions, and a variety of other observations. I summarise the various ways that theorists have attempted to fit together physical ingredients to reach this goal, the differing physical pictures behind these models, and the strengths and weaknesses of each when it comes to reproducing the observations. I then show that it is possible to combine the best elements of these models into a single, unified picture that successfully reproduces most of the major observations. I suggest future observations and numerical experiments that can be used to test this unified model.


Kinematics of star-forming galaxies at cosmic noon

Wed 23rd Oct 2019 @2:15 PM, level 7, David Caro Building
Dr Marianne Girard

Email: mgirard@swin.edu.au

Abstract

In this talk, I will present results from the KMOS Lensing Survey (KLENS) and KMOS Lens-Amplified Spectroscopic Survey (KLASS) that are exploiting gravitational lensing to study low-mass star-forming galaxies at 0.6<z<3.5. These star-forming galaxies are particularly interesting since they are Milky Way progenitors at this epoch. I will discuss how the kinematic properties of these galaxies around the peak of the cosmic star formation rate density differ from massive galaxies which have been analysed so far. I will also show results from our recent ALMA observations of two strongly lensed z~1 main-sequence galaxies and from a nearby galaxy sample, called DYNAMO, showing similar physical properties to high-redshift main-sequence galaxies. These observations allow us to compare the molecular and ionised gas kinematics at high spatial resolution for the first time (few hundred parsec in our z~1 galaxies). I will explain how this help us to better understand what drives star formation and the turbulence in galaxies at this epoch.


Characterizing and Mitigating Radio Frequency Interference in Reionization Cosmology

Wed 9th Oct 2019 @2:15 PM, level 7, David Caro Building

Mike Wilensky

Email: mjw768@uw.edu

Abstract

Through radio interferometry, we use redshifted 21cm radiation from neutral Hydrogen as a probe into the universe’s ionization history. The relevant wavelengths for observation are concurrent with those allocated for common radio broadcasts such as FM radio and digital television. Consequently, these transmissions can interfere with radio observations, and are thus dubbed radio frequency interference (RFI). The ever-looming threat of radio frequency interference demands that radio telescopes be placed in extremely remote locations. Even still, extremely remote telescopes such as the Murchison Widefield Array observe interference at non-negligible levels. In this talk, we introduce a new RFI mitigation strategy, known as Sky-Subtracted Incoherent Noise Spectra (SSINS), which was designed to detect extremely faint RFI. We show that the increased RFI mitigation afforded by SSINS makes a noticeable difference in redshifted 21cm power spectrum estimations. Furthermore, through analytic calculations and simulations, we characterize the expected effect of RFI on 21cm power spectra. Ultimately we conclude that RFI poses a serious threat to reionization science, and that pristine site conditions will be essential to making a detection of Hydrogen reionization.

The Rise and Fall of the First Galaxies

Wed 2nd Oct 2019 @2:15 PM, level 7, David Caro Building
Prof Ivo Labbe

Email: ilabbe@swin.edu.au

Abstract

The formation of the first galaxies is one of the most exciting frontiers in studies of galaxy evolution. We can now find galaxies when the universe was only a few percent of its current age, trace their rapid growth with time, and observe massive galaxies quench star formation only a billion years later. Yet significant questions and challenges remain. When did the first galaxies form? What are the properties of their stellar populations and their role in reionizing the intergalactic medium? And how do early galaxies relate to those observed at later times? I will review recent results from deep observations with ground- and space-based telescopes, highlighting recent insights from the final mission of the Spitzer Space Telescope and the Atacama Large Millimeter Array. Informed by these, I will look ahead as we prepare for the launch of the forthcoming James Webb Space Telescope.


Magnetic activity of Weak-line T Tauri stars, and hunting for planets in terrible (and not-so-terrible) places

Wed 28th Aug 2019 @2:15 PM, level 7, David Caro Building
Dr Belinda Nicholson

Email: belinda.nicholson@usq.edu.aub

Abstract

In recent years Doppler Imaging and Zeeman Doppler Imaging has enabled characterisation of the spots and surface magnetic fields of weak-line T Tauri stars. These objects are nearing the main sequence and so have cleared their inner discs and stopped accreting, but are still contracting and have an evolving internal structure. Examining the large-scale surface brightness and magnetic field maps for a small sample of weak-line T Tauri stars, we find that stars with similar brightness maps can have different magnetic field topologies. The magnetic map results more generally suggest some differences in the large-scale dynamo fields of weak-line T Tauri stars compared with classical T Tauri stars and main sequence stars of a corresponding spectral type.

