Dr. Luke Davies
Title: Star Formation, Mergers and the Assembly of Stellar Mass in Galaxies
Abstract: Since the first stars and then galaxies formed the Universe has been an immense factory converting neutral gas into stellar material. The distribution of this stellar material is key to our understanding of galaxy formation and evolution as it is the primary baryonic component we can observe in galaxies over the last 13Gyr. However, the changing distribution of stars at a given epoch is dependent on many different processes such as: i) in-situ star-formation rates, ii) merger rates, iii) the neutral gas reservoirs available for future star-formation episodes, iv) the effect of galaxy-galaxy interactions on both star-formation and neutral gas content and v) AGN activity. These processes occur in different measures to all galaxies over the history of the Universe, ultimately resulting in the distribution of stellar material we see today. If we wish to understand the assembly of stellar mass in the Universe we must aim to probe all of these process, and build a complete and consistent picture of their interplay over cosmic timescales.
In this seminar I will discuss recent results from the Galaxy And Mass Assembly (GAMA) survey, probing the assembly of stellar mass though both in-situ star formation (as traced by multiple SFR indicators) and interactions (both mergers and interaction induced star-formation) - in galaxies spanning ~4 decades in stellar mass. I will discuss upcoming HI surveys which are aligned with the current state-of-the-art multi-wavelength, spectroscopic surveys - allowing us to simultaneous probe both star-formation and neutral gas reservoirs in a consistent and statistically robust sample of galaxies. Lastly, I will discuss how large area surveys of the coming decade, such as the Wide Area VISTA Extragalactic Survey (WAVES), will help revolutionise our understanding of the assembly of stellar mass is galaxies.
Dr. Jessica Chapman
Title: Maser Observations from Evolved Stars
Abstract: Towards their end of their lifetimes, low and intermediate-mass stars lose a large fraction of their mass through circumstellar winds. The highest mass-loss rates occur from Asymptotic Giant Branch (AGB) stars. These are long-period variable stars, with periods between approximately 100 and 3,000 days and luminosity's that are typically 10,000 times higher than the sun.
In this talk I will show how maser observations from SiO, H2O and OH molecules can be used to study the circumstellar envelopes of AGB stars and the so-called 'post-AGB' stars to provide a detailed understanding of their structure and kinematics. The relatively rare post-AGB stars are in a short-lived transition stage between AGB stars and planetary nebulae. Their maser properties are strikingly different to those of the AGB stars with a large fraction showing beautiful bipolar or butterfly-wing type geometries similar to those of planetary nebulae. From maser and infrared studies it seems likely that, for single stars, the shaping of non-spherical planetary nebulae winds begins early in the post-AGB stage of stellar evolution.
Dr. Angel Lopez-Sanchez
Title: Exploring the HI-metallicity-galaxy mass connection with CALIFA
Abstract: During the last years a "Fundamental Relationship" between stellar mass, star-formation rate (SFR) and metallicity has been observed in star-forming galaxies. Here we present a study of such relation using data derived from the CALIFA (Calar Alto Legacy Integral Field Area) survey, but also including the data of the neutral gas mass, that have been obtained from the literature using available measurements of the 21 cm HI line. Our study, that follows a Principal Component Analysis (PCA), suggests that it is the gas mass (and not the SFR) which is driving this Fundamental Relation. We will define the Baryonic Fundamental Plane for star-forming galaxies in the space formed by stellar mass, oxygen abundance (as proxy of metallicity) and the gas-to-star mass ratio. This relationship has been recently predicted by cosmological hydro-dynamical simulations. We will discuss the implications of such Baryonic Fundamental Plane in the context of galaxy evolution and its role in the on-going and future large galaxy surveys.
Dr. Caroline Foster
Title: Deciphering the formation of early-type galaxies using large scale dynamical stellar maps
Abstract: As part of the SAGES Legacy Unifying Globulars and Galaxies Survey (SLUGGS), we have obtained large scale (out to 2.6 effective radii), spatially resolved stellar kinematic maps for over 25 early-type galaxies. I will present these kinematic maps, kinemetry fits and variations in the angular momentum as a function of galactocentric radius. Changes in the dynamical support (rotation versus pressure) as a function of radius in multiple systems emphasize the need to survey the faint outskirts in order to obtain a complete picture. These results are used to infer the individual assembly history of the galaxies in our sample.
