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Colloquia Series

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

Swinburne Virtual Reality Theatre
Applied Science Building, Room 406
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2002 Colloquia

Dec. 5 @ 16:00
Tamara Davis (UNSW)
Title: The Point of No Return: Understanding Event Horizons in an Expanding Universe
The event horizons of black holes have sparked the imagination of many a physicist (and many a science fiction writer). Event horizons mark a point of no return - a gravity trap from which not even light can escape. In this talk I will examine, not the event horizons of black holes, but the event horizon of the Universe itself. Black hole thermodynamics is well established and it is now generally accepted that black holes possess an entropy in proportion to their event horizon area. I will report on recent work, done in collaboration with Paul Davies and Charley Lineweaver, investigating the entropic worth of cosmological event horizons. I will also briefly discuss the recent controversy over whether black hole thermodynamics can constrain varying constants.
Nov. 7 @ 16:00
Gary Da Costa (ANU)
Title: The Star Formation History of Dwarf Galaxies
Oct. 31 @ 16:00
Ken Freeman (ANU)
Title: Near-Field Cosmology
Detailed studies of the Galaxy lie at the core of understanding the complex processes involved in baryon dissipation and galaxy formation in the early universe. I will discuss some of the dynamical and chemical signatures of galaxy formation, and describe how one might go about unravelling the dissipation of the Galactic disk.
Oct. 24 @ 16:00
Alison Ford (Monash)
Title: Abundances in Solar-type Stars
Knowing the compositions of stars is one of the keys to understanding their structures, how they form and evolve. For many main-sequence stars the only abundance which is well known is that of iron. Other metal abundances are believed to scale in the same way as iron does, but the validity of this assumption is unclear. Studies of a range of elements, including lithium, which has its own special place in astrophysics, can provide a wealth of information on stars like the Sun.
Sep. 24 @ 16:00
Burkhard Fuchs (Heidelberg)
Title: Dim Matter in the Disks of Low Surface Brightness Galaxies
An attempt is made to set constraints on the otherwise ambiguous decomposition of the rotation curves of low surface brightness galaxies into contributions due to the various components of the galaxies. For this purpose galaxies are selected which show clear spiral structure. Arguments of density wave theory of galactic spiral arms are then used to estimate the masses of the galactic disks. These estimates seem to indicate that the disks of low surface brightness galaxies might be much more massive than currently thought. This unexpected result contradicts stellar population synthesis models. This would also mean that low surface brightness galaxies are not dominated by dark matter in their inner parts.
Sep. 19 @ 16:00
Joerg Fischera (ANU)
Title: Properties of the Dust in the Circumstellar Medium of SN1987A
Measurements taken with ISOCAM on board ISO (infrared space observatory) 11 years after outburst have revealed SN 1987A as a mid-infrared (MIR) source. It will be shown that the emission is most probably from collisionally heated dust embedded in shock gas downstream of the blast wave. The dust-to-gas ratio is found to be 0.01%, an order of magnitude lower than estimates for dust abundances in the winds of red supergiant stars in the LMC. This low dust abundance can be accounted for by a combination of evaporation through the UV-flash from the supernova outburst and subsequent sputtering in the shocked gas. For this explanation to hold, dust in the pre-supernova circumstellar medium would have to have been predominantly composed of grains other than graphite, with a maximum size smaller than 0.1 micron.
Jul. 26 @ 11:00
Russ Taylor (Calgary)
Title: The Square Kilometre Array
Over the past several years an international effort has developed to solve the technical challenges required to construct a giant radio telescope with a collecting area of one square kilometre. The Square Kilometre Array (SKA) will have a hundred times more collecting area than our most powerful existing radio arrays. With spatial resolution better than the NGST, a field of view larger than the full moon and the ability to simultaneously image a wide range of red shifts, the SKA will be the worlds premier spectroscopic imaging telescope. The SKA will be able to detect the emission from atomic and molecular gas at extreme redshifts, allowing study of the "Dark Ages" of the Universe, before, and during, the transition phase when the first stars formed and reionization occurred. The wavelength range of the SKA spans the transition from emission dominated by non-thermal processes at long wavelengths and thermal radiation processes at the short wavelengths. Measurements of the atomic hydrogen and continuum emission will trace the star formation history of the Universe from the primordial galaxies to the present. In our own Galaxy, star formation processes and phenomena in the gaseous interstellar medium will be studied down to a scales of A.U.
Jul. 22 @ 16:00
Ray Jayawardhana (Berkeley)
Title: Probing the Origins of Planetary Systems
Jul. 19 @ 16:00
Rogier Windhorst (Arizona State)
Title: An HST Mid-UV Survey of Nearby Galaxies: Tools to Understand High-Redshift Galaxy Morphology
Faint and distant galaxies observed in deep CCD images are primarily seen in their rest-frame mid-UV (200-300 nm). One of the dramatic results with the Hubble Space Telescope (HST) is that these distant objects resemble nearby late-type galaxies, but are they really similar classes of objects? This is a critical issue for understanding the process of galaxy formation. We therefore present a systematic imaging survey with the Hubble Space Telescope/Wide Field Planetary Camera-2 of nearby galaxies in the rest-frame mid-UV and in the red (800 nm). The sample covers a wide range of galaxy types and inclinations. Most objects have ground-based optical images (360-700 nm), and some have near-IR images (1.25-2.2 micron), or far-UV images (150 nm; from ASTRO/UIT).

