A toy model of galaxy evolution inspired by stellar metallicity measurements from the SAMI survey

Wednesday December 2nd 2020 @12pm, Zoom Colloquium
Dr Sam Vaughan The University of Sydney

Email: sam.vaughan[at]sydney.edu.au


Nearby galaxies can be divided into two broad categories: those which have blue colours, disc-like morphologies and are forming stars; and those which are red, have spheroidal morphologies and have ceased their star formation. Explaining why this is the case is a key challenge of galaxy evolution theories, but a comprehensive theory of what causes galaxies to quench their star formation is still missing. I will discuss a toy model of quenching which successfully reproduces a number of important differences between quiescent and star-forming galaxies at redshift 0, including their different mass-metallicity relations and mass-size planes. This model was born out of my studies of stellar metallicities in the SAMI galaxy survey, and I will also give a brief summary of my metallicity measurements and some of the powerful statistical tools I’ve used in my analysis.

CMB Cosmology with BICEP/Keck and SPT-3G

Wednesday November 25th 2020 @12pm, Zoom Colloquium
Dr Neil Goeckner-Wald KIPAC

Email: ngoecknerwald[@]gmail.com


Precision measurements of the anisotropies in the Cosmic Microwave Background (CMB) have become one of the cornerstones of modern cosmology. One major objective of current CMB experiments is the discovery of a stochastic background of gravitational waves generically produced by theories of cosmic inflation. Such a signal could be detected as an excess of odd-parity polarization in the CMB at degree angular scales. The South Pole Observatory is a coordinated effort between the South Pole Telescope (SPT) and the BICEP/Keck collaborations that will use the synergies of the two experiments to search for this signal in the presence of galactic and gravitational lensing foregrounds with unprecedented sensitivity. In this talk I will discuss some recent and upcoming results from both projects focusing on the search for inflationary gravitational waves in the CMB.

Veloce – and what it takes to open new discovery phase space for exoplanets, without spending a bomb.

Wednesday November 18th 2020 @12pm, Zoom Colloquium
Prof Chris Tinney UNSW

Email: c.tinney[at]unsw.edu.au


Breakthrough discoveries in astronomy invariably come through one of two routes – applying established techniques to new classes of objects discovered from new classes of surveys, or pushing established techniques to new levels of precision to make available previously unexplored observational phase space. Examples of the former include the discovery of T and Y-class brown dwarfs from surveys like 2MASS or WISE, or higher and higher redshift QSOs from larger and larger surveys.

Opening new phase space through higher measurement precision has been particularly prominent lately – exoplanets being first discovered by increasing precise Doppler measurements, more exoplanets being discovered by increasing precise photometry from space, or gravitation waves being confirmed by increasingly precise strain meters.

The Veloce instrument on the AAT seeks to push the boundaries of increasingly precise Doppler velocity measurement at a fraction of the cost of competing instruments. I’ll describe what it takes to make your instrument more precise, at lower cost, than other leading brands.

The evolution (or not) of the star formation efficiency, dust content, and duty cycle of high-z galaxies

Wednesday November 11th 2020 @12pm, Zoom Colloquium
Dr Jordan Mirocha McGill University

Email: jordan.mirocha[at]mcgill.ca


A relatively simple model has emerged in recent years that can explain the bulk properties of high redshift galaxies: star formation is fueled by the inflow of pristine material from the intergalactic medium, and proceeds with an efficiency that depends strongly on the mass of a galaxy’s parent dark matter halo but not obviously on cosmic time. We generally interpret this mass dependence as a signature of stellar feedback despite the fact that stellar feedback models also predict time evolution in the star formation efficiency. In this talk, I’ll focus on this apparent tension, and show that to remain in agreement with observations, competing feedback scenarios require qualitatively different assumptions about the properties of dust and the duty cycle of star formation in galaxies. As a result, I’ll discuss the prospects for distinguishing models based on the ‘dustiness’ and ‘burstiness’ of galaxies found in upcoming galaxy surveys with JWST and ALMA, and potentially via constraints on reionization from future 21-cm experiments.

