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.

Using Composite Spectral Energy Distributions to Characterize Galaxy Populations at 1 < z < 4

Thu 21 Mar, 2018 @12 PM, level 7
Ben Forrest, PhD student
Texas A&M University

Email: bforrest[at]physics.tamu.edu


Ben Forrest Ben Forrest, PhD student
Texas A&M University
Email: bforrest[at]physics.tamu.edu
With increasing sample sizes and multiwavelength photometric coverage of distant galaxies through surveys such as CANDELS, NMBS, and ZFOURGE, the available data at high redshift has grown significantly in the last decade. By de-redshifting and scaling photometry of many tens to hundreds of galaxies with similar spectral energy distributions, we can create low resolution spectra (R~50), quantifying features such as emission line equivalent widths with more precision than possible for a single galaxy without spectroscopy. In this talk I will detail the use of this method with ~7000 high signal to noise galaxies from the ZFOURGE survey. This allows us to identify and characterize populations of galaxies in the green valley, which show morphologies, dust content, and star formation rates between those of star-forming and quenched populations. I will also discuss those galaxies with extreme nebular emission in the young universe, which may be analogs to those which played a role in cosmic reionization.

Simulating GENESIS: The ASTRO 3D Theory programme

Thu 15 Mar, 2018 @12 PM, level 7
Dr. Pascal Elahi, Postdoctoral Fellow
The University of Western Australia

Email: pascal.elahi[at]uwa.edu.au


I will discuss the ASTRO 3D theoretical programme, which aims to follow galaxy formation and evolution across key epochs in cosmic time, from the EoR to the present-day, producing synthetic skies for ongoing and upcoming surveys. I will present current and near future simulations, how they compare to state-of-the-art work done else where, I will also discuss how we will tackle the variety of large scientific questions in ASTRO 3D’s other programmes. I will end with a taster of several specific scientific questions we seek to answer in the near term.

The fast radio bursts population as observed by the Australian Square Kilometre Array Pathfinder

Wed 28 Feb, 2018 @12 PM, level 7
Dr. Ryan Shannon, Postdoctoral Fellow
Swinburne University

Email: Ryan.Shannon[at]csiro.au


Fast radio bursts (FRBs) remain one of the most exciting and confounding classes of astronomical transients. There is mounting evidence that these bright, dispersed pulses of radio emission originate at cosmological (gigaparsec) distances. Not only do the energetics of the events point to a new radiative process, but the pulses are imprinted with propagation through the ionised intergalactic medium and cosmic web, making them invaluable probes of media invisible to most other types of observations. Despite considerable effort to detect additional bursts, the yields have been low because of relatively narrow fields of view of most searches. Here I will present the discovery of 20 FRBs from a wide-area survey conducted with the Australia Square Kilometre Array Pathfinder (ASKAP), nearly doubling the total number of known FRBs in only one year of surveying. The burst properties suggest a cosmologically evolving population with a wide luminosity function. I will then discuss future plans to develop interferometric fast transient capabilities with ASKAP, necessary to harness the full value of FRBs. To conclude, I will present the very recent discovery of two FRBs with the Parkes telescope, one of which is the highest signal-to-noise ratio burst seen to date.

Pulsar timing arrays

Wed 07 Mar, 2018 @12 PM, level 7
Dr. Stefan Oslowski, Laureate Fellowship Postdoctoral Research Fellow
Swinburne University

Email: stefanoslowski[at]swin.edu.au


The gravitational wave spectrum spans a large range of frequencies with various experiments covering different parts of the spectrum. At the low end of the spectrum, in the nanoHertz regime, we use so-called Pulsar Timing Arrays (PTAs) to try and detect gravitational waves. PTAs observe tens of millisecond pulsars spread throughout our Galaxy to form a galactic-scale detector. The primary signal PTAs attempt to detect are mergers of supermassive blackholes but we are also sensitive to more exotic sources like cosmic strings. During this talk I’ll provide you with an overview of the history of PTAs, current efforts and struggles, as well as the outlook into the bright future.

