Descriptions of Current PhD Research
Our standard cosmological model assumes that the Universe is homogeneous and isotropic, which forms the basis of all modern cosmological measurements. However, given the serious problems with the standard cosmological model such as the need for dark energy, there has been recent debate about the effect of the inhomogeneities traced by the clusters and voids that fill the current Universe.
These features create curvature gradients and differential expansion in the context of general relativity that should affect our cosmological measurements. My PhD quantifies the amplitude of these effects, focussing on current and future data from peculiar velocity surveys, galaxy redshift surveys and dark matter simulations. Firstly, the potential of peculiar velocity surveys to test various aspects of the cosmological model will be simulated, to guide what topics may prove most fruitful. Secondly, I will undertake a detailed investigation of cosmological "backreaction" from inhomogeneities. What is its observational signature, and how might it be distinguished from non-linear growth of structure in the standard cosmology?
We will investigate simple backreaction models, and explore modelling backreaction within N-body simulations. Finally, galaxy redshift surveys such as the WiggleZ Dark Energy Survey will be re-analyzed in the context of inhomogeneous cosmological models, to test whether such models are supported or disproved.
Anna Sippel - Metallicity Effects on Simulated Globular Clusters
The goal of my thesis is to follow the evolution of globular cluster models with varying initial parameters, mainly metallicity, up to the Hubble time and beyond. As the metallicity affects the rate of stellar evolution of each individual star, an effect on the whole cluster is expected. I'm investigating the influence of metallicity on structural parameters such as the effective radius. To evolve the models, we use the direct N-body code NBODY6 (Aarseth 2003), which is the most advanced code to evolve star clusters. We make use of the recent possibility to run this code on graphics processing units located here at Swinburne. Only the speed-up in computational time compared to using conventional CPUs makes this project possible.
Bililign Dullo - Light Profile Models for the Structural Analysis of Early-Type Galaxies.
The stellar distributions in galaxies have played a vital role in guiding our understanding of the galaxies themselves. Following Hubble’s (1930) innovative work on elliptical galaxies brightness profiles, there have been many studies on galaxy centers using their radial surface brightness distribution. The main focus of my PhD thesis is to unveil the secrets of galaxies’ centers through an analysis of their 2-dimensional stellar distribution and 1-dimensional brightness profile. Several scientists have advanced different models as a possible avenue to reproduce the HST-observed surface brightness profiles of early-type galaxies at distance ~ 10 - 100 Mpc. I am currently using the Sersic and core-Sersic models for fitting galaxies' brightness profiles, and also conducting a close investigation on the central light deficits (fingerprints of the gravitational sling shot effect of coalescing Supermassive Black Holes) and light excesses (which signature the presence of additional nuclear light components: e.g. Nuclear star clusters, stellar disks). This work will eventually provide new insights in to the galaxy formation process.
Frank Pignatale - Physical Chemistry of protoplanetary disks
The goal of my Ph.D is to improve the knowledge of the physical chemistry in protoplanetary disks with the study of the behaviour of solids phases that characterize the chemical composition of the ﬁrst grains formed in the early stages of the protoplanetary disk life. The deﬁnition of the thermodynamical properties of these compounds, together with their chemical paths, is important in better understanding the formation of our solar system, as well as the observational evidence from protoplanetary disks, and can provide clues on the possible bulk composition of the exoplanets that have formed in widely diﬀerent environments.
Gonzalo Diaz - Connecting star formation and its products in the early universe.
The production of metals by the first stars in the universe is closely related to the emission of Lyman continuum photons responsible for the cosmic reionization of hydrogen which could have started at z > 15 and continued until z ~ 6. Recent observation of high resolution spectroscopy had revealed the presence of metals in the most distant IGM trough the detection of absorption systems in spectra of background QSOs. The most common and easiest to recognize is the CIV doublet. Even though these absorption systems are associated with star forming galaxies, whether this enrichment of the IGM occurs from super galactic winds or the dynamical disruption of small mass galaxies is still a matter of debate. We will use FORS2 multi-object spectroscopy (VLT) to measure the redshift of two candidate z > 5.5 galaxies which are close enough to the line of sight towards the QSO SDSS J1030+0524 to be responsible of the CIV absorption detected in the spectrum of the QSO. If they could have produced the absorption or not will support different scenarios and provide constraints on the physical extend of the enriched, ionizing outflow of the galaxies. Furthermore, cosmic reionization is expect to be a patchy process. A highly variable ionization state is detected at 5 < z < 6 but there is no agreement in whether or not the largest overdensities should be the first or last to be permanently ionized. Then, we will use the Supreme Cam/Subaru to image field with highly ionized absorption line systems at z ~ 5-6. Studying the density of galaxies at z ~ 5-6 will help us to discriminate between theoretical models that predict regions of ionized IGM should correspond an under/over-density of galaxies.
