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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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2004 Colloquia

Dec. 10 @ 16:00
Erwin de Blok (ANU)
Title: The Cores of Dark Matter Halos - A Problem for CDM?
Low Surface Brightness galaxies are dominated by dark matter. recent high-resolution rotation curves suggest that their total mass-density distributions are dominated by constant density cores, rather than the steep and cuspy distributions found in Cold Dark Matter simulations. We have modelled the impact of many systematic observational effects, and find that no single effect can reconcile the data with cuspy CDM halos. The data are best described by a model with a soft core with an inner power-law mass-density slope alpha= -0.2 +/- 0.2. No single universal halo profile provides an adequate description of the data and the observed mass profiles appear to be inconsistent with LambdaCDM simulations. I will discuss some new observations that may contribute to a solution for this longstanding problem.
Dec. 9 @ 16:00
Eric Wilcots (Wisconsin)
Title: Diffuse Hot Gas in Spiral Galaxies
The Sun resides within a several hundred parsec bubble devoid of neutral gas, but filled with a diffuse X-ray emitting plasma. X-ray observations over the past two decades show us that there are a number of similar bubbles throughout the Milky Way, but the true filling factor of hot gas in our Galaxy remains unknown. This is largely because of the difficulty of observing X-ray emission from our location within the Galactic disk. The high resolution and good sensitivity of the Chandra X-ray Observatory, however, makes it possible to accurately map the distribution of diffuse hot gas in other spiral galaxies. In this talk I will review a number of recent efforts to understand the physical properties of the diffuse hot interstellar medium and address the question of the filling factor of hot gas in spiral galaxies.
Dec. 8 @ 16:00
Chris Power (Swinburne)
Title: Mass Profiles of Cold Dark Matter Halos
As controversies in cosmology go, the "small scale crisis" that (either) faces (or has faced) CDM (depending on your persuasion) is perhaps the most intriguing. A theoretical framework that has proven to be so robust over the last two decades (save for the addition of a dark energy component) robustly predicts a cuspy structure -- i.e. divergent central densities -- for dark matter halos that appears to be sorely at odds with mass models derived from observations... but could the devil lurk in the details?

Significant intellectual effort has been expended since the seminal Flores & Primack (1993) and Moore (1994) papers, which first highlighted the discord between theory and observation, to quantify the discrepancy and to understand its origin. Observers can now draw upon high resolution datasets, free from any potentially insidious systematics, when constructing their mass models. Similarly, numerical cosmologists now routinely perform simulations of individual dark matter halos containing several million particles within their "virial" radii, and can confidently determine the extent to which numerical artifacts (driven by the approximations inherent in N-body algorithms) impact upon their structure.

In this talk, I will discuss results from recent studies that have investigated CDM halo structure and how these compare with observationally derived mass profiles. I will explain why we feel confident that cuspy halos are "physical" rather than driven by numerics and a robust prediction of the CDM model, and how numerical studies appear to have converged on the value of the inner slope of the mass profile. Finally I will briefly discuss other tests of halo structure that may be sensitive to the nature of the dark matter and could thus offer an alternative method with which it could be probed.

Dec. 1 @ 16:00
Chris Sneden (Texas)
Title: Neutron-Capture Nucleosynthesis in the Early Galaxy
We review recent observational progress on the origin and buildup of neutron-capture (n-capture: Z>30) elements in the Galaxy. We proceed from the particular to the general, starting with a discussion of a detailed abundance distribution of a few very metal-poor stars that possess enormous relative overabundances of rapid n-capture synthesis products. The pivotal role played by atomic physicists in this work is highlighted. Then the overall trend in rapid-to-slow n-capture abundances is discussed. Finally, the possible use of thorium and uranium in Galactic age is examined using new data for thorium in a large sample of metal-poor stars.
Nov. 25 @ 16:00
Jeremy Bailin (Swinburne)
Title: Alignment of Galactic Components in Models of Galaxy Formation
With high resolution cosmological N-body simulations, the internal alignment of the shapes and angular momenta of a large number of dark matter halos can be studied in unprecedented detail, as can alignment of the shapes and angular momenta of these halos with respect to the large scale structure. I will discuss some results of one such simulation, including the orientation of the halos, rotation of the halo shape, and some implications that misalignment between various galactic components have on warped galactic disks.
Nov. 18 @ 16:00
Patricia Sanchez-Blazquez (Swinburne)
Title: Unraveling the Star Formation History of Elliptical Galaxies
Early-type galaxies are excellent laboratories for the understanding of the processes involved in the formation and evolution of galaxies with look-back time, and for addressing cosmological issues, such as the epoch of galaxy formation or the nature of the objects observed at high redshift. In this talk I will present the first results of our investigation into the star-formation history of early-type galaxies in the Local Universe through the analysis of their stellar populations. Our sample includes early-type galaxies with a fair range of luminosities located in environments of different density. Through the analysis of ages, metallicities and "qualitative" chemical abundances ratios we have obtained results that are in accordance with the view that galaxies in low density environments have experienced a more extended history of star formation than their counterparts in dense clusters.