Science vs Cinema: Star Trek II – Wrath of Khan

Sun 8 Jul, 2018 @3.30 PM, NOVA cinema
Dr. Rachael Livermore, DECRA fellow
University of Melbourne

Email: rlivermore[at]unimelb.edu.au

Celebrate space and stars with a fun event for the whole family! Revisit classic sci-fi films on the big screen, followed by fascinating presentation and discussion on how space is depicted in cinema with Astrophysicist Dr Rachael Livermore (The University of Melbourne).

More details are here: Star Trek II – Wrath of Khan

Science vs Cinema: Apollo 13

Sun 17 Jun, 2018 @3.30 PM, NOVA cinema
Dr. Rachael Livermore, DECRA fellow
University of Melbourne

Email: rlivermore[at]unimelb.edu.au

Celebrate space and stars with a fun event for the whole family! Revisit classic sci-fi films on the big screen, followed by fascinating presentation and discussion on how space is depicted in cinema with Astrophysicist Dr Rachael Livermore (The University of Melbourne).

More details are here: Apollo 13

Science vs Cinema: Galaxy Quest

Sun 29 Apr, 2018 @3.30 PM, NOVA cinema
Dr. Rachael Livermore, DECRA fellow
University of Melbourne

Email: rlivermore[at]unimelb.edu.au

Celebrate space and stars with a fun event for the whole family! Revisit classic sci-fi films on the big screen, followed by fascinating presentation and discussion on how space is depicted in cinema with Astrophysicist Dr Rachael Livermore (The University of Melbourne).

More details are here: Galaxy Quest

Neutrino cosmology

Wed 28 Feb, 2018 @12 PM, level 7
Dr. Yvonne Wong, Senior Lecturer
University of New South Wales

Email: yvonne.y.wong[at]unsw.edu.au


Neutrinos are the most weakly interacting and one of the lightest particles in the standard model of particle physics. Ironically, while these characteristics make the neutrino elusive in the laboratory, they are precisely what makes neutrinos the most abundant known subatomic particle in the universe, averaging about 300 particles per cubic centimetre today. The sheer number of these particles makes them an important participant in many cosmological processes, from the primordial synthesis of light elements, to the formation of the cosmic microwave background anisotropies and the large-scale cosmic structures. In this talk I will review the role played by neutrinos in these processes.

Using Globular Cluster Stellar Populations to Understand Galaxy Formation

Wed 21 Feb, 2018 @12 PM, level 7
Dr. Christopher Usher, Postdoc
Liverpool John Moores University

Email: c.g.usher[at]ljmu.ac.uk


Globular clusters are important tools to help us understand how galaxies form and evolve. Globular cluster formation tells us about the conditions of extreme star formation while their survival from high redshift tell us about the processes of galaxy assembly. Being much brighter than red giant stars, globular clusters allow the stellar populations of galaxies to be studied at much greater distances. Thus a wider range of galaxy masses, environments and morphologies to be studied than can be with resolved stars. Using data from the WAGGS survey of massive star clusters in the Milky Way and its satellite galaxies and the SLUGGS survey of the globular cluster systems of massive early-type galaixes, I will talk about how we can measure the metallicities of globular clusters using the strength of the calcium triplet in integrated light. Using globular cluster metallicity distributions and the relationships between globular cluster colour and metallicity, I will present evidence that different galaxies with similar masses experienced different formation histories. I will compare these observations with the predictions of the E-MOSAICS cosmological simulations of the formation of globular cluster systems. I will also talk about how the E-MOSAICS simulations have allowed to us to understand how globular cluster colour distributions vary with globular cluster luminosity (the ‘blue tilt’).

Hunting for the first stars I: Attempts to demystify He II with MUSE

Wed 14 Feb, 2018 @12 PM, level 7
Dr. Themiya Nanayakkara, Postdoc
Leiden Observatory

Email: nanayakkara[at]strw.leidenuniv.nl


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.

Hierarchical Star Formation Across Space and Time with Star Clusters from LEGUS

Wed 7 Feb, 2018 @3PM, level 7
Kathryn Grasha, PhD student
University of Massachusetts

Email: kgrasha[at]astro.umass.edu


A key missing piece in a predictive theory of star formation is the link between scales of individual stars and star clusters up to the scales of entire galaxies. LEGUS, a HST Treasury program of 50 nearby galaxies imaged at UV and optical wavelengths, is now providing us the information to test the overall organization and spatial evolution of star formation. I will present my latest findings of using star clusters from LEGUS combined with millimeter observations to trace the hierarchy of the entire star-forming process to improve our understanding of the evolution of star formation, stellar populations, and the natal molecular gas in galaxies.