Guido Moyano Loyola - The Chemical Evolution of Globular Clusters Unravelled
Since the early '60s N-body problems have been studied using numerical simulations. As the computational technologies improved over time, astronomers could start to think in terms of more realistic simulations of stellar clusters. Our understanding of the physics of the stars was also improved as well thanks to the developments in stellar evolution and nucleosynthesis conducted during that time.
It was then obvious that we could not think of gravity as the only factor regarding stellar clusters evolution, we should add stellar evolution to our models (not only for single stars, but binaries too).
One successful advance on this topic was the SSE (Single Stellar Evolution) and BSE (Binary Stellar Evolution) codes made by Hurley et al., 2000 and Hurley et al., 2002. These codes were implemented first in Nbody4 and then in Nbody6.
Within my PhD project a detailed description of nucleosynthesis will be added to these state-of-the-art N-body codes that follow the dynamical, stellar and binary evolution within a stellar cluster. This will enable us to build a self-consistent theory of the chemical evolution of star clusters for the first time.
With this modelling capability we will:
* directly quantify the composition of ejected gas in the dense stellar environment of a star cluster and improve our understanding of the abundance patterns of the various constituent stellar populations
* provide reliable information for models of galactic chemical evolution
* probe the formation mechanism of globular clusters, particularly the increasing obsercvational evidence of multiple generations of stars produced during the cluster formation phate
* quantify the contribution from binaries and open clusters to the population of chemically anomalous stars in the Galactic disk, required information for Galactic Archaeology projects that utilise chemical tagging.
The N-body simulations of globular clusters evolution (including nucleosynthesis) will be performed on the GPU hardware of the new gSTAR supercomputer at Swinburne.
The nucleosynthesis component will be conducted in collaboration with John Lattanzio at Monash University who will provide the results of detailed calculations for AGB stars and type II Supernovae. In the latter stages of the project the output of the star cluster models will be interfaced with semi-analytic and detailed models of galaxy evolution (provided by Darren Croton at Swinburne University) to explore aspects such as abundance variations, e.g. metallicity gradients, related to globular clusters in a range of galaxy environment.
There is strong evidence that the power sources for quasars are supermassive black holes lurking in their host galaxies. However, the theoretical links between these black holes and their hosts are not fully understood yet. Cosmological microlensing, the study of how compact objects magnify a background source, provides a unique probe for quasar properties. Monitoring of multiply-imaged, microlensed quasars allows observations of quasars at physical scales orders of magnitude smaller than the resolution of our best telescopes. In this project, I am going to use microlensing simulations to explore realistic quasar models.
A critical component of this project will be the use of a brand new supercomputing facility at Swinburne, called gSTAR : the GPU Supercomputer for Theoretical Astrophysics Research, with a processing capability of over 100 Teraflop/s. A major project planned for gSTAR is a high-resolution gravitational microlensing parameter survey. My thesis will include undertaking this survey, analyzing the results and making predictions relevant to future major optical all-sky surveys, which are expected to find thousand of new microlensed quasars in the years ahead.
Helga Denes - Global HI properties of galaxies in the Southern Sky
The evolution of galaxies depends on both internal and external factors - such as mass, and environment respectively. It is becoming increasingly apparent that even a small over-density in the local environment (such as a group) can affect the evolutionary track of a galaxy. This PhD project will investigate the effect of environment on the evolution of spiral galaxies, specifically using the neutral
hydrogen (HI) content of a galaxy as a tracer for environmental effects. The student will use the recently re-processed southern-sky HIPASS dataset, matched with optical datasets such as 6dF to trace the HI content of galaxies across the whole of the southern sky. One of the outcomes of this project will be a global HI content map, which will show where spiral galaxies are HI deficient - this will be correlated with the local environment, and compared with the latest
simulations on galaxy evolution.
Kathrin Wolfinger - The effect of environment on the evolution of nearby gas-rich spiral galaxies
Galaxies are found in filamentary structures, groups and clusters. Membership of a group or cluster affects the evolution of a galaxy significantly and I am studying several regions in detail, including a newly-forming cluster (Ursa Major cluster) and a group infalling into a young cluster (NGC 4930 group), to find the first signs of interaction and transformation occurring in the spiral galaxies in dense regions. Because the neutral hydrogen (HI) traces the large scale disks of spiral galaxies, gravitational forces from neighbors and ram pressure stripping by the intra-group/cluster gas will affect their HI morphology. The Ursa Major cluster and NGC 4930 group are mostly made up of gas-rich spirals and are perfect examples to search for these signs of interaction and transformation.
Max Bernyk - Galaxies formation and evolution
I am studying galaxy formation and evolution using computer simulations and by making them comparable to observations. In particular I am interested in Super Massive Black Holes accretion mechanisms and feedback. Modern simulations produce enormous amounts of data, as well as observations, therefore my work involves large datasets, data-mining and high-performance computing. As a member of Theoretical Astrophysical Observatory team I am working on the production of mock catalogues for CANDELS and WiggleZ surveys.