On the other hand, whilst the new generation of large telescopes is already generating high quality spectra for low and high redshift galaxies, the stellar populations models suffer from a lack of extensive empirical stellar libraries to successfully interpret the observational data. I will present a new stellar library which overcomes some of the principal shortcomings of the previous ones. The library span an unpredecent coverage of atmospheric parameters and will consitute a powerful tool to synthetise the spectral distribution of galaxies as well as to recalibrate new, more age and metallicity sensitives line-strength indices.

Nov. 11 @ 16:00
Sarah Brough (Swinburne)
Title: Brightest Cluster Galaxies and their Environment
The central brightest galaxies in clusters have been used as cosmological probes since the work of Sandage and his collaborators in the 1960s. However, it became apparent that brightest cluster galaxies (BCGs) were unsuitable as distance indicators owing to signs that they have evolved over the timescales examined. Their position at the centres of clusters and groups of galaxies uniquely links their formation and evolution with their environment, yet the mechanisms of this process are still unclear. As the most massive galaxies at all epochs they enable a unique test of structure formation models as hierarchical models suggest that they must have assembled their stellar mass most recently. We are investigating the mass evolution of BCGs and how that depends on their environment, using a large sample of BCGs in X-ray selected clusters with redshifts 0.02 < z < 0.8. We observe that the BCGs in the most X-ray luminous clusters show no evidence of mass growth since z ~ 1, in contrast to those in the least X-ray luminous clusters which show a wide range of mass growth in the same time interval.
Nov. 4 @ 16:00
Michael Balogh (Waterloo)
Title: How to Kill a Galaxy: Stripping, Harassment, Strangulation and More
The evolution of galaxies is governed both by local processes, and by interactions with the surrounding environment. In this talk I review (primarily) observational progress in our understanding of how hostile environments terminate star formation in galaxies. Specifically, the SDSS and 2dFGRS surveys allow a detailed analysis of the correlations between galaxy properties and their environment at the present day. We can use these surveys as a baseline to trace evolution in both rich clusters and, more recently, galaxy groups. These new results show that group environments are likely responsible for rapid transformations between gas-rich, star forming galaxies and the elliptical, passively-evolving population that dominates today's clusters.
Oct. 21 @ 16:00
Lisa Kewley (Hawaii)
Title: Cosmic Star Formation and the Metallicity History of Galaxies
Observing the star formation rate since the earliest times in the universe is crucial to understanding galaxy formation and evolution. Metallicity is intricately related to star formation because metals are injected into the interstellar medium by stellar mass-loss processes. Theory suggests that metallicity changes less rapidly than star formation rate as a function of redshift, but until now, there has been no solid observational foundation for the cosmic metallicity history of star-forming galaxies. I will present the first results of our new investigation into the star formation and metallicity history of galaxies between redshifts 0 and 3. Our local comparison samples include the Nearby Field Galaxy Survey (NFGS) and an objectively selected sample of galaxy pairs. We find that the galaxy pairs contain a broader range of star formation and metallicity properties than observed in the NFGS, providing an important local benchmark for comparisons with high-z samples. I compare the star formation and metallicity properties of our local samples with a large sample of galaxies from the Hubble Deep Field North and the Gemini Deep Deep Survey. This analysis provides insight into the simultaneous evolution of star formation and metallicity for star-forming galaxies spanning the redshift range 0 to 3.
Sep. 24 @ 11:00
Tim Cornwell (NRAO)
Title: The Square Kilometer Array: The Computing Challenges
New developments in all fields of astronomy have brought the current generation of astronomers to the brink of probing the origin and evolution of the Universe as a whole. To attack these questions directly, a new generation of astronomical facilities is needed with a revolutionary new instrument at radio wavelengths playing a critical role. The Square Kilometre Array, a radio telescope with an effective collecting area more than 30 times greater than the largest telescope ever built, will reveal the dawn of galaxy formation, as well as many other new discoveries in all fields of astronomy. The technical challenges to be overcome in the construction are manifest, the chief being that of constructing large collecting areas at low costs. Perhaps second to that is the challenge of processing the data collected by the SKA. The data analysis problem is large in size and difficult in technique. The cost of the data processing hardware could reach hundreds of millions of dollars, even a decade from now. The software development costs are likely to be also high. The imaging performance needed to achieve some of the scientific goals is considerably beyond the current state of the art. I discuss these various challenges and the prospects (good) for meeting them.
Sep. 16 @ 16:00
Rachel Deacon (Sydney)
Title: Water and OH masers in Post-AGB Stars
Radio maser lines from several molecules including OH, water and SiO are good tracers of the shapes and kinematics of circumstellar shells around evolved stars. In particular post-asymptotic giant branch stars, which are the (largely non-visible) precursors to planetary nebulae, reveal much of their nature through observations at these wavelengths.
I will be presenting results from maser observations of 87 post-AGB stars, in particular the results of 22 GHz water maser observations recently completed at Tidbinbilla. Three stars show evidence of high-velocity (50 km/s+) outflows which could be the mechanism via which these stars change from their spherical AGB morphologies to the asymmetric morphologies most common in planetary nebulae.
I will also cover selection of the sample, and the main findings from the OH observations (Deacon, Chapman and Green, submitted to ApJ).
Sep.10 @ 11:00
Chris Tinney (AAO)
Title: The Future of the Anglo-Australian Observatory
The "AAO of the Future" strategic plan is now almost 5 years old, and many of the changes to the AAO's make-up and operations it envisaged have come to pass, or will soon be reality. The AAO is now providing Australia with a major player in the world instrumentation market, the UK is modifying its role within the AAO, and plans are now being made for the AAT's operational mode over the coming years .... I'll update you all on these and other facets of the AAO.
Sep. 9 @ 16:00
Chris Tinney (AAO)
Title: From Brown Dwarfs to Extrasolar Planets, and Beyond ...
The study of the smallest and coolest objects (brown dwarfs and planets) is a field driven by new observations and new results - theory has proved to have little predictive power in understanding either the properties of brown dwarfs and planets, OR their frequency. Fortunately, for observers this makes for an exciting time. Almost every observing run offers the prospect of new results and new understanding. I'll report on some recent parallax and methane imaging results for brown dwarfs, the progress of the long-running Anglo-Australian Planet Search, and the avenues opening up ahead of us in the future, especially in searches for 'free-floating planets' and expanded radial velocity searches.
Jun. 17 @ 16:00
Ralpha Sutherland (ANU)
Title: Radio-Jets, Starbursts, and Galaxy Halo Interactions
Galaxies form out of small fluctuations in a smoothly expanding Universe. However, the initial gravitational collapse phase is accompanied by the formation of supermassive black holes and clusters of massive stars. Evolution beyond this point, however, is anything but simple. Black holes and star clusters generate powerful outflows in the form of jets and superwinds that interact with still infalling gas, possibly regulating the galaxy formation process, initiating new sites of star formation, and carrying chemically enriched gas to the intergalactic medium. Unfortunately, beyond this qualitative description our detailed theoretical understanding is poor.