Stars and scintillations

Tue 23 Jan, 2018 @12PM, level 7
Mark Walker, Director
Manly Astrophysics, NSW

Email: Mark.Walker[at]manlyastrophysics.org


Our understanding of radio-wave propagation through interstellar space is evolving rapidly in response to new observational results. It now appears that radio-wave scattering is caused primarily by dense plasma organised in radial filaments around hot stars. The resulting picture of the circumstellar plasma environment looks much like the Helix Nebula, where ionised filaments arise as the cometary tails of tiny molecular clouds. I’ll describe the observational developments and their interpretation, and I’ll sketch some broad astrophysical implications.

Searching for cosmic dawn from the sub-Antarctic

Mon 11 Dec, 2017 @2.15PM, level 6
Liju Philip, PhD student
University of KwaZulu-Natal

Email: lijuphil[at]gmail.com


Observations of the redshifted 21-cm signal of neutral hydrogen can potentially help us probe the uncharted epochs in the universe’s history. One such epoch is “cosmic dawn,” when the first luminous objects lit up the universe, a few hundred million years after the big bang. The radiation from first stars heated the intergalactic medium, imprinting a characteristic signature in the evolution of the globally averaged 21-cm signal when observed as a function of frequency. The 21-cm spectrum is expected to have a ~100 mK absorption feature at a redshift of approximately 20 (frequency of ~70 MHz). This dip corresponds to the heating of the ambient neutral hydrogen by the first stars and is observationally undetected to date.

We present a new global signal experiment called Probing Radio Intensity at high-Z from Marion (PRIZM). PRIZM consists of two antennas with center frequencies of 70 and 100 MHz operating in the 30–200 MHz frequency band. The instrument observes from Marion Island in the southern Indian ocean, halfway between the continents of Africa and Antarctica. The pristine radio-quiet environment of Marion makes it an excellent location for low-frequency observations. PRIZM observes in dual-polarization mode and uses a Smart Network ADC Processor (SNAP) FPGA board for backend digital signal processing. I will discuss the deployment of PRIZM to Marion during the three-week relief voyage in April 2017. I will present the challenges and lessons learned during the deployment, our assessment of the RFI environment on Marion Island, and preliminary science results from the data collected during the relief voyage. I will also discuss prospects for future radio measurements from Marion that will extend to even lower frequencies.


Wed 7 Mar, 2018 @12PM, level 7
Dr. Stefan Oslowski, Laureate Fellowship Postdoctoral Research Fellow
Swinburne University

Email: stefanoslowski[at]swin.edu.au



Weak Lensing in the Dark Energy Survey

Tue 14 Nov, 2017 @3PM, level 7
Dr. Daniel Gruen, Einstein Postdoctoral Fellow
SLAC / KIPAC / Stanford University

Email: dgruen[at]stanford.edu


The Dark Energy Survey has combined analyses of galaxy clustering and weak gravitational lensing two-point correlation functions in its first year (Y1) of observations. The goal of this is to constrain cosmological parameters from lensing measurements of structure in the evolved Universe. The combination of two-point correlation functions provides information on the amplitude of density fluctuations (S8=0.794+0.029-0.027) and the dark energy equation of state (w=-0.80+0.20-0.22) that is competitive with Planck CMB data. When joint with probes of cosmic geometry, it yields the best measurement of these parameters to date. Besides reviewing these results and the technical advances that facilitated them, I will also present work that provides a DES lensing view of higher than second moments of the matter density field.

Harnessing the Power of Gravitational Lensing

Wed 08 Nov, 2017 @12PM, Geoff Opat room, level 6
Dr. Rachael Livermore, Postdoctoral fellow
University of Melbourne

Email: r.c.livermore[at]astro.as.utexas.edu


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.

