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Colloquia Series

For more information on colloquia at the Centre for Astrophysics and Supercomputing please contact Dr. Nikole Nielsen ()

Swinburne Virtual Reality Theatre
AR Building, Room 104
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2012 Colloquia


Thursday Dec 13, 11:30
Bil Dullo ()
Student Review: Bil Dullo's 30-month PhD review
Tuesday Dec 11, 11:30
Guido Moyano Loyola (Swinburne)
Student Review: Guido Moyano Loyola 18-month review
Tuesday Dec 4, 11:30
Shuvo Uddin ()
Student Review: Shuvo's PhD confirmation review
Thursday Nov 29, 11:30
Max Bernyk ()
Student Review: Max's 30 Month Review
Thursday Nov 22, 11:30
Alexander Heger (Monash)
Colloquium: Evolution, Death, and Nucleosynthesis of the First Stars
Abstract: The first generation of stars was made of material of primordial composition, almost exclusively hydrogen and helium, in contrast to later generations of stars that bear some level of "pollution" made by earlier generations of stars. This has notable impact on their evolution, starting with the way they do hydrogen burning, to how compact and how hot they are, i.e., how much and what ionizing radiation they emit, to how fast they spin, to how much mass they lose, and, finally, to what elements they synthesize in what quantities. The additional complication is our limited knowledge of the initial mass spectrum of this first generation of stars. Theoretical calculations of the formation of the first stars, however, suggest there may have been a preference for more massive stars, We use computer simulations to models the evolution of those very massive primordial stars and their final deaths as supernovae. The nucleosynthesis produces we find for those very massive primordial stars, however, does not agree with any observed abundance pattern to date. Hence an interesting question is in how far we can use abundance information we obtain from stars in our own galaxy today, preserved from the infancy of our galaxy and its building blocks, to reconstruct the properties of the first stars.
Tuesday Nov 20, 11:30
Kathrin Wolfinger ()
Student Review: 30 Month PhD Review: The effect of environment on the evolution of nearby gas-rich spiral galaxies
Abstract: The Ursa Major region is an ideal target to study the effect of environment on the evolution of gas-rich galaxies as it is nearby and most of the known member galaxies are late-type galaxies that are rich in neutral hydrogen (HI). I investigate 480 deg^2 and a heliocentric velocity range from 300-1900 km/s using data from the HI Jodrell All Sky Survey (HIJASS). The surveyed region includes the Ursa Major cluster, parts of the neighbouring Canes Venatici groups and the filamentary structure connecting it to the Virgo cluster. In this talk I will present an overview of the region: the peak-flux limited catalogue containing 166 HI sources, 10 of which are first time detections in HI including a candidate galaxy/tidal tail/HI stream and two HI detections with extended HI envelopes. Furthermore I will show preliminary results from my studies regarding substructures in the region and their dynamics to investigate if Ursa Major is an unevolved and newly forming cluster in the context of hierarchical structure formation.
Thursday Nov 15, 15:00
Romeel Dave (Arizona)
Colloquium: Galaxy Formation in the Cosmic Ecosystem
Abstract: Galaxies are born, live, and die within a cosmic environment that shapes their properties and evolution. I will discuss an emerging new scenario for galaxy evolution during their main (star-forming) growth phase. The key idea is that galaxies live in a balance between smooth, filamentary accretion from the intergalactic medium (IGM), rapid processing of gas into stars, and strong and ubiquitous galactic outflows. Using supercomputer hydrodynamic simulations, we investigate how this balance governs the stellar, gaseous, and metal content of galaxies across cosmic time. I will show comparisons of such models to a wide range of multiwavelength galaxy and IGM data, and discuss how such observations constrain the core physical processes. I will argue that solving the longstanding problem of galaxy formation in a cosmological context is tantamount to understanding the cycle of material between galaxies and their surrounding cosmic ecosystem.
Friday Nov 9, 11:30
Florent Renaud (AIM Saclay)
Colloquium: SPECIAL DATE: Galactic and stellar scales coupled: birth and death of star clusters
Abstract: Stars form in a turbulent ISM whose properties directly depend on galactic scale phenomena, like bars, spiral waves, mergers, etc. Using an AMR simulation of the Milky Way, I will present descriptions of the properties of the interstellar medium, in a fully consistent galactic context, down to the sub-parsec scale. Very fine structures like nuclear rings or interstellar filaments and their properties are analyzed to better probe the physics of star formation. For the other end of the story, the galactic scale also plays a major role in the dissolution of star clusters, through tides. Thanks to N-body simulations of star cluster embedded in arbitrarily complex tidal fields, I will describe the role of galaxy mergers in the accelerated dissolution of these objects.
Thursday Nov 8, 11:30
Rita Tojeiro (Portsmouth)
Colloquium: Using passively evolving galaxies to understand Dark Energy using BOSS
Abstract: The Baryon Oscillation Spectroscopic Survey (BOSS), part of SDSS-III, is currently in the process of obtaining spectroscopic redshifts for 1.5 million galaxies over 10,000 square degrees of sky, with a mandate to measure the expansion rate of the Universe to the 1% level. This level of precision requires not only an unprecedented dataset, but also a thorough understanding of the data, the pipeline and of the galaxy populations that are observed.