Can uncertainties in the evolution of the massive stars explain EM and GW observations?

Wednesday October 21st 2020 @12pm, Zoom Colloquium
Poojan Agrawal Swinburne University

Email: pagrawal[at]swin.edu.au


Recent observations of galaxies and star clusters have highlighted the need for systematic studies dedicated to exploring the impact of uncertain parameters of stellar evolution on the properties of stellar populations. While the use of fitting formulae to stellar tracks remains a popular choice for modelling stellar evolution in population synthesis codes, they are not adaptable to changes in the stellar tracks. In this talk, I will present results from an alternative approach, METISSE, which uses interpolation between sets of pre-computed stellar tracks to approximate evolution parameters for a population of stars. It can readily make use of stellar models computed with different stellar evolution codes and can compare their predictions for populations of stars. Using METISSE with the data from two different stellar evolution codes, I will show how different physical ingredients used in the evolution of massive stars, such as the treatment of their radiation dominated envelopes, can lead to differences in their evolutionary properties. These differences are important as they can help us account for observations of the stellar populations and the formation of gravitational wave progenitors.

Probing the nature of dark matter with galaxy-galaxy strong gravitational lensing

Wednesday October 14th 2020 @12pm, Zoom Colloquium
Dorota Bayer Swinburne University

Email: dbayer[at]swin.edu.au


While a direct detection of the dark-matter particle remains very challenging, the nature of dark matter can potentially be constrained indirectly — by comparing the properties of substructure in galactic haloes with predictions from the phenomenological dark-matter models, such as the cold, warm or hot dark matter. Whereas these models are practically indistinguishable with respect to the predicted characteristics of high-mass substructure, the critical difference lies in the abundance and statistical properties of low-mass galactic substructure. Galaxy-galaxy strong gravitational lensing provides a unique opportunity to search for gravitational signatures of such low-mass substructure in lens galaxies beyond the Local Group. In this talk, I will present a novel approach to observationally constrain the statistical nature of low-mass sub-galactic structure in the inner regions of massive elliptical lens galaxies, based on the power spectrum of surface-brightness anomalies measured in highly-magnified galaxy-scale Einstein rings and gravitational arcs. A future comparison of these results with the predictions from hydrodynamical simulations might either verify the CDM paradigm or require its substantial revision.

Real or not real? What cosmological simulations can (and cannot) tell us about the cold phase of the CGM

Wednesday September 30th 2020 @12pm, Zoom Colloquium
Dr Lilian Garratt-Smithson University of Western Australia

Email: lilian.garratt-smithson[at]uwa.edu.au


Simulations are now allowing us to probe the scales of the CGM (circumgalactic medium) around galaxies in order to look at the influence of realistic galaxy formation processes. However, it is apparent that the properties of the multi-phase CGM are not yet converged in simulations (e.g. Van de Voort et al., 2019; Hummels et al., 2019), hence their reliability to make predictions is still in question. It is also clear the CGM plays a key role in the evolution of a galaxy; it is a supply of gas for star formation and a key site for feedback-generated outflows, along with the recycling of baryons (for a recent review see Tumlinson et al., 2017).

During this talk I will discuss the results of my recent paper (Garratt-Smithson et al. 2020 – available on astro-ph) and in particular the significant mass of HI seen in the CGM of EAGLE galaxies between redshift 2 and 0. I will explore the physical conditions of this HI, and discuss whether or not we can constrain the fraction existing in the cold neutral medium. I will also discuss the physical processes we can constrain by studying the detailed properties of this CGM HI gas; in particular I link my results back to AGN and stellar feedback, along with how this is modelled in simulations. Finally, I will discuss my current projects, which aim to explore the CGM in greater detail using a mix of idealised and cosmological zoom simulations.

Precision weak lensing and the dispersion in the stellar-to-halo mass relation.