In addition to studying weak-line T Tauri star magnetic activity, Doppler Imaging allows us to hunt for orbiting close-in giant planets. Early results indicate that the occurrence rate of close-in giant planets is higher among weak-line T Tauri stars than in the main sequence population.

Additionally, I will touch on the work being done at USQ’s MINERVA Australis facility following up and measuring masses for planetary system discovered by NASA’s TESS mission.


Apollo 11 After 50 Years

Wed 21st Aug 2019 @12:00 PM, level 7, David Caro Building
Prof. John Lattanzio

Email:  john.lattanzio@monash.edu

Abstract

The final 12 minutes of the Apollo 11 moon landing were filled with problems and ample reasons to abort. I will explain what was happening and why, and thus unlock the tension of those last few minutes. While the world watched in awe of the achievement, only Mission Control and the astronauts realised how close they were to aborting…for more than one reason.


Double Neutron Star Formation: A Population Synthesis Approach

Wed 14th Aug 2019 @14:15 PM, level 7, David Caro Building
Alejandro Vigna Gomez

Email:  avigna@star.sr.bham.ac.uk

Abstract

Neutron stars have been associated with pulsars, X-ray binaries, Galactic double neutron stars, short gamma-ray bursts, gravitational waves and luminous red novae. In this talk, I will discuss the study of double neutron stars using the COMPAS population synthesis code. I will focus on the orbital properties of the Galactic double neutron star population. I will also discuss the mass transfer episodes leading to common-envelope events for this population, which have been associated to luminous red novae.


Shedding light on the Epoch of Reionization with the 21cm signal

Wed 7th Aug 2019 @14:15 PM, level 7, David Caro Building
Dr Anne Hutter

Email:  a.k.hutter@rug.nl

Abstract

The Epoch of Reionization represents an important epoch in the history
in the Universe, when the first stars and galaxies gradually ionize the
neutral hydrogen in the intergalactic medium (IGM). Understanding the
nature of the ionizing sources, the associated ionization of the IGM,
and its impact on subsequent structure formation and galaxy evolution by
means of radiative feedback effects, represent key outstanding questions
in current astrophysics.

In the past few years high-redshift galaxy observations and simulations
have significantly extended our knowledge on the nature of high-redshift
galaxies. However, essential properties such as the escape fraction of
ionizing photons from galaxies into the intergalactic medium and their
dependency on galactic properties remain essentially unknown, but
determine significantly the distribution and time evolution of the
ionized regions during reionization. Analysing this ionization topology
by means of the neutral hydrogen sensitive 21cm signal with radio
interferometers such as the Square Kilometre Array (SKA) offers a
complementary and unique opportunity to determine the nature of these
first galaxies and pin down the reionization history.

In this talk, I will discuss how synergising high-redshift galaxy
observations with 21cm signal detections can provide constraints on
reionization. Furthermore, I will show results from a self-consistent
semi-numerical model of galaxy evolution and reionization, and discuss
the potential of inferring galactic properties, as the escape fraction
of ionizing photons, with the 21cm signal by means of its bispectrum.


Cosmic reionisation and the first stars

Thurs 1st Aug 2019 @14:15 PM, level 7, David Caro Building
Adélie Gorce Imperial College London/Institut d’Astrophysique Spatiale

Email:  adelie.gorce16@imperial.ac.uk

Abstract

During the Epoch of Reionisation (EoR), the first galaxies and AGNs ionise the neutral atoms surrounding them. Although essential, this period in the history of the Universe is still poorly known. We wonder about the sources: if it is generally admitted that the first stars led the process, more exotic sources such as the bright radiation of quasars might be needed. But also about the chronology: when were the first stars born? How efficient were they to ionise the IGM, what were their properties? Finally, about the topology: were overdense regions ionised first or last?…

In this talk, I’ll give an overview of the different observational ways available to learn about cosmic reionisation, from astrophysics to cosmology, from galaxy and quasar spectra to the 21cm signal. I’ll present the assumptions usually made to model reionisation and how they can impact the interpretation of observations. Finally, I’ll spend some time on the prospects of observing the 21cm signal to learn about the EoR, and in particular, what we can learn from the non-Gaussianity of the signal.


What can Lyα emission from galaxies tell us about reionization?