I will summarise the latest galaxy-clustering results from BOSS, with a focus on using well-understood populations of galaxies and their evolution in order to improve the measurements of the growth rate of structure, and eventually our understanding of Dark Energy.
Thursday Nov 1, 11:30
Martin Stringer (Paris Observatory)
Colloquium: Going Ballistic! How the fundamental physics of supernova winds maps onto galaxy properties
Abstract: Any viable theory of the formation and evolution of galaxies should be able to account for the mass of baryons contained, or rather not contained, in the massive collapsed regions that host galaxies. Supernova winds are now an accepted part of the explanation for this deficit, yet citations to this effect often list from a vast melee of modelling strategies and numerical simulations, rather than elegant analytic treatments of the process from the 1970s. By re-examining these classic works, and re-applying them with the hindsight of modern cosmology, I will show that these theories seem to have successfully predicted the connection between between baryon content and galaxy circular velocity that we now find in recent observational surveys. So do our sophisticated simulations simply corroborate the traditional assumptions that were applied? Or are we all arriving at the right answer, but for the wrong
reasons..?
Tuesday Oct 30, 11:45
Andrew Walsh (James Cook University)
Colloquium: SPECIAL DATE & TIME: Colloquium - HOPS and MALT: Star formation in the Inner Galaxy
Abstract: I will report on some of the surprising discoveries made with HOPS (the H2O southern Galactic Plane Survey), including a possible precursor to a super star cluster and the lack of ongoing star formation in the Central Molecular Zone that is located within a few hundred parsecs of the Centre of our Galaxy. I will also introduce the first results of the main MALT-45 survey, which is targeting dense gas, traced by CS, SiO and methanol, and SiO and methanol masers in the Galaxy. This survey is the first of its kind to search for Class I methanol masers in an untargeted way, using autocorrelation data from the ATCA.
Thursday Oct 25, 11:30
Richard de Grijs (Peking University)
Colloquium: Star cluster formation and early evolution: the big picture
Abstract: What has been the most profound discovery, progress or idea that has emerged in astronomy over the last decade? And what will be the most important challenge in astronomical research in the next decade? These questions are at the heart of our discipline, but we rarely venture outside of our own niche areas. I will attempt to focus on the broad picture underlying the field of star formation and discuss the requisite conditions for sustained progress in this field, aided by recent achievements in the context of my group's star cluster research.
Tuesday Oct 16, 11:30
Giorgos Vernardos (Swinburne)
Student Review: Giorgos Vernardos 18-month PhD Review
18-month PhD Review Talk
Tuesday Oct 9, 14:30
Ed Hinds (Centre for Cold Matter, Imperial College, London)
Colloquium: SOLL Seminar: Is the Electron Round: the Search for the Electron's Electric Dipole Moment
Monday Oct 8, 14:00
Paola Oliva (Swinburne)
Student Review: Paola Oliva 6-month review
Thursday Oct 4, 14:00
Roger Davies (Oxford)
Colloquium: Towards a new paradigm for early type galaxies
Abstract: In this talk I will propose a re-evaluation of our view of early type galaxies (ETGs) based on the results of recent integral field surveys of local galaxies. These have revealed a dichotomy of properties depending on the specific angular momentum of a galaxy. ETGs with low specific angular momentum are found to be rarer than previously thought. They are distinct galaxy population with a different intrinsic shape distribution, mass-to-light ratio, ionised gas properties, and age. I will summarise the results from the volume limited survey of 260 ETGs, ATLAS-3D, which gives us a representative view of the local Universe, propose a revision to Hubble's Tuning Fork Diagram to reflect the new view, and discuss the physical processes that shape galaxies.
Tuesday Oct 2, 11:30
Sreeja Kartha (Swinburne)
Student Review: Sreeja Kartha 18-month review
Thursday Sep 27, 11:30
Vincenzo Pota ()
Student Review: 30 mth review for Vincenzo Pota
Wednesday Sep 26, 15:00
Antonio Limosani (Melbourne)
Colloquium: Has the Higgs Boson been discovered at the CERN Large Hadron Collider?
Abstract: On July 4, 2012, based on preliminary data analyses both the ATLAS and CMS collaborations announced the discovery of a new fundamental particle that is consistent with the long sought after Higgs Boson. I will discuss the important role the Higgs Boson plays in the standard model of Particle Physics and present the latest search results of the ATLAS collaboration. I will also discuss the next steps in elucidating the particle's true nature. Is it the Higgs Boson predicted by the standard model? Or is it a manifestation of something more exotic?