Title: New halo stars of the Galactic globular clusters M3 and M13 in the LAMOST DR1 Catalog
Abstract: M3 and M13 are Galactic globular clusters with previous reports of surrounding stellar halos. We searched for members and extratidal cluster halo stars within and outside of the tidal radius of these clusters in the LAMOST Data Release 1. We primarily used radial velocity to select candidate stars, but also considered photometry, stellar parameters and proper motions to clean our sample. We found seven probable cluster members (inside the tidal radius) of both M3 and M13 respectively. In M3 we also identified eight probable extratidal cluster halo stars at distances up to ∼9.8 times the tidal radius of the cluster, and in M13 we identified 12 probable extratidal cluster halo stars at distances up to ∼13.8 times the tidal radius. These results support previous indications that both M3 and M13 are surrounded by extended stellar halos. We compared the destruction rates corresponding to the observed mass loss with destruction rates predicted by theoretical studies and found that they are, generally, significantly higher than the predictions. If these candidate stars are confirmed as ex-cluster members with planned high-resolution spectroscopic follow-up observations, this will help constrain theoretical studies of globular cluster destruction rates as well as their contribution to the Galaxy's stellar halo.
Dr. Jesse van de Sande
Title: Revisiting galaxy classification with SAMI through high-order stellar kinematics
Abstract: The introduction of visible integral field spectrographs in the last decade let to major developments in the kinematic classification of galaxies. From two-dimensional stellar kinematic measurements, the SAURON and ATLAS-3D survey showed that galaxies can be classified as fast and slow rotators. The very different dynamical properties of these groups suggest that there is more than one formation path for creating early type galaxies. Recent cosmological hydrodynamical simulations suggest, however, that in order to better understand the assembly and merger history of galaxies, the deviations from a Gaussian line of sight velocity distribution have to be studied. In particular the high order kinematic moments h3 (skewness) and h4 (kurtosis) of the lines can be used to decode a galaxy's cosmological assembly history. In this talk, I will assess these result by using stellar kinematic measurements from the SAMI Galaxy Survey. From the high order moments, we have developed a new method for kinematically classifying galaxies. I will compare our new kinematic classes to other global galaxy properties, and show that this method has real potential for linking the high order moments to the type of mergers galaxies experienced in their past.
Associate Professor Daniel Price
Title: Gaps, bananas and holes: Planet formation in action?
Abstract: Brand new images from the Atacama Large Millimetre/Submillimetre Array and the SPHERE adaptive optics instrument on the Very Large Telescope are showing us, for the first time, the processes of planet formation `in action’ in nearby discs. The most spectacular images have shown us dust discs riddled with gaps together with numerous `banana’ structures thought to be explained by dust trapping in vortices. Furthermore, most discs as they age appear to have `holes’ or cavities in the central regions. Whether or not these are genuine signatures of planet formation — or not — may totally revolutionise our understanding of how (and how quickly) planets are formed. I will highlight our recent work to try to model mixtures of dust and gas in 3D hydrodynamics simulations, and how we have been using this to provide urgently needed theoretical interpretation to the observed gaps and bananas, and how they might relate to newborn planets. I will also discuss how such massive discs might form, in particular when magnetic fields are involved and the role played by non-ideal MHD effects including resistivity, Hall currents and ambipolar diffusion.
Dr. John G. Spray
Title: High-speed impact:From Planetary Science to Materials Engineering
Abstract: This presentation will describe how research in the Earth and Planetary Sciences concerning impact cratering processes has led to the establishment of a High-Speed Impact Lab in Canada. The lab can re-create conditions similar to those experienced by rocks and minerals on solid planetary surfaces subject to hypervelocity impact by asteroids. In addition, the test equipment can be deployed to evaluate and develop protective materials for the defence, aerospace and space sectors. The presentation will discuss examples of both academic and applied research associated with high-speed impact technologies based primarily on light-gas gun systems. Alternative launch techniques will also be discussed – we need to achieve 15 km/s under controlled conditions – this is challenging but feasible.