Email:  charlotte.mason@cfa.harvard.edu

Abstract

The reionization of intergalactic hydrogen in the universe’s first billion years was likely driven by the first stars and galaxies. The timeline of reionization is currently uncertain but if it is accurately measured it can unveil properties of ‘first light’ sources. I will describe how we can use galaxies at our current observational frontiers to learn about reionization. In particular, Lyman alpha (Lyα) emission from galaxies can be used to probe the intergalactic medium (IGM) at high redshift, but requires modelling physics from pc to Gpc scales. I will describe a forward-modelling Bayesian approach which combines cosmological IGM simulations with empirical interstellar medium models to constrain reionization from observations of galaxies, focusing on Lyα emission at z>6. I will present new measurements which favour a late and relatively rapid reionization, and place these in the context of high redshift galaxy formation. I will discuss the challenges and future prospects in using Lyα emission as a cosmological tool.


Morphology of cosmological fields during the epoch of Reionization

Mon 22nd July, 2019 @3:15 PM, level 6, David Caro Building
Akanksha Kapahtia, Indian Institute of Astrophysics

Email:  akanksha.kapahtia@iiap.res.in

Abstract

Neutral hydrogen is the dominant component of the universe after recombination with high density regions harbouring the first luminous objects. The radiation from these first luminous objects changes the thermal and ionization state of the intergalactic medium leading to a major transition in the history of the universe called the Epoch of Reionization (EoR). The EoR is marked by the appearance of ionized regions around these collapsed objects which grow and merge until the entire universe is ionized. The growth and topology of these ionized regions depends upon the properties of these first luminous sources. One important observational probe of the EoR is the 21cm spin flip hyperfine transition of the neutral hydrogen. The brightness temperature of this transition encodes the ionization and heating history of the IGM. We introduce real space morphological descriptors, called Minkowski Tensors (MTs) and topological quantities Betti numbers, to probe the morphology of the 21cm brightness temperature field. The MTs provide shape and anisotropy information of the structures in the excursion set of the fields, while Betti numbers describe the topology in terms of the number of connected regions and holes. We obtain different regimes of morphological evolution of brightness temperature, as the universe evolves depending upon different astrophysical settings of the EoR. Therefore, we show that the ionization history of the IGM can be reconstructed using the morphological description of brightness temperature in real space and help us further probe the properties of the first luminous objects.


Interferometric Imaging with PURIFY: Real Observations + Wide-field Corrections

Thurs 4 July, 2019 @12:00 PM, level 6, David Caro Building
Luke Pratley, Mullard Space Science Laboratory, University College London

Email:  luke.pratley@gmail.com

Abstract

The standard methods in radio interferometry for reconstructing images, such as CLEAN and its variants, have served the community well over the last few decades and have survived largely because they are pragmatic. However, they produce reconstructed interferometric images that are limited in quality and scalability for big data. In this work, we demonstrate the use of computationally distributed state-of-the-art sparse image reconstruction algorithms which have been implemented in the PURIFY software package. We do this by applying PURIFY to real interferometric observations from the Very Large Array (VLA) and the Australia Telescope Compact Array (ATCA), where PURIFY out performs CLEAN in modelling structure shown by the residuals. Lastly, we use PURIFY in wide-field imaging at low frequencies, where the w-projection algorithm models wide-fields of view with the non-coplanar w-term.The required accuracy and computational cost of these corrections is one of the largest unsolved challenges facing next generation radio interferometers. We show that the same calculation can be performed with a radially symmetric w-projection kernel, where we use one dimensional adaptive quadrature to calculate the resulting Hankel transform, decreasing the computation required for kernel generation by several orders of magnitude, whilst preserving the accuracy. We demonstrate the potential of our radially symmetric w-projection kernel via sparse image reconstruction, using the software package PURIFY. We develop a distributed w-stacking and w-projection hybrid algorithm where we apply exact w-term corrections for each measurement from observations from the Murchison Widefield Array (MWA), showing that it allows full wide-field correction for real data sets.


Exploiting non-Gaussian information to better understand the first stars and galaxies

Wed 3 July, 2019 @2:15 PM, level 7, David Caro Building
Dr Catherine Watkinson, Imperial College London

Email:  c.watkinson11[at]imperial.ac.uk

Abstract

The SKA and HERA are expected to detect the 21cm line of neutral hydrogen from the high-z Universe with great precision. This should allow us to learn about early generations of stars and galaxies, as we observe the impact of their radiation through ionisations and heating of hydrogen in the intergalactic medium.

As theorists, the challenge we face is how to best interpret these observations. Much work has already been done to develop MCMC pipelines using fast semi-numerical simulations. The current pipeline 21cmMC only includes the power spectrum as a metric to compare how similar a given simulation is to the data. I will discuss the benefits of including statistics that are sensitive to non-Gaussianity in the data.