Tuesday Sep 25, 11:30
Paul Coster ()
Student Review: Paul Coster's 18-month PhD review
Thursday Sep 20, 11:30
Chris Usher ()
Student Review: 30 mth review for Chris Usher
Thursday Sep 20, 14:30
Kat Barger (Wisconsin)
Colloquium: Warm, Ionized Gas Revealed in the Magellanic Bridge Tidal Remnant: Characterizing the Baryons and the Escaping Ionizing Photons
Abstract: Galaxy interactions have greatly disturbed and redistributed the gas in the Magellanic System throughout the halos of the Milky Way and the Magellanic Clouds. In this talk, we will discuss the results of the highest sensitivity and kinematically resolved emission-line survey of the warm (10^4 K) ionized gas of the Magellanic Bridge using the Wisconsin Hα Mapper. This census allows us to investigate the baryon content, properties of the gas, source of the ionization, and fate of this tidal remnant. The Hα detections across the entire Magellanic Bridge enables us to place constraints on the fraction of ionizing photons that escape from these galaxies; this is an important parameter for determining the influence that dwarf galaxies had during the epoch of reionization and the contribution of ionizing photons they currently supply to the extragalactic background. The [SII] and [NII] observations allow us to further understand the state of the gas and the source of the ionization. Determining the properties of tidal debris is key for understanding the evolution of these galaxies and other tidally disturbed systems.
Tuesday Sep 18, 11:30
Helga Denes ()
Student Review: Helga Denes 18 month review
Friday Sep 14, 11:30
Dennis Zaritsky (Arizona)
Colloquium: SPECIAL DATE: Evidence for Two Distinct Stellar Initial Mass Functions
Abstract: On the basis of new observations that track the mass-to-light ratios of stellar clusters in the Local Group vs. age, we find that no single population model fits the entire population. Specifically, the data suggest that younger clusters (< few Gyr old) tend to favor a more bottom-heavy IMF and older clusters favor a less bottom-heavy IMF. Alternate interpretations will be discussed, but they are appear unlikely to explain the observations.
Thursday Sep 13, 11:30
Christopher Conselice (Nottingham)
Colloquium: The History of Galaxy Formation as seen with the Hubble Space Telescope
Abstract: I will present an analysis of the modes of galaxy formation for massive galaxies with log M_star > 10 at z < 3 based on data from the Hubble GOODS NICMOS and CANDELS Surveys. I will discuss the role of major mergers, star formation, AGN feedback, and for the first time, minor mergers, in the formation of massive galaxies down to z = 0. This is possible due to using new near-infrared Hubble Space Telescope imaging from NICMOS and WFC3 focused on massive galaxies in the distant universe. I will further show that modes besides the above are needed to form galaxies and will argue that gas accretion from the intergalactic medium is an important method for adding mass to the most massive galaxies, and potentially a major new part of the galaxy formation process. I will conclude with a discussion of new results and future work needed in this area.
Thursday Sep 6, 11:30
Roberto Gonzalez (Chicago)
Colloquium: Satellites in MW-like hosts: Environment dependence and close pairs
Abstract: Following the method in Busha et al 2011. where they estimate the MW host mass likelihood based on the statistics of halos hosting satellites similar to the Magellanic clouds(MCs), I explore how this estimate change in the Local Group(LG), where LG analogous are selected in the Bolshoi simulation by the presence of a M31-like halo partner, distance to
Virgo-like cluster, and environment constraints. I also explored the sensitivity of additional MCs constraints, finding that ~1% MW-mass halos live in LG-like systems, and show a satellite velocity distribution shifted to somewhat higher values, although the difference is not large.
Tuesday Sep 4, 11:30
Rob Bassett ()
Student Review: 6 month PhD student review - Rob Bassett
Thursday Aug 30, 11:30
Chris Brook (Madrid)
Colloquium: A (biased) view of the state of galaxy formation simulations, and what they can tell us
Abstract: Cosmological simulations of galaxy formation have made progress in the last decade, yet problems remain with numerics and with input physics, and different groups seem to get wildly different results, as was demonstrated in the recent Aquila comparison project.
I will present galaxies with a wide range in mass from our MaGICC- Making Galaxies in a Cosmological Context- program that match observed relations between halo mass, stellar mass, luminosity, rotation velocity, size, colour, star formation rate, HI mass, baryonic mass and metallicity. I will explain why our galaxies succeed where others fail, and point to remaining degeneracies in our model. I will then present interpretations of dynamics and chemical evolution of disc galaxies that have been guided by analysis of our simulations.
Thursday Aug 16, 11:30
Pierluigi Cerulo (Swinburne)
Student Review: Pierluigi's 18 month PhD review
Thursday Aug 9, 11:30
Stas Shabala (University of Tasmania)
Colloquium: AGN in galaxies: where do they come from, and what do they do?
Abstract: Feedback from Active Galactic Nuclei (AGN) is a key mechanism regulating the formation and evolution of galaxies. It is thus important to understand how the AGN are triggered, and how they interact with galaxies. I will argue that it is particularly important to be able to do two things: 1) measure the kinetic power of AGN jets; and 2) sequence the co-triggering of star formation and AGN activity.

I will use multi-wavelength (radio + optical) data to show that powerful AGN can do feedback on much larger scales than their weak counterparts, providing a qualitatively different mode of feedback. I will also show that radio AGN observations, together with star formation histories, can facilitate measurements of the time delay between the onset of star formation and AGN activity.