Title: Using the sub-giant branch to constrain the star formation history of intermediate-age clusters
Abstract: The presence of extended main-sequence turn-off (eMSTO) regions in intermediate-age, 1–2 Gyr-old star clusters in the Large and Small Magellanic Clouds is often interpreted as resulting from extended star-formation histories (SFHs) that last ≥ 300 Myr. This strongly conflicts with the traditional view of stellar clusters, which are thought of as single-aged stellar populations. In this talk, I will show our investigation into these issues by exploring the morphology of the sub-giant branch (SGB) of LMC and SMC clusters. We find that for most cases, the width of the SGB favors the single-aged stellar population interpretation and rules out an extended SFH. For clusters that have a very low escape velocity, they have unlikely undergone significant mass loss at an early stage, thus indicating that they may lack the capacity to capture most of their initial, expelled gas from stellar evolutionary processes.
Dr. Nicholas Scott
Title: Extragalactic Archaeology: uncovering galaxy formation histories with SAMI
Abstract: The stellar population of a galaxies encodes a record of its entire formation history. This history can be unraveled using optical spectroscopy combined with modern stellar population modelling techniques. The SAMI Galaxy Survey is a large, spatially resolved spectroscopy survey of galaxies spanning a broad range in mass, environment and morphology. Using SAMI data, I show how the age, metallicity and abundance patterns of the local galaxy population depend on their structure and environment. Taking advantage of SAMI's spatially resolved data, I extend this analysis to radial gradients in stellar age and metallicity, and examine how stellar population gradients can constrain possible formation scenarios for different morphologies and environments.
Dr. Peter Tuthill
Title: Syzygys, Stardust and the sizes of stars: Adventures in space from starman to starshot
Abstract: This talk will discuss results and plans for unique imaging experiments aboard several space missions. These occupy an unusually wide range of niches from existing spacecraft, major future facilities, low-cost micro-satellites and speculative dreams at the boundary of science fiction.
Title: The terrifyingly potential (and wondrous problems) of radio-based Cosmology
Abstract: The Evolutionary Map of the Universe (EMU) is an upcoming radio survey planned to start early next year on the ASKAP telescope. Surprisingly EMU (which is primarily a galaxy evolution survey) is predicted to have serious potential for constraining the cosmological parameters of Dark Energy and Modified Gravity/Dark Matter. Covering 80% of the sky down to a sensitivity of 10uJy, EMU will produce on the order of 70 million radio galaxies for study. Our team has begun development on the EMU Cosmology pipeline in order to turn this huge number of sources into measurable cosmological parameters in a timely fashion. We present here new results from our early test fields which show good agreement to previously published work. Furthermore we identify several key issues that need to be considered should EMU wish to reach its full cosmological sensitivity.
Dr. Ryan Shannon
Title: Fast radio bursts and the magnetization and turbulence of the cosmic web
Abstract: Fast radio bursts (FRBs) are a new population of millisecond-duration apparently extragalactic radio pulses. Little is known about the bursts because of poor localization and relatively low flux density. If they originate at cosmological distances, they are produced by a fantastically luminous emission mechanism and promise to be valuable probes of the tenuous intergalactic plasma that dominates the baryonic content of the Universe. In this talk I will discuss two FRBs that we have recently detected in real time with the Parkes telescope. The first FRB was detected toward (but beyond) the Carina dwarf spheroidal galaxy and shows evidence radio afterglow (similar to those seen from gamma-ray bursts) with an unusual optical counterpart. The second was detected toward (but beyond) a galactic millisecond pulsar and is the brightest and least dispersed FRB yet detected. The high flux density allows us to directly localize the burst and place a lower limit on its redshift. I will discuss how this burst’s Faraday rotation and diffractive scintillation pattern can be used measure the magnetization and turbulence of the intercluster medium. I will conclude by motivating revised strategies for future surveys for FRBs.