I will present new results from 3D simulations of a GPS/CSS galaxy, with gravitational potentials included, which shed some new light on the jet driven outflow process in particular.

Jun. 10 @ 16:00
Michael Ashley (UNSW)
Title: Life, The Universe, and Everything
The high plateau that covers half of the continent of Antarctica contains the best observing sites on Earth. The infrared sky background is low, the precipitable water vapour is low, the sub-millimetre sky opacity is low, the winds are low, the atmosphere is exceedingly clear and stable, it never rains, there is no dust, and it is geological stable. The one parameter that had not been quantified was the astronomical seeing during wintertime.

Over the last three months, our group at UNSW has succeeded in measuring the seeing at Dome C, a remote location at a latitude of 75S. The measurements were made using a robotic observatory containing a small telescope and a Multi-Aperture Scintillation Sensor. The results are spectacularly good.

The talk will describe the various techniques for measuring seeing, how we did it remotely at Dome C with no humans present, and the implications of the results for the next generation of Extremely Large Telescopes.

May. 28 @ 16:00
Alexander Knebe (Swinburne)
Title: Life, The Universe, and Everything
Apr. 22 @ 16:00
Giuseppina Battaglia (Groningen)
Title: Kinematics of Milky Way Halo Tracers
Thus far, the dynamical modelling of the Milky Way has been mostly restricted to the inner Galaxy. The outer Galaxy provides a unique environment to constrain the dark halo properties and to test the fundamental prediction of the hierarchical paradigm, namely that its density should follow a NFW profile.