Insights into binary black hole formation from gravitational waves

Wed 01 Nov, 2017 @12PM, Level 7
Dr. Simon Stevenson, OzGrav postdoctoral fellow
Swinburne University
Email: spstevenson[at]swin.edu.au

In its first observing run (O1), Advanced LIGO detected gravitational waves from two binary black hole mergers, GW150914 and GW151226, along with a statistically less significant candidate LVT151012. The Advanced LIGO detectors were joined by the Advanced Virgo detector in the recently concluded second observing run (O2). Another two binary black hole mergers, GW170104 and GW170814, have been announced so far from this analysis, with the analysis of the data ongoing. These observations confirmed the existence of merging stellar mass black hole binaries originating in low metallicity environments. How to form merging binary black holes remains an open question theoretically. There are many proposed mechanisms, falling broadly into two families: 1) Isolated binary evolution and 2) dynamical formation in dense stellar environments. We show that comparing the distribution of observed black hole masses and spins to those predicted from population models will allow us to gain insight into how binary black holes form. We examine the measurements of the effective spin parameters for the 5 binary black hole observations published thus far and show that the data already exhibit a mild (2.7 sigma) preference for an isotropic distribution of spins over spins aligned with the binary orbital angular momentum. Alternatively, dimensionless black hole spin magnitudes in these systems could be intrinsically small (average spin magnitude < 0.2), at odds with measurements of black hole spin magnitudes in high mass X-ray binaries. Both of these conclusions have implications for the formation of binary black holes, and the formation of heavy black holes in supernovae.

Probing Fundamental Physics with Strong Gravitational Lensing

Wed 25 Oct, 2017 @12PM, Level 7
Dr. Thomas Collett, Dennis Sciama Fellow
Institute of Cosmology & Gravitation (ICG), Univ. of Portsmouth
Email: thomas.collett[at]port.ac.uk

Local measurements of the expansion rate are in tension with those inferred from observations of the distant Universe. Is this the first sign of new physics or merely a sign of systematic errors within individual probes? This key question remains unsolved, because there are only a handful of established probes. Here I will talk about how strong gravitational lensing offers a new window on precision cosmology, shining a new light on the dark Universe.

I will present strong lensing constraints on the expansion rate of the Universe and the equation of state of dark energy. I will also show how lensing combined with stellar dynamics yields the most precise test to date of the validity of General Relativity on extragalactic scales.

How standard is the standard candle?

Wed 11 Oct, 2017 @12PM, Level 7
Prof. Jeremy Mould, Professor
Swinburne University
Email: jmould[at]swin.edu.au

Over 25 years ago New York Times science writer Dennis Overbye wrote a book oddly titled Lonely Hearts of the Cosmos, narrating the saga of the measurement of distances in the expanding universe, beginning with Edwin Hubble’s first measurements and culminating in a controversy in the scientific literature between Allan Sandage, who had taken up Hubble’s mantle, and Texas astronomer, Gerard de Vaucouleurs. Stranger still, another NYT writer later reported that the film rights had been taken up, and that Tom Hanks had been invited to play Sandage. No movie was made, however, and the controversy was cleared up a few years later by NASA’s Hubble Space Telescope. The age of the expanding universe is now known to an accuracy of a few percent.

There is now a new urgency for increased accuracy in measurements of the Hubble Constant, the misnomer for the current epoch value of the accelerating expansion rate. Stellar Populations and the Distance Scale, sometimes called the distance ladder, as it ascends from the geometric diameter of the Earth’s orbit, has been joined by a rival ladder, descending from the surface of last scattering of the cosmic background radiation. They were expected to meet in the middle, but there seems to be a gap. Or is there? If there is, the standard model of cosmology, the Nobel prize winning ΛCDM model, may be lacking something important. Is it another neutrino, curvature, or a dark matter-neutrino interaction? Right now, the jury is out, and the race for better data is on. Volume simulations indicate that sample variance is not an issue. Are supernovae really standard candles? The OzDES survey is addressing this issue.

The Hubble Constant from Baryon Acoustic Oscillations (BAO) is a standard ruler, rather than a standard candle like supernovae. The ruler is simply the sound horizon at recombination. Simulations tell us that the linear regime for the evolution of structure pertains, and the ruler is unchanged in length in comoving coordinates to a fraction of a percent over the life of the Universe. The Taipan project is expected to achieve 1% accuracy in H0 (1σ) from redshifts of over a million galaxies in the next 5 years. Between the high redshift of BAO and the low redshift of the Local Group, the Hubble Constant can be measured using gravitational lensing with no reference to stars. The H0liCow collaboration has results in agreement with the stellar pops distance scale. A convincing next step would be two independent stellar populations distance scales (Pop I & Pop II) agreeing to 1%.