Dr. Tayyaba Zafar
Title: Distant Gamma-Ray Bursts as tracers of dust
Abstract: Long duration Gamma-ray bursts (GRBs) are powerful spectacles since the Big Bang. The long duration GRBs are associated with the death of massive stars, have simple intrinsic power-law spectrum, and their cosmological occurrence stretches out to the epoch of reionization, a time when the first galaxies and stars were forming. These advantages make GRBs potentially unique and effective probes to study dust extinction in the Universe over broad range of redshifts. The knowledgeof the dust properties in GRB host-galaxies is very usefulto understandthe interstellar medium of high redshift galaxies and the cosmic star-formation history. The X-ray to optical spectral energy distributions of GRBs are used to determine the dust extinction in the GRB local environment. The results indicate dust content at various redshifts and the preferred extinction curve for GRBs. However, a large diversity of extinction curve shapes is seen in GRBs. This suggests that GRBs occur in diverse environments. The presence of various extinction laws hints the nature of the dust (grain population, sizes and composition), varying from silicates to carbonaceous grains.
Dr. Chris Lidman
Title: OzDES reaches the half way mark
Abstract: In collaboration with the Dark Energy Survey, OzDES is using the AAT to derive what will be the tightest constraints yet on the dark energy equation-of-state parameter. While probing dark energy is the prime aim of the survey, the observing strategy enables us to conduct a number of other investigations, such as measuring the growth of black holes from 12 billion years ago to the present day. OzDES is now halfway through its allocation of 100 AAT nights. In this talk, I will describe the OzDES project, its scientific aims, and present some preliminary results.
Dr. Lee Spitler
Title: The Huntsman observing systems: ultra-faint astronomical imaging from the ground and space
Abstract: I will motivate and describe two new observing systems: the ground-based Huntsman Telephoto Array and the space-based Australian Space Eye or "Huntsman in Space". These observatories are optimised for capturing information about diffuse, spatially extended faint astronomical sources. Through the use of refracting lenses, we are able to push well below the systematic limits of conventional reflecting telescopes. This allows us to see billion-year old stellar structures in galaxies in order to deduce their formation history. The Space Eye will allow us to measure the total luminosity of the universe at optical wavelengths of light. I will also briefly describe how satellite miniaturisation is enabling a new generation of space-based research facilities.
Prof. Geoffrey C. Clayton
Title: Continuous Dust Formation in Core-Collapse Supernovae?
Abstract: In the last decade, many studies of dust formation in core-collapse supernovae (CCSNe) have found only small amounts, ~10^-3 solar masses, during the first three years after the explosion. This is far less than the amount needed to account for the large masses of dust seen in some high redshift galaxies. However, the recent discovery of up to one solar mass of cold dust in the ejecta of SN 1987A, confirmed by ALMA, has caused a complete re-evaluation of dust formation in CCSNe. It has been suggested that the CCSNe are continuously forming dust so that by the time they are about 25 years old they will have dust masses similar to SN 1987A. However, there is a wide time gap between the CCSNe that have been studied recently and SN 1987A. We are using Gemini/GMOS and VLT/XSHOOTER to obtain spectra of a large sample of CCSNe, between 4 and 50 yr after explosion, to test this suggestion. We are also interested in how the nature of the massive-star progenitor affects dust formation in the SN ejecta and, in particular, whether there was a large outburst forming a circumstellar shell prior to the explosion of the star. We are hoping to get a better understanding of pre-supernova mass-loss, and the links between the progenitor and its subsequent dust production and evolution.
Prof. Chris Tinney
Title: A New Age for Exoplanets is Coming
Abstract: The Kepler mission has revolutionised our understanding of the prevalence of small planets in our Galaxy - almost every star seems likely to host a planet of a few Earth-masses of smaller in orbits shorter than a few hundred days. It has also shown us that the range of planetary system architectures is far larger than we could have imagined, and that our Solar System may *not* be a typical end-product of planet formation.