Thursday Aug 2, 11:30
Gonzalo Diaz (Swinburne)
Student Review: 30-month PhD review
Tuesday Jul 31, 11:30
Luca Cortese ()
Colloquium: The Herschel Reference Survey: Gas, Dust, Star formation and Metals in the local Universe.
Multi-wavelength surveys are finally providing a census of all the baryonic components of galaxies (gas, stars, metals, dust, etc.), making it possible to start building a coherent picture of the star formation cycle in galaxies.

In this talk, I will introduce one of such endeavors, the Herschel Reference Survey (HRS), a Herschel/SPIRE Guaranteed time program focused on the study of the star formation cycle in a volume-, magnitude-limited sample of nearby galaxies in different environments. I will give an overview of some of the key results from the HRS, obtained by combining the Herschel observations with a multiwavelength dataset covering the ultraviolet to the radio regime. Particular attention will be given to the characterization of the statistical properties of cold gas, dust and metals in nearby galaxies and to the effect of the environment on the various steps of the star formation cycle. The HRS will be an important benchmark for studies of high redshift galaxies, as well as a useful reference for theoretical studies.
Thursday Jul 26, 11:30
Andrew Cumming (McGill)
Colloquium: New Constraints on Neutron Stars from Cooling Transients
Abstract: Many years of theoretical work have given us a detailed picture of neutron star interiors. In this talk I will show that recent observations of cooling neutron stars on timescales of days to years offer us the most detailed observational constraints yet on the theory. I will describe calculations of the thermal relaxation of neutron stars after transient heating events and show that they naturally explain the observed outbursts, constraining the physical processes inside the star. I will discuss both accreting neutron stars, for which the observed cooling times constrain the transport properties, composition, and structure of the neutron star crust, and magnetars, for which cooling following transient outbursts is revealing where magnetic field decay deposits energy inside the star.
Thursday Jul 19, 11:30
Jade Carter-Bond (UNSW)
Colloquium: Extrasolar Terrestrial Planets: How common is Earth?
Abstract: The details of the formation of terrestrial planets are long-standing questions in the geological, planetary and astronomical sciences, with the discovery of extrasolar planetary systems placing even greater emphasis on these questions. Further compounding this issue is the fact that host stars display enrichments in several key planet-forming elements. To date, very little has been done on combining detailed chemical abundance and distribution models with specific planetary formation simulations. I will discuss simulations of the bulk compositions of the terrestrial planets in a variety of extrasolar planetary systems. Terrestrial planets produced vary in composition from those resembling the planetary composition of the Solar System to being enriched in Ca and Al, Fe or biogenic species such as O, P and C. These enrichments can be taken to the extreme to produce planets unlike anything previously observed. Similarly, migration of the giant planets significantly alters the composition of the final terrestrial planet by redistributing material throughout the system.
Tuesday Jul 17, 11:30
Michael Childress (ANU)
Colloquium: SPECIAL DATE: Environments and Progenitors of Type Ia Supernovae
Abstract: Type Ia Supernovae (SNe Ia) are excellent standardizable candles which
can be used to map out the expansion history of the Universe and
measure the properties of Dark Energy. Recent studies showed that SN
Ia luminosities corrected using the current standardization methods
exhibit a residual bias with respect to the properties of their host
galaxies. I will present a sample of SNe Ia and their host galaxies
from the Nearby Supernova Factory and show that our data support and
strengthen these results. Furthermore, I will explore several
astrophysical effects which may be driving this observed trend,
including the variation of stellar ages, metallicities, and
inter-stellar dust content along the galaxy mass sequence.

I will then report on the status of the SkyMapper Transients survey,
including plans for followup observations of SNe and their
environments using the Wide Field Spectrograph (WiFeS). I will briefly
present the new WiFeS Python data reduction pipeline which will enable
rapid classification of new SkyMapper transients, as well as other
astrophysical studies conducted by the WiFeS user community.
Tuesday Jul 10, 11:30
Signe Riemer-Sorensen (Queensland)
Colloquium: SPECIAL DATE: The smallest particles and the largest scales - neutrino mass constraints from cosmology
Abstract: Despite being the smallest experimentally observed particles, the neutrinos provide one of the greatest challenges for modern physics. The Standard Model of particle physics describes them as being exactly mass-less. Nonetheless, neutrino oscillation experiments provides precise measurements of their mass differences, but not the overall mass scale. Massive neutrinos have a significant effect on the structure formation history of the Universe. The neutrinos are relativistic in the early Universe where they free stream out of overdensities, thus spreading out the gravitational potential and damping the growth of structure, which can be observed in the galaxy distribution today. I will present new results on the neutrino mass
derived from large-scale structure in the three-dimensional galaxy map provided by the Australian WiggleZ Dark Energy Survey, which currently provide the strongest robust neutrino constraints from galaxy surveys.