Mark Durre - Active galactic nuclei: an examination of their physical environment and properties.
Pierluigi Cerulo - The Build up of the Red Sequence in High Redshift Galaxy Clusters
The aim of my PhD thesis is to understand the processes that contribute to the build up of the red sequence in galaxy clusters by studying how the properties of galaxies, in a sample of 10 high redshift clusters, vary as a function of their location on the red sequence. The properties of galaxies (morphology, mass, metallicity, star formation rate and star formation history) will be measured using high resolution HST and ground based NIR data and existing and upcoming high S/N spectroscopic observations with Keck/LRIS. The GOODS data will be used for the comparison with the field, at the redshift of the clusters, while the Wide-field Nearby Galaxy-cluster Survey (WINGS), which covers the redshift range 0.03 < z < 0.08 will be used as a comparison sample for the local universe.
Sreeja Kartha - Wide-field studies of extragalactic globular clusters
My thesis intends to better understand the extragalactic globular cluster (GC) populations, as a probe to study the galaxy formation scenarios of early-type galaxies.
The globular cluster systems of galaxies can be extended up to larger radii than the galaxy light. The study of GC systems within small galactocentric radius can reveal information about the local GC properties but not their global properties. Hence to get a more accurate picture of GC properties, galaxy studies using wide-field imaging is essential. For this, a survey of early-type galaxies of different masses is undertaken using wide-field imaging from Subaru and Canada France Hawaii Telescopes. This work aims to provide new constraints on galaxy formation and evolution from the globular cluster systems.
Syed Uddin - My PhD topic is on improved constrain on cosmology using type Ia supernovae hosted in early-type galaxies.
The theme of my PhD is to work on both instrument development and observational studies. A key problem in cosmology is finding the epoch in time when the first structures in the Universe collapsed to form the first stars. The UV from these stars ionized the neutral hydrogen in the universe left over from the Big Bang, a process called 'reionization'. Current observations have pushed this epoch back to z>7. Accessing this epoch required deep NIR observations because all the emission from candidate objects is redshifted out of the optical region. Such observations are difficult because of the bright airglow from the night sky at these wavelengths.
At Swinburne we are developing a new technology photonic filter which if successful could suppress this emission and make existing telescopes 10-20x more sensitive. The focus of this PhD project will be to work on the design, development and testing of this filter. Along the way I will also look into other photonic devices that can enhance performances of astronomical detectors.
Tyler Evans - Robust Constraints on Varying Fundamental Constants from QSO Absorption Systems
I work to answer the question “Are fundamental constants actually constant?” Fundamental constants refer to values such as alpha, the fine structure constant, and mu, the ratio of the proton to election mass. These values, which have been assumed as constants are necessary in the Standard Model of particle physics but we have no understanding as to where they come from or why they are constants. Earth-based laboratory tests have constrained the variation of these values very strongly but only in a small section of space-time (on the Earth and in human lifetimes).
I’m part of a group using quasar absorption systems to measure the value of fundamental constants over large scales in both distance and time. Preliminary results suggest a spatial dipole in alpha across the sky but these results require significant checking before any extraordinary claims can be made. One aspect of checking in which I am heavily involved is in understanding and correcting for any systematic errors from the telescopes we use.
Themiya Nanayakkara - MOSFIRE spectroscopy of galaxies at Cosmic Noon
Using precise photometric redshift pre-selection from ZFOURGE and deep imaging
from Hubble Space Telescope in this PhD project an efficient study will be done
with MOSFIRE on galaxy populations across a range of cosmic environments (from ﬁeld to rich cluster). Galaxy spectroscopy provides the fundamental redshift distance and cosmic environment measurements which underpin our understanding of cosmic evolution. It will allow us to measure the co-dependence of mass and star-formation via star-formation and metallicity diagnostics and measure galaxy halo kinematics via velocity dispersion and rotation measures. New imaging data from HST (the CANDELS survey) will provide high-resolution imaging to elucidate the physical structures (disks, bulges, star-forming clumps) and it's connection to the spectroscopic measures.
Vincenzo Pota - The formation scenario of extragalactic globular clusters
I’m studying the kinematics and dynamics of extragalactic globular clusters (GCs) in nearby galaxies. By exploiting the DEIMOS multi-spectrograph and the Suprime-Cam camera for imaging, I reconstruct the kinematic properties of a dozen galaxies from 1 up to 10 effective radii where the diffuse galaxy light is too faint to return kinematic information. Eventually, I estimate the baryonic and non-baryonic matter content, to test the Lambda-CDM cosmological paradigm. The most intriguing properties of extragalactic GCs is their bimodality in colour, perhaps related to different formation mechanisms of the host galaxy. The goal of my PhD is to reveal how the globular cluster subpopulation formed and to understand what they can tell us about the assembly of galaxies.