Annoyingly though, almost every one of the thousands of Kepler planets orbit stars so faint, that they can’t be further observed in any meaningful manner. we can’t get masses to complement Kepler’s size measurements (and so we don’t know densities). We can’t look for additional gas-giant planets on longer period orbits. And we can’t try to measure the “transit spectra” of these planets to probe their atmospheres.
But that will all change in late 2017, when NASA launches its TESS mission which will find thousands of planets more than an order of magnitude brighter than the Kepler planets. And it will be finding them in the southern
The Exoplanetary Science at UNSW team is racing to have new facilities available in time to exploit this incredible opportunity, and I’ll tell you what we are planning on doing.
Title: The rise and fall (and rise again) of NGC1275
Abstract: Recent observations have shown that the properties of the dense intracluster gas cooling in the cores of clusters of galaxies are significantly affected by AGN activity in the central brightest galaxy.
I will review these observations and focus on the most nearby example of this AGN Feedback from NGC1275 at the core of the Perseus cluster.
Dr. Lee Spitler
Title: Breakthrough Listen: jump-starting SETI research
Abstract: I'll share my recent experience sitting in on the advisory committee meeting for Breakthrough Listen - a $100 million initiative to fund SETI research over the next 10 years. This will be an informal talk about SETI, the planned Breakthrough Listen projects and opportunities for participating in the future.
Prof. Orsola De Marco
Title: “The Common Envelope Problem” - straddling the theory-observation divide
Abstract: The common envelope binary interaction happens when two stars temporarily merge into a single envelope. The resulting energetic exchange results in a merger or in a binary with short period. Phenomena such as gravitational wave emitting mergers, type Ia supernovae or any type of compact evolved binaries including evolved stars with planets must have gone through one or two common envelope phases. The physical description of this phenomenon is so complex that no predictive model exists. As a result, it remains impossible to understand the formation of compact binaries and to explain many transients that derive from binary interactions and mergers. Population models that predict the rates of phenomena such as type Ia explosions or the rate of observable gravitational waves use plausible prescriptions for the common envelope interaction, but admit to order-of-magnitude uncertainties when it comes to predicting compact binaries birthrates. I will discuss these problems in the context of the work our group has carried out in the last few years, where we have developed 3D hydrodynamic simulations of the common envelope interaction, while harvesting every possible observational constraint to use as simulation validation.
Dr. Remco van den Bosch
Title: Galaxies and their Super-Massive Black Holes
Abstract: In galaxy evolution studies, the galaxies and their central super-massive black holes are commonly linked together through bulge growth scenario's. The evidence is the tight correlation between the black hole mass and the bulge mass in early-type galaxies. Surprisingly, the total mass of the galaxy does not correlate well with black holes mass. In this talk, I will show how black hole masses are measured with stellar kinematics. And I will show how the host galaxy properties correlate to black hole mass. And finally, I will show that the bulge is not the primary correlator with BH mass. Instead it is set by the global processes of galaxy formation. As such, the local processes that grow bulges are not responsible for the bulk of black hole growth.
Prof. Tim Bedding
Title: A Golden Age of Asteroseismology with Kepler
Abstract: Stellar astrophysics has entered a new golden age, thanks to wonderfully precise measurements being returned by NASA's Kepler mission. Kepler is a 0.9-metre space telescope that has been monitoring the
brightness of more than 100,000 stars with extraordinary accuracy for more than four years. Its main goal is to discover extra-solar planets by detecting the small dips in light as they transit their parent stars. The mission has been spectacularly successful, with thousands of candidates reported. Meanwhile, Kepler's observations of oscillations in thousands of stars have led to a revolution in asteroseismology. Key results include detecting gravity modes in red giant stars and characterizing stars found to host exoplanets. Upcoming results from ESA's Gaia mission will add to the excitement, as will the launch next year of TESS, which is an all-sky follow-up mission to Kepler.
Title: In-situ IMF at z~2
Abstract: The development of sensitive Near Infra-Red instruments has made it possible to study the galaxy properties at z~2, just 3Gy after the Big Bang. This is expected to be the time period where galaxies are actively star forming and evolving rapidly to form the massive galaxies that are observed in our local neighbourhood. ZFIRE is a survey, which utilises the MOSFIRE instrument on Keck telescope over 18 nights to study properties of ZFOURGE selected mass complete galaxies in rich environments at z~2.