Thursday Jun 28, 11:30
Sean Farrell (Sydney)
Colloquium: Bridging the Gap Between Stellar Mass and Supermassive Black Holes
Ultraluminous X-ray sources (ULXs) are extragalactic objects that are located outside the nuclei of their host galaxies with luminosities that exceed the Eddington limit for a stellar mass black hole. These luminosities have been interpreted as evidence of a new class of intermediate mass black holes with masses between ~100 – 100,000 Msun. The brightest of these objects – the “hyperluminous” X-ray sources – have luminosities above 1E41 erg/s that cannot be easily explained without intermediate mass black holes. However, the luminosities of the bulk of ULXs could be explained through a combination of mild super-Eddington accretion and beaming. Here I will describe the multi-wavelength observing campaign targeting ESO 243-49 HLX-1, the most luminous ULX currently known and the strongest candidate intermediate mass black hole. I will also present the results of a recent study into transient behaviour in ULXs that shows that the bulk of the population cannot be explained via hyper-accretion onto stellar mass black holes with masses between ~10 – 30 Msun.
Thursday Jun 21, 11:30
James Jackson (Boston University)
Colloquium: High-Mass Star Formation in Filamentary Infrared Dark Clouds

Abstract: Although low-mass star formation is well understood, the earliest stages of high-mass star formation has remained elusive. Work by our group and others now shows that high-mass stars are born in infrared dark clouds (IRDCs). IRDCs are identified as regions of large extinction in mid-infrared images of the Galactic plane. We have cataloged ~10,000 IRDC candidates from the Midcourse Space Experiment 8 micron survey of the Galactic plane and determined their kinematic distances from molecular line observations. IRDCs have characteristic sizes of ~few pc and masses of ~1000 M_sun or more, and are located primarily in spiral arms. Submillimetre and millimetre continuum observations reveal that they contain dense cores with masses ~100 M_sun and sizes <0.5 pc. Many of these cores show unambiguous signs of high-mass star formation, including high velocity outflows, shocks, and luminous embedded sources. It is probable that all high-mass stars and star clusters originate in IRDCs. I discuss one remarkable filamentary IRDC, the "Nessie nebula," with an aspect ratio of over 300:1. The cores in Nessie show a roughly periodic spacing of ~5 pc. This periodicity suggests that a fluid instability called the "sausage" or "varicose" instability is important. The large numbers of filamentary IRDCs, along with the evidence that they are the sites of high-mass star formation, suggest that the "sausage" instability in filamentary IRDCs is a natural mechanism to form molecular clumps with the characteristic sizes and masses of star clusters.
Thursday Jun 14, 11:30
Brad Gibson (Central Lancashire)
Colloquium: Spirals with Supercomputers: Have We Finally Got it Right?
Abstract: The history of disk galaxy simulation is dotted with remarkable successes, tempered by frustrating impasses, including an inability to recover anything remotely similar to the Milky Way. Recent advances suggest that we might have made a breakthrough by generating essentially bulgeless disks. I will examine the evidence for this new-found optimism and identify where the shortcomings suggest we should be concentrating our future efforts.
Thursday Jun 7, 11:30
Sarah Buchner (Hartebeesthoek Radio Astronomy Observatory)
Colloquium: HartRAO Monitoring of glitches in the Vela Pulsar
Abstract: The Vela pulsar, like many other young pulsars, undergoes occasional sudden ''spin-ups'' in rotational frequency known as glitches. These glitches are characterized by a sudden (less than 30s) rise in the rotation frequency accompanied by a jump in the spin-down of the pulsar. This is generally followed by rapidly decaying transients in the spin-down and a gradual linear recovery. This recovery provides insight into the internal structure of the neutron star. The 26m telescope at HartRAO, 60 km North west of Johannesburg, South Africa was been used to monitor the Vela pulsar almost daily from 1985 in order to monitor these glitches. I will discuss these observations and the glitch monitoring system. During the entire monitoring campaign 10 large glitches have been observed. The majority of the glitches show a similar recovery pattern. I will discuss this pattern and the exceptions to it.
Wednesday May 30, 11:30
Boris Haeussler (University of Nottingham)
Colloquium: SPECIAL DATE - MegaMorph: automated profile fitting in multi-band surveys
Abstract: Most galaxies are fundamentally multi-component systems, comprising a spheroidal bulge and a thin disk. As these components have largely independent origins, separating them provides important information to constrain models of galaxy formation and evolution. Current methods are not sufficiently developed for routine use of this technique on large samples of galaxies. I will introduce the MegaMorph project, in which we develop an accurate, robust tool for measuring the key physical quantities of the individual structural components of galaxies imaged by large multi-band surveys, e.g. GAMA. The focus of our work is the extension of current tried-and-tested galaxy fitting/decomposition techniques (e.g. GALAPAGOS& GALFIT) to fully utilise multi-band imaging, as routinely produced by modern surveys, both ground- and space-based. Using all the available multi-colour information in the galaxy fitting process enables much more robust decompositions in terms of physically-meaningful parameters.