To facilitate this discussion, I will provide an intuitive explanation of the bispectrum, why it might be an interesting statistic for many datasets, and how it is easier to measure than is often thought. I will also touch on some work I have been doing on likelihood-free parameter estimation which allows the researcher to concentrate on forward modelling their problem, rather than working out the appropriate form for the likelihood.


Bayesian Model Selection with Future 21cm Observations of The Epoch of Reionisation

Wed 26th June, 2019 @14:15 PM, level 7, David Caro Building
Tom Binnie, Imperial College London, UK

Email: t.binnie16@imperial.ac.uk

Abstract

We apply Bayesian statistics to perform model selection on different reionisation scenarios via the Multinest algorithm. Initially, we recover the results shown by 21CMMC for the parameter estimation of 21cmFAST models. We proceed to test several toy models of the Epoch of Reionisation (EoR) defined in contrasting morphology and scale. We find that LOFAR observations are unlikely to allow model selection even with long integration times. HERA would require 61 dipoles to perform the same analysis in 1080 hours, and becomes comparable to the SKA with 217 dipoles. We find the SKA requires only 324 hours of observation to conclusively distinguish between our models. Once model selection is achievable, an analysis of observational priors is performed finding that neutral fraction checks at specific redshifts add little to no inference. We show the difficulties in model selection at the level of distinguishing fiducial parameters within a model or distinguishing galaxies with a constant versus power law mass-to-light ratio. Finally, we explore the use of the Savage-Dickey density ratio to show the redundancy of the parameter Rmfp within 21cmFAST.


Precision timing and scintillation of binary radio pulsars

Wed 12th June 2019 @14:15 PM, level 6, David Caro Building,
Dr. Daniel Reardon, Swinburne University,

Email: dreardon@swin.edu.au

Abstract

Radio pulsars are precise clocks that can be timed using a detailed model of the pulsar, its binary orbit, and the ionised interstellar medium along our line of sight. This timing model can be used to test theories of dense matter, gravity in the strong field, and a set of the most stable pulsars can even be used as a Galactic-scale gravitational wave detector. In this talk I will describe my work to improve the timing models of pulsars through precision pulsar timing and by modelling their scintillation. I will highlight recent results for the nearest and brightest millisecond pulsar PSR J0437-4715, which include precise new distance and mass measurements, and a relativistic binary PSR J1141-6545. Finally, I will describe how these techniques will be useful for next-generation instruments including the Parkes ultra-wideband receiver, and the impressive MeerKAT radio telescope in South Africa.


To Illuminate the Dark Ages

Wed 5th June, 2019 @14:15 PM, level 7, David Caro Building
Dr Yuxiang Qin, Scuola Normale Superiore, Pisa

Email:  yuxiang.qin@sns.it

Abstract

The measurement of the cosmic 21-cm signal with the SKA will transform our understanding of the epochs of reionization and cosmic dawn. The properties of the first stars and galaxies are encoded in the patterns of the signal. Interpreting these patterns requires accurate and efficient models. I will present an update of the 21cmFAST semi-numerical simulation, which separately accounts for star-formation inside the very first galaxies. This unseen and transient population of galaxies obtain their gas through molecular cooling from the intergalactic medium, and could have markedly different properties from the more massive galaxies observed with Hubble and eventually JWST. I demonstrate that if the recently-reported EDGES signal at z~17 is genuinely cosmological, these molecularly-cooled “mini-halo” galaxies must have played a dominant role during Cosmic Dawn.


The Evolution of Super-massive Black Holes from Broadband Radio Surveys

Wed 29 May, 2019 @14:15 PM, level 7, David Caro Building
Dr Nick Seymour, Curtin University

Email:  nick.seymour[at]curtin.edu.au

Abstract

Radio surveys are unique probes of accreting super-massive black holes. Curiously, powerful radio emission is associated with both high and low accretion rates. Broadband radio surveys covering many decades of frequency allow us to select specific radio-loud sources as well as to characterise their jet power. I will present work at both low and high redshift studying the evolution of super-massive black holes selected from radio surveys. From deep multi-wavelength observations of the GAMA 23 survey field, I will present a study of a giant radio galaxy associated with a cluster at z~0.2. Modelling of the radio emission and the high current accretion rate suggests that this source may have had a recent change in its accretion state. I shall also present work using broad-band radio surveys and unique follow-up to identify some of the earliest super-massive black holes in the Universe. The ultimate aim of this project is to study the impact of radio-loud sources within the Epoch of Reionisation.