In my talk I will present results of the first ever attempt to constrain the Initial Mass Function (IMF) of galaxies at these redshifts using a cluster and a field sample. We have investigated the degeneracy between the star formation histories and the IMF to make strong constrains on the stellar mass distribution of these galaxies using synthetic stellar spectra. I will focus on the role of dust, star-bursts, stellar rotation, binaries, and metallicity on determining observed galaxy properties at z~2 to address whether ZFIRE results favour the canonical concept of a universal IMF.
Title: Signposts of Massive Star Formation
Abstract: Massive stars are largely responsible for the structure and evolution of galaxies. They evolve rapidly and lie deeply embedded within molecular clouds. However, their formation processes are not well known.
I am using class I methanol masers to probe proto-stellar regions in the southern sky. I have identified 15 regions with maser activity and and will demonstrate the use of masers as a tool for probing hidden proto-stellar environments.
I will discuss the physical environments of these regions, in particular how methanol masers trace shocks and outflows. I will also demonstrate how my results inform methanol maser theory.
Title: Gaps, rings and spirals in protoplanetary
Abstract:The new generation of instruments such as ALMA and VLT/SPHERE offer new spectacular views of protoplanetary discs. They reveal structures such as gaps, rings, shadows and spirals. I will show how the thermal emission and molecular maps from ALMA can be compared to scattered light images from SPHERE to provide insight on the main physical mechanisms at play in the discs. In particular, I will present a few recent results that allow us to put quantitative constraints on the evolution of dust grain and on the mechanisms of planet formation.
Title: The SUNBIRD project: Uncovering supernovae in luminous infrared galaxies
Abstract: A substantial number of core-collapse supernovae (CCSNe) are expected to be hosted by luminous infrared galaxies (LIRGs) due to the intense star formation rate of these galaxies, but very few have been found. This makes these very dusty LIRGs prominent hunting grounds to resolve the so called “Supernova Rate problem”, where up to half of the CCSNe expected from the measured cosmic star formation rate are not observed. In the SUNBIRD (Supernovae UNmasked By InfraRed Detection) project we aim to uncover dust-obscured supernovae by monitoring over 25 LIRGs, using near-infrared Laser Guide Star Adaptive Optics imaging on the Gemini South and Keck telescopes. Such discoveries are vital for determining the fraction of all supernovae which will be missed as a result of dust obscuration by current and future optical surveys. I present the first results of SUNBIRD, which includes both supernova detections very close to galactic nuclei as well as in surprisingly isolated regions of these LIRGs.
Title: An exciting new
method for finding binaries and planets
Abstract: I will present a new method for determining the orbital parameters of non-eclipsing binary stars via their oscillations. The method has now been applied to 3,500 classical pulsators, and preliminary orbital solutions are already available for more than 10 percent of them. The detected companions include planets, brown dwarfs, main sequence stars with masses between 0.1 and 2.5 Msun, and possible compact objects such as neutron stars and black holes. The method can shed light on the orbital period distribution of binary stars where traditional methods (RVs, eclipses) are not applicable. I will show that all of these methods are complementary, each detecting binaries in different parameter spaces. I will comment on the precision available and the implications for planet occurrence around A/F-type stars.
AGN obscuration and host galaxies
Abstract: With SDSS and WISE data, we study the mid-IR properties of a large sample of local Seyfert 2 galaxies. We find the host-subtracted mid-IR luminosities are linearly correlated with [OIII] luminosities for three orders of magnitude. The partition functions of the total integrated [OIII] and mid-IR luminosities from AGNs, as a function of a variety of host galaxy properties, are identical, consistent with the expectation of simple AGN unified model. However, the mid-IR emission is correlated with excessive number of neighbouring galaxies within a projected distance of 100 kpc, while [OIII] emission is not. It implies a phase of torus formation during galaxy interactions.