Wednesday September 16th 2020 @12pm, Zoom Colloquium
Pol Gurri Perez Swinburne University

Email: pgurriperez@swin.edu.au


Weak gravitational lensing provides an observational avenue to determine the relation between the halo mass and stellar mass of a galaxy. While we expect two galaxies with the same stellar mass to have different halos, at the moment, existing weak lensing studies are only sensitive to an average halo mass. In this talk, I will present an end-to-end methodology to measure the effects of weak lensing on individual galaxy-galaxy systems exploiting their kinematic information. I will present the results of analysing 21 weakly lensed systems and present ways to overcome weak lensing limitations and be sensitive to the dispersion in halo masses.

IGM Attenuation Bias for Lyman Continuum Detected Galaxies at z > 3.0

Wednesday September 9th 2020 @12pm, Zoom Colloquium
Dr Rob Bassett Swinburne University

Email: rbassett@swin.edu.au


Understanding the sources responsible for driving reionization has been a major goal in astrophysics for many years. One critical measurement required is the ionizing (or Lyman continuum, LyC) escape fraction from observed galaxy samples. A major difficulty arises from the level of transmission of LyC through the intergalactic medium (IGM), an unknown (but essential) quantity in the calculation of LyC escape from individual sources. The typical method is to assume an average transmission value based on consideration of HI column density distribution functions, but is this appropriate? In general, observational surveys at high redshift are strongly biased towards the brightest objects as these are the easiest to detect. Given the fact that LyC emission is remarkably faint, we should expect to only detect those galaxies with the highest emergent LyC flux. This, in turn, suggests that detections of LyC in surveys will be biased towards IGM sightlines with higher than average transmission of ionizing photons. In this talk I discuss the quantification of this IGM transmission bias for LyC detections and explore the implications when considering the recovered LyC escape values from current surveys. Careful consideration of such biases will be critical in understanding how LyC escape depends on galaxy properties, which ultimately colours our understanding of how reionization proceeds.

Probing neural networks for science: What is it they are learning?

Wednesday August 26th 2020 @12pm, Zoom Colloquium
Dr Colin Jacobs Swinburne University

Email: colinjacobs@swin.edu.au


Neural Networks are finding increasing use in many areas of astronomy, but often act as “black boxes”. Many techniques exist to probe in the internals of neural networks but not all are relevant to scientists. In this talk I discuss some of the techniques developed in computer vision to investigate what neural networks are learning, and discuss some of their benefits and problems when applied to astronomy. I introduce a simple technique to probe what neural networks have learned and apply it to networks trained to find strong gravitational lenses.

Heavy Puzzle Pieces: Nucleosynthesis Models of the Intermediate Neutron-capture Process

Wednesday July 22nd 2020 @12pm, Zoom Colloquium
Melanie Hampel Monash University

Email: melanie.hampel@monash.edu


The quest for the origin of the elements in the universe combines different fields of physics and astronomy, from the smallest scales of nuclear reactions to large scales of giant stars. To understand the chemical history of our universe the abundances of elements heavier than iron are observed in the photospheres of old stars. The vast majority of heavy elements are formed by the slow (s) and rapid (r) neutron-capture processes. However, some observations of heavy-element abundance patterns of old stars are incompatible with either of these processes or even a combination of both.

I will show that these puzzling heavy-element patterns can be explained as the result of a separate neutron-capture process operating at neutron densities intermediate to the s and r process: the i process. Comparing theoretical predictions of i-process nucleosynthesis with the observed abundance patterns gives us new insights into uncertain phases of stellar evolution and will ultimately help us understand the origin of the elements in our universe.

Observational consequences of binary neutron star merger remnants

Wednesday June 17th 2020 @12pm, Zoom Colloquium
Nikhil Sarin Monash University

Email: nikhil.sarin@monash.edu


The first neutron star merger observed with gravitational waves and in electromagnetic radiation confirmed that binary neutron star mergers are the progenitors of at least some short gamma-ray bursts. The multi-messenger observations have been used to a probe a lot of fundamental physics, however, despite the wealth of observations the fate of the remnant of GW170817 is still uncertain. I will give an overview of binary neutron star mergers focussing on the nature of the remnant from observations of short gamma-ray bursts and theoretical considerations. I will discuss the implications of these observations on the nuclear equation of state, neutron star dynamics and gamma-ray bursts.