Halo stars offer the opportunity to trace the Milky Way potential out to very large distances (beyond 100 kpc) from the Galactic centre. For a sample of giants stars, globular clusters, FHB stars and satellite galaxies, we determine how the radial velocity dispersion varies as a function of the radius, out to distances of 120 kpc. We compare these observations to different models of the Galactic potential and determine the size and velocity anisotropy that best fit our data.

Apr. 16 @ 16:00
Heath Jones (ANU)
Title: Galaxy Surveys Near and Far
I will summarise current progress on two very different galaxy surveys: The 6dF Galaxy Survey of the local universe, and a survey for Lyman-alpha emission-line galaxies at redshift 5.7.

The 6dF Galaxy Survey aims to measure the redshifts of around 150,000 galaxies, and the peculiar velocities of a 15,000-member sub-sample, over almost the entire southern sky. When complete, it will be the largest redshift survey of the nearby universe, reaching out to about z=0.15, and more than an order of magnitude larger than any peculiar velocity survey to date. An online database is available, with the first of three public data releases having taken place in March 2004.

I will also speak about an unrelated survey for high-redshift emission line galaxies. We have recently completed deep multi-band observations with the ESO Wide-Field Imager for Lyman-alpha-emitting galaxies at z=5.7. This survey covers 3 to 7x the volume of earlier work, allowing an unprecedented determination of the emission-line luminosity function at this redshift. Spectroscopic confirmation of our first candidate will be presented.

Mar. 10 @ 16:00
George Hobbs (ATNF)
Title: Long-term Timing of Pulsars
I present results from analysing the timing residuals of 374 pulsars with data spanning up to 34 years. First, I'll discuss measurements of linear dispersion measure gradients that are well modelled using a thin scattering screen. Second, the meaning of frequency second derivative values and their relationship to pulsar braking indices and timing noise and thirdly, the astrophysics obtainable from 236 proper motion measurements. I'll conclude by mentioning current work to update the most commonly used pulsar timing package TEMPO.
Feb. 5 @ 16:00
Alan McConnachie (Cambridge)
Title: Galaxies in the Local Group
he Local Group provides a unique opportunity to study in detail the structure and evolution of a variety of galaxies, gaining insight into the processes that lead to their formation and subsequent evolution. In recent years, new technologies have enabled us to gain an unprecedented view of these objects, both photometrically and kinematically. Over the last three years we have been using the Wide Field Camera on the Isaac Newton Telescope to conduct a large photometric survey of the halo of the Milky Way's sister galaxy, M31, which now extends to a projected distance of over 60kpc from the centre of this galaxy. We have since extended the scope of this study to include a survey of M33 and to include photometry of all of M31's satellites, in addition to an ambitious kinematic survey of RGB stars in M31. Such a large database allows for a wealth of scientific studies and I will present new results on the prevalence and nature of substructure and tidal streams within the halo of M31. Additionally, I describe a new technique for accurate distance determination using the Tip of the Red Giant Branch in old stellar populations - a technique that we have successfully applied to the satellites of M31 to probe their spatial distribution, and which has yielded tantalising evidence concerning he origin of these objects.
Feb. 4 @ 16:00
Daniel Price (Cambridge)
Title: A Comparison of the Jet Acceleration Mechanisms in Young Stellar Objects and Active Galactic Nuclei
We examine the hypothesis that there exists a simple scaling between the observed velocities of jets found in Young Stellar Objects (YSOs) and jets found in Active Galactic Nuclei (AGN). Employing simplified physical models of the jet acceleration process, we use time-dependent, spherically symmetric wind models in Newtonian and General Relativistic gravitational fields to ask whether the energy input rates required to produce the jet velocities observed in YSOs (of about 2 times the escape velocity from the central object) can also produce AGN jet velocities (Lorentz factors of about 10). Such a scaling would be expected if there is a common production mechanism for such jets. It can be demonstrated that such a scaling exists, provided that the energy input process takes place sufficiently deep in the gravitational potential well, enabling physical use to be made of the speed of light as a limiting velocity, and provided that the energy released in the accretion process is imparted to a small fraction of the available accreting material.
Jan. 8 @ 16:00
Christof Keller (Heidelberg)
Title: Transport of Matter in Protoplanetary Accretion Discs
Crystalline dust observed in the outer, cold regions of protoplanetary discs requires conditions for its formation, which are typical for the warm, inner regions of the disc. Also calcium aluminium rich inclusions, found in meteoritic material, coming from the asteroidal zone of our own solar system require hot temperatures for their formation. These findings suggest the existence of a mechanism, which allows an efficient, outward-directed radial transport of material in accretion discs. I will present numerical and semi-analytical results on flow structures of gas and dust particles in accretion discs and discuss the impact of advective and diffusive transport on the radial mixing of material within protoplanetary discs.