HI and metal absorption lines during the Epoch of Reionization

Wed 04 Oct, 2017 @12PM, Level 7
Luz Ángela Garcia, PhD student
Swinburne University
Email: lgarcia[at]swin.edu.au

In this work, we study the epoch of Reionization (EoR) with metal absorption lines in quasar spectra at high redshift, using high resolution hydrodynamical simulations (an improved version of GADGET-3). For this purpose, we set up the physical conditions of the intergalactic medium (IGM) at the redshift of the EoR, and we post-process the simulations to implement a uniform UV ionizing background for quasars and galaxies (Haardt-Madau 2012), the metal ions with CLOUDY 8.1 and HI self-shielding prescription (Rahmati et al. 2013). We use Voigt profile fitting to compute the column densities of the ions from the synthetic spectra and obtain a statistical distribution of the absorbers. This procedure allows us to study the evolution of the state of the IGM at high redshift, compute the cosmological mass density of CIV and HI and other ions. Our simulations produce absorbers properties that are in good agreement with observations in the literature, especially for the high ionization species.

Furthermore, we are able to reproduce an observed example of an LAE galaxy-CIV absorber pair at z=5.7, proving a physical insight into such systems beyond the limit of current observations. Finally, we vary of the uniform UVB at z~6, and compare directly with observations of different metal ions, in order to constrain the ionizing background at the tail of Reionization.

Stochastic gravitational waves in the reach of aLIGO?

Wed 27 Sep, 2017 @12PM, Level 7

Prof. Csaba Balazs, Professor
Monash University
Email: csaba.balazs[at]monash.edu

Based on a scalar singlet extension of the Standard Model of elementary particles, I present a scenario that features stochastic gravitational waves potentially observable by aLIGO.

The many lives of AGN II: the formation and evolution of radio jets and their impact on galaxy evolution

Wed 20 Sep, 2017 @12PM, Level 7
Prof. Darren Croton, Professor
Swinburne University
Email: dcroton[at]astro.swin.edu.au

In this talk i describe new efforts to model radio AGN in a cosmological context using the SAGE semi-analytic galaxy model and a number of large cosmological N-body simulations. Our new method tracks the physical properties of radio jets in massive galaxies, including the evolution of radio lobes and their impact on the surrounding gas. Unlike the previous efforts of Croton et al. 2006, we now self consistently track the cooling-heating cycle that significantly shapes the life and death of many types of galaxies. Adding jet physics to SAGE adds new physical properties to the model output, which in turn allows us to make more detailed predictions for the AGN and galaxy populations, and build customised AGN-focused mock survey catalogues for comparison with observations.

Shining a light on planetary processes

Wed 13 Sep, 2017 @12PM, level 7
Dr. Helen Brand, Scientist – Powder Diffraction
Australian Synchrotron

Email: helen.brand[at]synchrotron.org.au


Jarosites and related minerals are of great importance to a range of mineral processing and research applications. They are used in the removal of iron species from smelting processes; they occur in metal bioleaching systems, and in the desulphurisation of coal; they are present in acid mine drainage environments.

There has been a recent resurgence in interest in jarosite and associated minerals since their detection on Mars by the MER rover Opportunity. In this context, the presence of jarosite has been recognised as a likely indicator of liquid water at the surface of Mars in the past and it is hoped that their study will provide insight into the environmental history of Mars.

Acid sulfate soils cover large areas of the Australian coastline and are likely to be a major constituent of the Martian environment. The oxidation of acid sulfate soils, coupled with potential release of heavy metals and acidic groundwaters, can have serious consequences for fragile ecosystems. Understanding these sediments will provide insight into the biogeochemical processes that affect the lifetimes of transient mineral species on Earth, and may be used to better understand soil acidification, contaminant mobility at sites affected by acid and metalliferous drainage, and even constrain past weathering and putative biosignatures on Mars.

Knowledge of the behaviour of jarosite minerals under the actual conditions that they are found in is crucial to understanding their potential environmental impacts on both Earth and Mars. To this end, we are engaged in a program to study the formation, stability and alteration of jarosite minerals using a complementary suite of in situ synchrotron and neutron techniques.