Tuesday May 29, 14:30
Nicola Pastorello ()
Student Review: Nicola Pastorello 6-month review
Thursday May 17, 11:00
Brian Boyle (CSIRO)
Colloquium: The Australian SKA Pathfinder: Progress Report.
NOTE SPECIAL TIME 11AM - Abstract: I describe the latest developments with the construction of ASKAP and the Murchison Radioastronomy Observatory. I will also provide an overview of some of the ASKAP survey science programs.
Tuesday May 15, 11:30
Bernard F Whiting (Florida)
Colloquium: Stochastic gravitational wave background results from LIGO
NOTE SPECIAL DATE TUE 15/05. Abstract: Theories which describe the physics of the early Universe frequently include scenarios for the production of gravitational waves. For cosmic superstring models, gravitational waves which survive to the current epoch would have resulted from the superposition of a large number of unresolved sources while, more generically, gravitational wave production might be related to the equation of state characterizing matter and energy in the very early Universe. Whatever cosmic physics model is actually responsible for creating a stochastic background of gravitational waves, we can expect its unique imprint to be evident today, just as the thermal history of the early Universe has imposed a unique black body temperature, and a precise fluctuation spectrum, on the cosmic microwave background (CMB). Direct measurement of the amplitude of a stochastic GW background is therefore of fundamental importance for understanding the evolution of the Universe during its earliest moments, when it was undergoing processes which are inaccessible to more standard astrophysical observations. I report on recently published limits on the amplitude of the stochastic gravitational-wave background, using the data from a two-year science run of the Laser Interferometer Gravitational-wave Observatory (LIGO). The result constrains the energy density of the stochastic gravitational-wave background normalized by the critical energy density of the Universe, in the frequency band around 100Hz, to be less than 6.9x10^-6 at 95% confidence. Impact on several models for the early Universe is discussed.
Thursday May 10, 11:30
Juan Madrid (Swinburne)
Student Review: Ph.D. 30-month review: Structural Parameters of Compact Stellar Systems
Most extragalactic star clusters have a scale size narrowly centered around three parsecs, similar to their Galactic counterparts. In the last decade, however, a rush of discovery of new stellar systems, brighter,larger, and more massive than "standard" globular clusters has taken
place. The scale sizes of globular clusters, extended star clusters and ultra-compact dwarfs in the Coma cluster, and the fossil group NGC 1132 will be presented. The results of N-Body simulations helps us to understand the physical mechanisms that determine the scale-sizes of
star clusters and compact stellar systems in general.
Thursday May 3, 11:30
Christopher Stockdale (Marquette, AAO)
Colloquium: Radio Supernovae: CSI – Circum-Stellar Investigations
Core collapse supernova events play a critical role in the chemical enrichment of our Universe and produce many of the critical elements needed for life to form on other planets. The stars that produce these events comprise less than a tenth of one percent of star in a typical galaxy and have lifetimes shorter than ten million years, making them very rare events in a galaxy like our Milky Way. To explore the evolution of these massive stars and how they play a role in forming new stars, we must look beyond our own galaxy, typically 10-100 million light years away. At these distances, it is practically impossible to predict which stars which explode until they have already done so. However, after the explosion, there is sometimes radio and X-ray emission produced as the supernova blast wave over runs the stellar winds shed by the star in the thousands of years prior to its death. I will present a summary of how astronomers at the Australian Telescope Compact Array and the Very Large Array use this radio emission to constrain and determine the pre-explosion evolution and environment of these massive supernova progenitor stars, as young as a few months and as old as seventy-five years after the supernova explosion.
Thursday Apr 26, 11:30
Rob Thacker (St. Mary's University)
Colloquium: Skeletons in the AGN modelling cupboard
Despite a lack of comprehensive observational support, AGN feedback has become a key component of modern theories of galaxy formation. Much of this development is due to theoretical insight gained from simulations of galaxy formation that include both star formation and AGN feedback. Yet while feedback from star formation is moderately well understood, AGN feedback is not. There are uncertainties in the physics (how does accretion actually occur? What is the duty cycle and intermittency of feedback?) and also uncertainties in how it should be implemented numerically. In this talk I will present results from an ongoing project to compare and contrast different approaches to modelling AGN feedback. I'll highlight where the greatest uncertainties are (e.g. is it black hole tracking, or modelling the accretion?) and what the prospects are for addressing some of these issues.
Thursday Apr 19, 11:30
Andrew Prentice (Monash)
Colloquium: Origin of our Solar system: new insights gleaned from MESSENGER and Cassini-Huygens missions
Abstract: Today, the Cassini-Huygens Mission to Saturn and Titan is slowly unravelling the mysteries of Saturn and its remarkable satellite system. Saturn’s largest satellite Titan is more like a planet than a moon. Its mass is nearly 60 times larger than that of the second largest moon Saturnian Rhea and its physical size exceeds that of Mercury. Titan is also unique because of its thick atmosphere which is 4 times denser than that of the Earth at its surface.