I will discuss the panchromatic properties of these galaxies from this ongoing HST project. Results will be shown separately for early-type galaxies, mid-type spirals, and for late-type, irregular, and peculiar/merging galaxies. In conclusion, when observed in the rest-frame mid-UV, early- to mid-type galaxies are more likely to be misclassified as later-types than late-type galaxies are misclassified as earlier-types. The apparent change of galaxy morphology with rest-frame wavelength can explain part, but not all of the excess faint blue late-type galaxies seen in the deepest HST fields.

Finally, I will show what galaxies like these would look like to the Next Generation Space Telescope (NGST), if they were observed in their restframe UV, and if they existed as observed nearby but at redshifts z=1 to 15.

Jul. 18 @ 16:00
Rodrigo Ibata (Strasbourg)
Title: Streams, Clumps and Dark Bumps ... in galaxy halos
Galaxy formation models, particularly the popular models based on Cold Dark Matter (CDM), have focussed their attention on galaxy halos, since these are overwhelmingly the most important components of galaxies in terms of their mass. Observationally, however, very little is known about these dark regions of galaxies, and even less is known About the ``outer halo'' regions, where structures can survive the disruptive Galactic tidal forces for more than a Hubble time. The advent of powerful wide-field cameras and wide-field multi-object spectrographs, now brings the study of these low-density outer regions of galaxy halos within reach. If CDM theory is correct, there should be about a hundred halo substructures in this volume. I will review our several searches for substructures in the halos of the Milky Way and Andromeda galaxies, the two best targets for this study, and discuss how the detected structures can be used to illuminate the dark and immensely massive region they inhabit.
Jul. 15 @ 16:00
Lisa Germany (ESO)
Title: Type Ia Supernovae in the Infrared
By now just about everyone in the astronomical world must realise the usefulness of Type Ia Supernovae (SNIa) for measuring distances - the high-redshift SN teams certainly made sure of that! However, most of this current work has been done in the optical, where extinction is a problem and has been used by some to question the accelerating universe result. Extinction is less of a problem in the IR, so what research has gone into investigating SNIa at these wavelengths? In addition, we have discovered many "unusual" SNIa in the optical which do not neatly fit into one of the established classifications. Are they "unusual" in the IR as well? In this talk I will present a short review on the current status of SNIa research in the IR.
Jun. 21 @ 11:30
Martin Ward (Leicester)
Title: The Decadal Plan for ESA's Science Programme
The European Space Agency spends close to 1M euros per day, on its Space Science programme (excluding the Space Station, Earth observation amd telecommunications activities). This is a small fraction of the NASA spend. Nevertheless ESA competes, and indeed leads, in many areas of Space Science. I will present an overview of ESA's future plans for the next decade and beyond. This will be a programmatic review, but I will refer to the main science drivers for the missions.
Jun. 13 @ 16:00
Michael Burton (UNSW)
Title: Hot Molecular Cores and the Earliest Stages of Massive Star Formation
Jun. 5 @ 16:00
Matthew Colless (ANU)
Title: The 2dF and 6dF Galaxy Surveys
Observations for the 2dF Galaxy Redshift Survey are now complete. The 2dFGRS has measured redshifts for 221,283 galaxies out to z=0.3 over 5% of the sky. I will summarize the results so far from the survey on the determination of cosmological parameters and the characterization of the properties of the large-scale galaxy distribution. I will also review the current status and future plans of the 6dF Galaxy Survey.
Jun. 3 @ 11:00
Peter Cottrell (Centerbury)
Title: The Southern African Large Telescope (SALT) Project: A Condiment for the 21st Century!
May. 31 @ 11:00
Erwin de Blok (ATNF)
Title: The Dark Matter Density Profiles of Low Surface Brightness Galaxies
High-resolution rotation curves of a sample of over 50 dark matter dominated galaxies show that the inner mass density profiles are dominated by central constant density cores, inconsistent with the steeply rising Cold Dark Matter profiles derived from N-body simulations. We show that systematic or observational effects cannot explain the data, leading to the inevitable conclusion that the predictions of CDM at small scales are incorrect.
May. 30 @ 16:00
Thijs van der Hulst (Groningen)
Title: HI in Elliptical Galaxies
VLA imaging of some 20 elliptical galaxies in the HI 21-cm line provide an overview of the variety of morphologies that exist. Half of the sample consists of elliptical galaxies with optical fine structure such as shells and central dust structures. The other half are optically undisturbed. The HI is often rotating regularly and suggests disk like structures. The data will be discussed within the framework of the idea that the HI in gas-rich elliptical galaxies is captured from satellite objects.
May. 2 @ 16:00
Naomi McLure-Griffiths (ATNF)
Title: The HI Southern Galactic Plane Survey
The HI Southern Galactic Plane Survey (SGPS) is a survey of the neutral hydrogen (HI) spectral line and 21 cm continuum emission in the fourth quadrant of the plane of the Milky Way. The survey is part of a large international effort to understand the structure, dynamics and thermal phases of the interstellar medium by studying the HI throughout the disk of the Galaxy. The SGPS combines data from the Australia Telescope Compact Array (ATCA) and the Parkes Radio Telescope for complete coverage of structures ranging in angular size from 2 arcminutes to 2 degrees. We are using the SGPS dataset to study the properties of large scale emission structures in the ISM, specifically HI shells, supershells, and chimneys. HI shells are among the largest objects in the ISM with radii between tens of parsecs and kiloparsecs. As such, they are a major constituent in the Galactic energy budget and drive much of the dynamics of the ISM. HI shells, which are formed through the combined effects of stellar winds and supernovae, outlast the radiative lifetimes of their parent HII regions and supernova remnants and thereby provide lasting fossils of the effects of massive stars on the ISM. In this talk I will describe the SGPS survey goals and data products. I will present a new catalog of large HI shells in the Southern Milky Way, focusing on several interesting examples of shells, including two chimneys. I will also discuss the Galactic distribution of shells and how they can be used to trace the history of star formation in the Galaxy.
Apr. 22 @ 16:00
Mike Dopita (ANU)
Title: The Dynamical Interaction of AGN with their Galaxian Environments
It is now clear that jet-driven shocks in a variety of classes of active galaxies are responsible for an important fraction of the emission of the extended narrow-line regions (ENLR). Nontheless, this cannot explain all the observations, and it is clear that the remainder arises from photoionization by UV photons originating at the active nucleus itself.