ZFOURGE & MOSEL : Emergent Galaxies at z~3.5

Wed 15 May, 2019 @14:15 PM, level 7, David Caro Building
Dr Kim-Vy Tran, UNSW

Email:  kimvy.tran[at]gmail.com

Abstract

ZFOURGE and MOSEL are deep observational surveys that track how galaxies assemble over cosmic time. ZFOURGE identifies approximately 70,000 objects up to redshifts of z~7 using a custom set of near-infrared imaging filters that provide high precision photometric redshifts. MOSEL targets emergent galaxies from ZFOURGE for spectroscopic follow-up to track this rapidly evolving population. Here I highlight results that include building a library of composite Spectral Energy Distributions and using the SED fitting code Prospector to determine star formation histories for a range of galaxy populations.


What reionized the Universe?

Mon 13th May, 2019 @14:15 PM, level 6, David Caro Building
Dr Koki Kakiichi, University College London

Email: k.kakiichi@ucl.ac.uk

Abstract

Study of reionization is now experiencing a surge of new insights, but the long-standing problem ‘what reionized the universe’ still remains unsolved. Hubble observations have placed a now-commonly-held view that the intrinsically faint galaxies are responsible for driving the reionization process, but with a fundamental assumption of large escape fractions >10%. A further puzzle comes from the recent deep spectroscopy of luminous galaxies and the spatial opacity fluctuation of the intergalactic medium (IGM) at z>5.7, which suggests a possibly important role of luminous systems and active galactic nuclei/quasars (QSOs). In the theoretical front, simulating early galaxies and the reionization process and is extremely challenging, requiring the understanding of the physics over a huge dynamic range from the scale of molecular clouds to the intergalactic medium. To shed light on these issues, we introduce a new spectroscopic programme surveying 56 QSO fields and a power of direct 3D mapping of galaxies and the IGM via 21cm tomography, which will be enabled by JWST, ELT, and SKA.


Space situational awareness and general perturbations methods for orbit propagation

Wed 8th May 2019 @14:15 PM, level 7, David Caro Building
Dr Emma Kerr RMIT

Email:  emma.kerr[at]rmit.edu.au

Abstract

The problem posed by space debris has been internationally recognised and many different methods tackling both mitigation and remediation have been proposed. One fundamental challenge though is accurate tracking and position prediction of objects in orbit. Beyond improving technology, the only method for tackling this challenge is in improving orbit propagation method. Orbit propagation allows a user to predict where an object will be in the future given its current position. This research focusses on improving general perturbations methods for orbit propagation. General perturbations methods for orbit propagation are typically considered to be less accurate and/or less useful than their numerical counterparts. The major problem facing these methods in terms of accuracy is that it is very difficult to capture time dependant phenomena such as the solar activity cycle’s effect on atmospheric density in a general perturbation solution. To date very little research on this topic has been published, as computers became more powerful it became less important to study such methods. However, as space debris has become such a prevalent issue, threatening the safety of both current and future missions, it has once again become prudent to look at methods that can allow the propagation of a large catalogue of objects in as computationally inexpensive way as possible.


The Simba Simulation

Fri 3rd May, 2019 @15:15 PM, level 7, David Caro Building
Professor Romeel Davé, University of Edinburgh

Email:  rad@roe.ac.uk

Abstract

The growth of black holes and their role in quenching massive galaxies is a key unsolved problem in galaxy formation. I present a new suite of cosmological hydrodynamic simulations called Simba, which builds on our successful Mufasa simulations to include a novel torque-limited black hole accretion model and AGN feedback using observationally-constrained bipolar kinetic jets. I will describe the physical motivations behind our new model, explain why they represent an improvement over other current black hole growth and feedback models, and demonstrate that they yield a galaxy population in very good agreement with numerous observations across cosmic time. These successes set the stage for exploring galaxy–black hole co-evolution towards better understanding the impact of AGN feedback on the baryon cycle along the mass hierarchy.


The future of gravitational-wave astronomy

Wed 1st May, 2019 @14:15 PM, level 7, David Caro Building
Dr Paul Lasky, Monash University

Email:  paul.lasky@monash.edu

Abstract

Gravitational-wave astronomy is now a reality. In the first two observing runs of Advanced LIGO and Virgo, there were ten detected black hole collisions, and one spectacular multimessenger detection of a binary neutron star merger. But what is next for this burgeoning field of gravitational-wave astronomy? I will discuss what we hope to learn from both black hole and binary neutron star collisions in the near future. This will include journeys into the exotic world of testing General Relativity in the ultra-strong field regime, and understanding bulk nuclear matter at supranuclear densities. I will also discuss the next generation of gravitational-wave instruments, and Australia’s potential to play a significant part in this global endeavour.


Number of posts found: 125