Cosmological tests using galaxy-galaxy lensing and clustering amplitudes in KiDS-1000

Wednesday May 6th 2020 @12pm, Zoom Colloquium
Prof. Chris Blake Swinburne University

Email: cblake@swin.edu.au


The physics of gravity on cosmological scales affects both the rate of assembly of galaxy large-scale structure, and the gravitational lensing of background light through this cosmic web. By comparing the amplitude of these different observational signatures, we can construct tests that can distinguish General Relativity from its potential modifications. We use the latest weak gravitational lensing dataset from the Kilo-Degree Survey, KiDS-1000, in conjunction with overlapping galaxy redshift surveys, to perform the most accurate existing amplitude ratio test on projected scales up to 100 Mpc/h. The scale-independence and redshift-dependence of these measurements are consistent with the theoretical expectation of General Relativity in a Universe with matter density Omega_m = 0.27 +/- 0.04. We demonstrate that our results are robust against different analysis choices, including schemes for correcting the effects of source photometric redshift errors.

The imprint of their explosions: Using supernova remnants to understand stellar death

(postponed due to Covid-19 pandemic social distancing measures) , level 7 Conference Room, David Caro Building
Dr Katie Auchettl The University of Melbourne

Email: katie.auchettl@unimelb.edu.au


One of the most uncertain aspects related to our understanding of the end points of stellar evolution is the link between the progenitor star and the nature of the supernova explosion that the progenitor will undergo. Even though hundreds of supernovae are discovered each year by optical surveys, these sources are usually too distance to resolve the ejecta and immediate surrounding of the exploded star. However, due to their long lifetimes and close proximity, supernova remnants which are the long lived structures that results from the supernova explosion of either a white dwarf or a massive star, provide us with a unique opportunity to study supernova explosion and dynamics up close and in detail. In this talk, I will highlight some recent advances that have been made in the understanding of supernovae and their progenitors using wavelength studies of supernova remnants.

Full of Orions? dissecting extreme, dusty starbursts on (k)pc-scales

Wed 11th March 2020 @2:15 PM, level 7 Conference Room, David Caro Building
Dr Matus Rybak Leiden University

Email: mrybak@strw.leidenuniv.nl


Sub-millimeter galaxies (SMGs) play a key role in the early Universe and are an important laboratory for understanding the most extreme star formation. However, our understanding of SMGs — what drives their intense star-formation? what are the physical properties of their star-forming ISM? – requires high angular resolution, long unavailable in mm/FIR wavelengths.

The start of ALMA operations in 2011 was a quantum leap from barely resolved SMGs to kpc-scales studies, matching or even exceeding the resolution achieved for present-day galaxies. A further order-of-magnitude jump in resolution – down to ~100-parcsec scales – has been provided by strong gravitational lensing.

I will showcase recent results from resolved multi-tracer (FIR, CO, C+) studies of dust and gas in z>2 SMGs at (k)pc resolution. Combining the superb angular resolution and high-frequency capabilities of ALMA, gravitational lensing and radiative transfer modelling, our results provide an unprecedented view of the conditions in these extreme star factories down to 50-pc scales .

Morphological transformations in the local Universe: an observational and theoretical perspective

Wed 4th March 2020 @12:00 PM, level 7 Conference Room, David Caro Building
Dr Camila Correa University of Amsterdam

Email: camila.correa@uva.nl


In this talk I will summarise recent results of the dependence of the galaxy stellar-to-halo mass relation on galaxy morphology. We use data from the Sloan Digital Sky Survey DR7 with morphological classifications from Galaxy Zoo, and also compare with the EAGLE cosmological simulation, to draw a coherent physical picture of the different evolutionary paths of discs and ellipticals. I will also explore possible scenarios of galaxies undergoing morphological transformation and quenching. To finalise I will discuss the limitations of current simulations such as EAGLE, and introduce the ongoing simulation project of EAGLE-2.

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


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


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


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


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


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


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


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


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


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


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


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


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


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.

Number of posts found: 201