I will present two-dimensional hydrodynamic models from the RSAA group which including cooling to support a model whereby the shock-excited NLR are in a jet-driven early phase of their evolution. When the jet breaks out into the low-density surrounding regions, the pressure driving these shocks drains away and they go into a momentum-conserving phase of evolution, during which the ionizing photons from the central engine replace shocks as the exciting mechanism. During this phase, shock induced star formation may be important.

In their photoionized phase, the similarity between the emission spectra of narrow line regions has long been a mystery. The implication of the emission line diagnostics is that the ionization parameter is nearly always the same. I will present dusty radiation-pressure dominated photoionization models that can solve this problem, and also explain the fast (3000 km/s) outflows seen in some Seyferts.

Mar. 27 @ 16:00
Steven Tingay (ATNF)
Title: The Sub-Parsec-Scale Structure and Evolution of Centaurus A
Mar. 21 @ 16:00
James Murray (Leicester)
Title: Supercomputing Simulations of Astrophysical Discs
Wherever there is rotation and gravity, a disc can be found. Computational tools originally constructed to study cataclysmic variables (close binaries consisting of a white dwarf accreting froma low mass companion) are now being applied to discs in other contexts. I will discuss calculations of discs in X-ray transients and around young stellar objects. Supercomputers have played a key role in our eforts to understand the inner workings of accretion discs. Where once we constructed one and two dimensional models, we are now able to resolve all three dimensions and are seeing significant differences in results.
Mar. 14 @ 16:00
Chris Flynn (Tuorla/Swinburne)
Title: White Dwarfs and Galactic Dark Matter
Part of the dark matter in the Milky Way might be in the form of old, dim white dwarfs. Quite a number of searches are currently going on to find such white dwarfs directly --- and cool, dim, fast moving white dwarfs are turning up. Although the jury is not yet in on whether the dark matter has finally been detected directly, there are some very interesting results. I'll argue here though that most if not all of what has been found so far can be understood without invoking a new population of "dark halo white dwarfs".
Feb. 21 @ 16:00
Mike Disney (Cardiff)
Title: The Discovery Potential of any Astronomical Instrument (or ... how to make discoveries!)
Jan. 18 @ 11:00
Bill Harris (McMaster)
Title: Stalking the Fundamental Plane: Are Globular Clusters Universal?
At least in the Milky Way, globular clusters are amazingly simple dynamical structures that fall into a 1.5-dimensional family. Is the same true in very different types of galaxies? I will discuss new HST-based imaging data for globular clusters in NGC 5128 which show where they lie on the "fundamental plane" of structural parameters relative to the Milky Way.