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Previous Seminars
Listed here, in reverse chronological order, are presentations that have been
given recently at the
2008
- New
results on an old problem: Deep Mixing in Giant Stars
Who: Professor John
Lattanzio (Centre for Stellar and Planetary Astrophysics,
Where: Geoff Opat Seminar Room 360, School of Physics
When: 13 Aug 08 at 3:15pm – postponed. TBA.
Abstract: Low mass stars are nett producers of 3He. They produce enough to explain all the 3He seen in the Universe. This is inconsistent with the results of Big Bang Nucleosynthesis which also produces enough 3He to explain the observations. Similarly, for over 30 years we have known that there is some form of mixing in radiative zones in stars. We see abundances changing in stars and know the mixing is there. I will show a new mechanism we discovered during calculation of stellar structure in 3D which solves both problems.
- What
is the Lindau-Nobel Laureates meeting?
Life after a
physics Ph.D. - Direct Exchange Geothermal Heat Pumps
Who: Donald
Payne
Where: Geoff Opat Seminar Room 360, School of Physics
When: 6 Aug 08 at 3:15pm
Abstract:
What is the Lindau-Nobel Laureates meeting?
I'll share some reflections on the 58th Meeting of the
Nobel Laureates in
Life after a physics Ph.D. - Direct Exchange Geothermal
Heat Pumps
I'll share some of my activities after completing a Ph.D with a brief overview
of what Direct Exchange Geothermal Heat Pumps are and how they may play their
part in addressing Australia's 2020 Mandatory Renewable Energy Target.
- The
chemistry and dynamics of star formation in the G333 molecular cloud
complex
Who: Maria
Cunningham,
Where: Geoff Opat Seminar Room 360, School of Physics
When: 16 July 08 at 3:15pm
Abstract: G333 Survey is a multi-wavelength survey of the G333 / RCW 106 region, aiming to put together a comprehensive picture of massive star formation throughout an entire giant molecular cloud complex. The aim of the project is to to answer observationally some of the key questions about the dynamical processes surrounding massive star formation (e.g. massive stellar winds and large-scale galactic flows) and their relative importance in regulating the star formation process. These dynamical processes drive the turbulent motions which are ubiquitous in giant molecular clouds (GMCs).
We have used the new broadband capabilities of the Mopra telescope to map the distribution of around 20 different molecules in an approximately 1 degree square region of the southern Galactic plane (the G333.6-0.2 giant molecular cloud complex). The multi-molecular line nature of this survey is what distinguishes it from similar surveys, and is crucial for gaining a clear picture of the energetics and dynamics of the gas. Different molecular transitions trace different regions of gas in terms of density and excitation, and so can be used to follow energy transfer through the molecular cloud complex. Our initial investigations of the spatial power spectrum of molecules which trace different critical densities show a picture where turbulence is injected at large scales (hundreds of parsecs), and passes through to smaller parsec scales without significant dissipation.
This scenario is supported by other analyses which suggest that the initial wave of star formation in the complex may have been triggered by a merger between two large scale Galactic flows, but that the majority of current star formation has clearly been triggered by relatively nearby dynamic events associated with massive star formation, such as expanding shells.
- Seminar:
ATLAS: Probing Galaxy and AGN evolution over cosmic time:
Who: Prof Ray Norris (ATNF)
Where: Level 7 Conference Room 760,
When: 26 June 08 at 3:15pm
Abstract: ATLAS is the largest deep radio survey so far attempted, which is distinguished even more by its comprehensive multi-wavelength approach.
We are gradually amassing an enormous dataset of radio-selected galaxies to tackle questions such as:
* What is the evolutionary relationship between starbursts and AGN?
* Does the radio-FIR correlation change with redshift or with galaxy properties?
* Are there rare objects that are only found in a wide/deep survey like this?
* What is the origin of the cosmic magnetic field?
Although the project is far from complete, we are already
starting to answer some of these questions, and have stumbled across some surprises
along the way, such as radio-loud galactic nuclei embedded within spiral
galaxies, objects which are bright at radio wavelengths but unexpectedly faint
in the infrared, and their opposite numbers which are bright in the infrared
but anomalously weak at radio wavelengths.
- Seminar:
Cosmic Ray Ion and Electron Acceleration in
Relativistic Extragalactic Jets
Who: Matthew
Baring,
Where: Geoff Opat Seminar Room 360, School of Physics
When: 18 June 08 at 3:15pm
Abstract: Diffusive shock acceleration
(DSA) at relativistic shocks is expected to be an important acceleration
mechanism in a variety of astrophysical objects including extragalactic jets in
active galactic nuclei and gamma ray bursts. In this talk, key predictions of
DSA at relativistic are outlined, to guide the interpretation of astronomical
data. We present results from a
- Seminar:
Searching for the Electromagnetic Counterparts of
Supermassive Black Hole Mergers
Who: Bence
Kocsis,
Where: Geoff Opat Seminar Room 360, School of Physics
When: 11 June 08 at 3:15pm
Abstract: The anticipated detection of the gravitational waves (GWs) by the future Laser Interferometric Space Antenna (LISA) will constitute a milestone for fundamental physics and astrophysics. In this talk, I will discuss LISA's capability of localizing supermassive black hole (SMBH) mergers by measuring the GW signal emitted during the last year of inspiral preceding the coalescence. While the GW signatures themselves will provide a treasure trove of information, if the source can be securely identified in electromagnetic (EM) bands, this would open up entirely new scientific opportunities, to probe fundamental physics, astrophysics, and cosmology.