Title: Discovery and
Multi-wavelength Study of Planetary Nebulae in the Small Magellanic Cloud
Abstract: Planetary nebulae (PNe) represent an important but brief (~ 10,000 year) late stage of stellar evolution experienced by most low- and intermediate-mass stars. They play a crucial role in understanding various aspects of late stellar evolution, such as mass-loss and the subsequent interstellar enrichment by the products of nucleosynthesis like oxygen, nitrogen and dust. Their ionised gas shells exhibit numerous, strong emission lines that are excellent laboratories for understanding plasma physics. PNe are visible to great distances due to these strong lines that permit determination of nebula size, age and expansion velocity. Determining PNe radial velocities also allows us to trace kinematic properties of their host galaxies. I will present ten new PNe discovered in the Small Magellanic Cloud (SMC) from deep UK Schmidt telescope narrow-band H-alpha and broad-band short-red 'SR" images and confirmed spectroscopically. I will also review archived information and available imagery for previous SMC PN detections and various other types of emission objects in this galaxy, and show some preliminary results from my research.
Title: The pursuit of
determining precisely how galaxies form, transform and evolve constitutes the
most active fields in extragalactic astrophysics today.
Abstract: Clusters of galaxies are the largest and most massive virialized objects in the observable Universe, growing hierarchically over cosmic time by the accretion of surrounding gas, dust and matter, including the infall of individual field galaxies or groups of galaxies. More rarely, clusters of galaxies grow by means of a gravitational merger between two or more existing clusters of galaxies, providing the most extreme example of this hierarchical formation scenario. In order to understand the kinematic state and dynamical history of major cluster mergers, and use that advancement to understand galaxy properties and how they evolve over time, we will consider this most extreme example - a major cluster merger - as this will exemplify the physical processes governing infalling galaxies, and reveal clues as to their differing properties.
This talk focuses on the galaxy cluster Abell 2744, a massive cluster at a redshift of z = 0.3, and one of the most complicated merging systems known. Using archival Australia Telescope Compact Array (ATCA) radio continuum data of Abell 2744, I will present my preliminary results obtained during the first year of my PhD.
Title: The SAMI Galaxy
Survey: The Impact of the Cluster Environment on the Star Formation of
Abstract: It is well-known that the star-forming properties of galaxies that reside in the dense cores of galaxy clusters are remarkably different from those in the field; quiescent early-type galaxies are much more prevalent in cluster cores whereas star-forming spirals dominate in the field. These differences must be reconciled with the hierarchical nature of large-scale structure formation, where the cluster galaxy population increases by the accretion of galaxies from lower density environments. The dominant mechanism responsible for transforming infalling galaxies, whether it be due to pre-processing prior to infal or due to cluster specific mechanisms, remains elusive. Getting to the heart of this issue requires a robust definition of galaxy environment which is closely related to the physical mechanisms which may be at play, along with resolved information on the recent and ongoing star formation of the infalling galaxies. The SAMI Galaxy Survey will provide resolved spectroscopy for around 3600 galaxies. Of those galaxies, 700 have been selected to be members of eight massive clusters of galaxies. These eight clusters were the subject of a deep redshift survey using the Anglo-Australian Telescope's AAOmega multi-object spectrograph, providing a 2300 strong sample of spectroscopically confirmed cluster members that have been used to characterise the dynamical properties of each cluster (galaxy membership, cluster mass and substructure). In particular, the redshift survey has allowed a robust characterisation of the projected phase-space distribution of the clusters. The position of a galaxy in projected phase-space can be used as a proxy for the time since infall for a galaxy. In this talk, I will present an analysis of the resolved star forming properties of SAMI cluster galaxies which, based on their position in projected phase-space, are very likely to be encountering the cluster core for the first time. The majority of these galaxies show evidence for young (<1Gyr) stellar populations with no ongoing star-formation in the outer parts of the disk, indicating that star-formation has recently stopped there, while also showing ongoing star formation in their centres. This indicates the galaxies are having their star formation quenched from the outside-in, likely due to the effects of ram-pressure stripping as they traverse the clusters.