In this talk I discuss the formation of the planetary system and the satellite system of Saturn within the context of the ‘Modern Laplacian Theory’ of solar system origin. According to this model, the planets condensed form an orbiting family of gas rings that had been shed by the gravitationally contracting proto-solar cloud, some 4.6 billion years ago.
Thursday Apr 12, 11:30
Bon-Chul Koo (Seoul National University)
Colloquium: Young Supernova Remnants and Their Environments
Young core-collapse supernova remnants (SNRs) interact with circumstellar medium that the progenitors injected during their final stages of evolution. As such they provide invaluable opportunity to investigate the final moment of massive stars as well as the explosion
itself. In this talk, I will first discuss how the morphology and physical characteristics of young core-collapse SNRs are determined by the mass-loss history of progenitors. Then I will introduce three young SNRs, i.e., G11.2-0.3, G54.1+0.3, and MSH 15-52, which are thought to be the remnants of SN IIL/b (or IIn), IIP, and Ib/c, respectively. These three SNRs illustrate how diverse the environments of young SNRs are, and, on each of them, recent observations from ground-based near-infrared observatories and space-infrared telescopes revealed interesting results.
Thursday Apr 5, 11:30
Aris Karastergiu ()
Colloquium: Radio pulsars as astrophysical transients
In this talk I will describe some of the basic measurables of radio pulsars and how they have led to discovery of transient phenomena on timescales from milliseconds to decades. Long term variability has implications on our ability to precisely model the rotational properties of pulsars and the physical phenomena occurring at the pulsar. On the shortest time scales, discovery of radio transients has the potential to reveal new pulsar populations, as well as provide new
means to study supernovae and GRBs. In this context, I will present a fast transient detection system developed for LOFAR, after briefly introducing this new telescope and its early science achievements in pulsar and fast transient astrophysics.
Thursday Mar 29, 11:30
Ue-Li Pen (CITA)
Colloquium: Beating Cosmic Variance with Cosmic Tides
Abstract: We apply CMB lensing techniques to large scale structure and solve for the 3-D cosmic tidal field. We use small scale filamentary structures to solve for the large scale tidal shear and gravitational potential. By comparing this to the redshift space density field, one can measure the gravitational growth factor on large scales without cosmic variance. This potentially enables accurate measurements of neutrino masses.
Thursday Mar 22, 11:30
Jean Brodie (UCO/Lick Observatory)
Colloquium: Globular Clusters and Halo Stars: Chemodynamical Tracers of Galaxy Formation beyond the Local Group
I will discuss the new paradigm for the assembly of galaxies and their globular cluster (GC) systems emerging from recent theoretical work and supported by our imaging and spectroscopic data from the SLUGGS and SMEAGOL surveys of GCs and starlight out to many effective radii in nearby early type galaxies. Data obtained with Suprime-Cam on Subaru and DEIMOS on Keck are compared to a variety of simulations of galaxy build-up. Kinematic signatures, as well as metallicity and surface density distributions of the GCs and the underlying galaxy starlight support and constrain two-phase galaxy formation scenarios. Early "in situ" formation and subsequent minor mergers may be the dominant mechanisms for building galaxies and their GC systems. Later major mergers may have been important only in a small minority of cases. I will also explore the relationships between compact stellar systems, including a newly discovered class of faint ultra compact dwarfs (UCDs) that may be markers of the halo assembly process.
Tuesday Mar 20, 11:30
Genevieve Shattow ()
Student Review: Genevieve Shattow's 6 Month Review
Thursday Mar 15, 11:30
Ralf Kotulla (Wisconsin)
Colloquium: The connection between Lyman-alpha emission from Lyman Break Galaxies and the properties of the underlying galaxy
Lyman Break Galaxies (LBGs), easily found at higher redshifts due to the sharp drop in their spectral energy distribution shortwards of Lyman-alpha, are commonly observed and studied at almost all redshifts from z=0.3 out to the highest redshifts. LBGs with Ly-alpha emission (LAEs) are of particular interest as they allow to derive accurate spectroscopic redshifts, and as a result of that essentially all galaxies with spectroscopic redshifts z>3 (where strong rest-frame optical emission lines are shifted into the near-to-mid infrared and hence hard to observe from the ground) are also LBGs. However, the underlying processes that governs the strength of Ly-alpha is still under debate, as Ly-alpha is readily absorbed and scattered by even minute amounts of hydrogen within and around galaxies. Understanding the escape mechanism for Ly-alpha therefore offers insights into the physical conditions within and around the respective galaxies.Here we use a large sample of restframe UV spectra of ~1000 LBGs at redshifts z=1.5-3 to investigate the connection between Ly-alpha emission and the properties of their host galaxies and the evolution of these trends with redshift from z=2 to z=3. We find that LAEs are, on average, have smaller star formation rates, older ages, and less dust reddening then their LBG counterparts without Ly-alpha emission. Comparing the observed Ly-alpha luminosity to the Ly-alpha luminosity expected from their UV-derived star formation rate we find a dust-corrected escape fraction of the order of 10% independent of redshift.