After GW150914: gravitational-wave astronomy in the era of routine detection

Wed 30 Aug, 2017 @12PM, level 7
Dr. Eric Thrane, Senior Lecturer
Monash University

Email: eric.thrane[a]monash.edu


The first detection of gravitational waves from merging black holes (dubbed GW150914) ushered in the era of observational gravitational-wave astronomy. Since this seminal discovery, Laser Interferometer Gravitational-wave Observatory (LIGO) has announced the detection of three additional confirmed merger events—four if we include the marginal LVT151012. As the sensitivity of our detector network improves, detections will become routine. Indeed, at design sensitivity, LIGO may be detecting several events every week. This glut of gravitational waves presents us with new opportunities. I discuss a few of the research directions that have emerged in the wake of LIGO’s first detections including observationally-driven analysis of binary black hole formation channels, measurements of gravitational-wave memory, and tests of the famed no-hair theorem.

Modelling thermonuclear supernovae: how to blow up a white dwarf star

Wed 09 Aug, 2017 @12PM, level 7
Dr. Stuart Sim, Lecturer/Associate Investigator (SkyMapper)
Queen’s University Belfast, UK

Email: s.sim[at]qub.ac.uk


Aside from being spectacular displays in their own right, Type Ia supernova explosions have a key role in measuring the expansion history of the Universe and synthesizing the iron group elements. But what is their origin? That Type Ia supernovae arise from exploding white dwarfs is relatively well-established but the manner in which the explosion is ignited and how this can be determined from what we observe remain hotly debated issues.
I will discuss the theoretical modelling of Type Ia supernovae with particular focus on how radiative transfer simulations can be used to test explosion scenarios. I will argue that understanding the diversity of thermonuclear supernovae requires us to investigate a variety of different progenitor scenarios. Specifically, I will present recent results from our work on both Chandrasekhar mass white dwarf explosion scenarios and sub-Chandrasekhar mass models.

Galaxies at Cosmic Dawn: Exploring the First Billion Years with Hubble and Spitzer – Implications for JWST

Wed 02 Aug, 2017 @12PM, level 7
Prof. Garth Illingworth, Professor
University of California Santa Cruz
Email: gedi[at]ucolick.org


Hubble has revolutionized the discovery and study of very distant galaxies through its deep imaging surveys. Together the HST WFC3/IR and ACS cameras have opened up the exploration of the universe in the first billion years after the Big Bang. I will discuss what we have learned about the earliest galaxies during the reionization epoch at z>6 from the remarkable HST and Spitzer imaging surveys (e.g., HUDF/XDF, GOODS, HUDF09/12 and CANDELS), as well as surveys of galaxy clusters like the Frontier Fields (HFF). Lensing clusters provide extraordinary opportunities for characterizing the faintest earliest galaxies, but also present extraordinary challenges. Together these surveys have reliably established the volume density of galaxies in the first billion years down to extremely faint levels around -14.5 mag. The results from deep UV luminosity functions from Hubble, combined with the recent results from Planck, indicate that galaxies dominate the UV ionizing flux that reionized the universe. Some of the greatest surprises have come from the discovery of very luminous galaxies at z~8-11, around 400-650 million years after the Big Bang. Spectroscopic followup of these very rare, bright galaxies has confirmed redshifts from z~7 to z~11, and revealed, surprisingly, strong Lyα emission near the peak of reionization when the HI fraction in the IGM is high. The small sizes of galaxies at high redshifts, from analysis of the HFF cluster samples, reveal objects that, remarkably, are as small as globular clusters and dwarf galaxies. The recent confirmation of a z=11.1 galaxy, just 400 million years after the Big Bang, by a combination of Hubble and Spitzer data, pushed Hubble into JWST territory, far beyond what we ever expected Hubble could do. Twenty years of astonishing progress with Hubble and Spitzer leave me looking to JWST to provide even more remarkable exploration of the realm of the first galaxies at “Cosmic Sunrise”. The latest results on the sizes of distant galaxies, on the star formation rate density at z~10 and from Planck indicating that reionization began around z~10 together have significant implications for the detectability of the “first galaxies” with JWST.

Number of posts found: 41