Thursday Mar 8, 15:00
Tyler Evans (Swinburne)
Student Review: Tyler Evans' 18-month review
Tuesday Mar 6, 11:30
Elisa Boera (Swinburne)
Student Review: Elisa Boera's 6-month review
Thursday Mar 1, 11:30
Anna Sippel (Swinburne)
Student Review: Anna Sippel - 18 month review
Tuesday Feb 28, 11:30
Simon Mutch ()
Student Review: Simon Mutch's 30 Month Review
Friday Feb 24, 11:30
Michael Burton (UNSW)
Colloquium: Unveiling the Central Molecular Zone with Mopra
The Central Molecular Zone (CMZ) contains the richest molecular environment of our Galaxy. Spread over the central ~450x150 parsecs of the Galaxy is found ~50 million solar masses of molecular material. This environment is denser, warmer and more turbulent than that found in the giant molecular clouds of the Galaxy's spiral arms. Surprisingly, the CMZ is also a rich source of organic molecules, and these are found widely distributed across it, and not just confined to the densest cores as they are in GMCs. Until recently we have lacked the ability to examine closely this organic repository at the centre of our Galaxy. Now, with the 22m Mopra millimetre-wave telescope in Australia, we have undertaken a multiple molecular line survey of the CMZ, mapping simultaneously the distribution and dynamics of 18 molecular lines, emitting from 85-93 GHz, across a 2.5°x0.5° region of the CMZ. This work complements the continuum view from radio, infrared, x-ray and gamma- rays of this exotic and multi-facetted environment. We report on the view that is now emerging of the CMZ, our closest galactic nucleus and the only one we can resolve in detail.
Thursday Feb 23, 14:30
Nikhil Padmanabhan (Yale)
Colloquium: A 2% Distance Measurement to z=0.35
I will present recent results using the baryon acoustic oscillation (BAO) signal in the Sloan Digital Sky Survey (SDSS) DR7 sample. I will discuss the first application of the idea of density-field reconstruction to the BAO signal. Given these measurements, I will then describe how we robustly derive distance constraints from the galaxy correlation function. Applying these methods to the DR7 data yields a 2% distance measurement to z=0.35, a factor of 1.8 improvement over the unreconstructed case. I will finally discuss the cosmological implications of these measurements and then conclude with the outlook for future surveys.
Thursday Feb 23, 11:30
Catarina Ubach ()
Student Review: Catarina Ubach 30-month review
Friday Feb 17, 11:30
Michael Hudson (Waterloo)
Colloquium: SPECIAL SEMINAR: The Death of Red Galaxies: Clues from the Fossil Record
Abstract: One of the biggest puzzles in galaxy formation is not why galaxies form stars, but rather why some of them do not. I will review results from analysis of the spectra of low-redshift red galaxies (including data ultra-deep spectra in the Coma Cluster) which reveal where, when and how quickly these galaxies died. In particular, by comparing results with orbital data from N-body simulations, we disentangle internal from environmental effects.
Thursday Feb 16, 11:30
Michael Shara (American Museum of Natural History)
Colloquium: Novae, Dwarf Novae and type Ia Supernovae: How are they Related?
Abstract: Cataclysmic Variables (CVs) are usually defined to be white dwarfs (WD) accreting matter from a Roche-lobe filling companion. Accretion disk instabilities in CVs lead to dwarf nova eruptions. The 25-year old hibernation scenario of cataclysmic binary evolution posits that all dwarf novae must eventually erupt as thermonuclear runaway classical novae; and that classical novae eventually revert to being dwarf novae and then "hibernating" CVs. Recent observations provide some spectacular confirmations of the theory. One of the leading candidates for SNIa progenitors has been a special type of CV: the recurrent nova. Just published HST images are an acid test for the model, and convincingly resolve the nature of SNIa progenitors.
Tuesday Feb 14, 11:30
Francisco Pignatale ()
Student Review: Francisco Pignatale 30-month review
Thursday Feb 2, 11:30
Leonardo Testi (ESO)
Colloquium: The disks of dawn: setting the stage for the formation of planetary systems and ALMA
Abstract: Circumstellar disks appear in the early phases of formation of stars and play a key role in the assembly of the final mass of the central star and in the possible formation of a planetary system around it. I will review our understanding of the properties and evolution of disks around young stellar objects, focusing on the solids (dust and pebbles) in disk. The evolution of the solids is directly related to the initial stages of planets formation as grains are expected to grow to large pebbles and form planetesimals and rocky cores of planets. I will discuss the current observational evidence for grain evolution in disks, the difficulties and
success of theoretical models to explain observations and the latest ideas on grain populations segregation in disks. I will discuss future observational tests, in particular with ALMA Early Science and beyond, that will allow us to impose tighter constraints on models of solids evolution in disks.
I will also present the status and future development of ALMA. In particular I will give an update on Science Verification, Early Science and the expectations for Cycle 1 and the timeline for full science operations and beyond.
Wednesday Jan 25, 15:00
Jean-Pierre Macquart (Curtin University)
Colloquium: Turbulence, Transients and Telescope Design
This will be followed by a discussion on PanSTARRS