I will describe several mechanisms that might produce EM variability during a SMBH merger. The binary may produce a roughly periodic variable electromagnetic flux due to the orbital motion prior to coalescence, a transient signal caused by shocks in the circumbinary disk when the SMBH binary recoils and "shakes" the disk, or a prompt EM flare caused by the viscous dissipation of GWs in the ambient gas. Future wide-field EM surveys will be able to search for these time--variable signatures in the 3 dimensional error volume provided by LISA weeks before the merger.
- Seminar:
First science from the WiggleZ Dark Energy Survey
Who: Scott Croom,
Where: Geoff Opat Seminar Room 360, School of Physics
When: 29 May 08 at 3:15pm
Abstract: Dark Energy is one of the biggest current questions in cosmology, and one of the best ways to measure it is using baryonic acoustic oscillations (BAO). These weak signals in the large scale structure of the galaxy distribution give us a standard ruler with which to measure the expansion history of the Universe. The WiggleZ survey on the Anglo-Australian Telescope is the only current BAO survey. I'll describe the survey and discuss some of the first science results.
- Seminar:
Unveiling the nature of Seyfert nuclei with 1 -
100 micron spectral energy distributions
Who: Catherine Buchanan,
Where: Level 7 Conference Room 760,
When: 21 May 08 at 3:30pm
Abstract: The infrared is a key wavelength regime for probing the dusty, obscured nuclear regions of active galaxies. We present results from an infrared study of 87 nearby Seyfert galaxies using the Spitzer Space Telescope and ground-based telescopes. Combining detailed modelling of the 3 - 100 micron spectral energy distributions with mid-IR spectral diagnostics and near-infrared observations, we find broad support for the unified model of AGNs. The IR emission of Seyfert 1s and 2s is consistent with their having the same type of central engine viewed at a different orientation. The nature of the putative torus is becoming clearer; in particular we present evidence that it is likely a clumpy medium. Mid-infrared correlations between tracers of star formation and AGN ionizing luminosity reveal the starburst-AGN connection implied by the black hole/bulge mass relation, however it is not yet clear if this is due to feedback.
- Seminar:
Magnetic activity in protostellar disks
Who: Raquel Salmeron,
Where: Geoff Opat Seminar Room 360, School of Physics
When: 15 May 08 at 3:15pm
Abstract: Star formation is induced by the gravitational collapse of molecular clouds cores. During this phase, angular momentum conservation results in the progressive increase of the centrifugal force, which eventually halts the infalling matter and leads to the development of a central mass ('protostar') surrounded by a disk of material. In the presence of an angular momentum transport mechanism, mass accretion onto the protostar proceeds through this disk, and it is believed that this is how stars typically gain most of their mass. The mechanisms responsible for this transport of angular momentum are not well understood. The most promising are turbulence viscosity induced by the magnetorotational instability and the centrifugal acceleration of outflows. Both processes are powered by the action of magnetic fields and are, in turn, likely to play key roles in the structure, dynamics and evolution of these systems. The weak ionization of protostellar disks, however, may prevent the magnetic field to effectively couple to the gas and drive these processes. In order to study the magnetic activity of these disks under realistic conditions, we have developed a quantitative scheme that incorporates their detailed ionization structure and all relevant field-matter diffusion mechanisms. In my talk I examine the viability and properties of magnetically driven processes in protostellar disks, present our solutions and explore the implications of the resulting disk structure to planet formation and migration.
- Seminar:
HI in Galaxies at Moderate Redshifts: Current and Future Observations
using Optical Redshifts for HI Coadding
Who: Philip Lah,
Where: Level 7 Conference Room,
When: 30 Apr 08 at 1pm
Abstract: It is known that the rate at which stars are produced in galaxies has dropped by a factor of ten in the last 9 billion years (from z ~ 1.0). However, the gas content of galaxies - the fuel supply for star-formation - is only poorly constrained by observations during this period of time.
Quantifying the atomic neutral hydrogen gas (HI) content of galaxies using 21 cm emission from distant galaxies (z > 0.1) is difficult with current radio telescopes due to the low flux of the line. However, the average HI content of galaxies at moderate redshifts can be measured by coadding the HI signal from multiple galaxies with known optical positions and redshifts. Our group has been pioneering this technique using the Giant Metrewave Radio Telescope (GMRT) and the Anglo-Australian Telescope (AAT).
I will present our current results for the average neutral hydrogen gas content in 121 star forming galaxies at a redshift 0.24 (look-back time of
2.8 Gyr) and the gas content of
324 galaxies surrounding the galaxy cluster Abell 370 at a redshift of 0.37
(look-back time of 4.0 Gyr). I will
also discuss the use of the HI coadding technique with the SKA pathfinders and
show that they can be used to quantify the average HI content of galaxies out
to redshifts of 1.0.
- Seminar
Who:
Where: Geoff Opat Seminar Room 360, School of Physics
When: 8 May 08 at 3:15pm
Abstract: TBA
- Seminar:
Looking for the most distant quasars and the coldest stars with UKIDSS
Who: Daniel
Mortlock,
Where: Geoff Opat Seminar Room 360, School of Physics
When: 17 Apr 08 at 11am
Abstract: The UKIRT Deep Infrared Sky Survey (UKIDSS) is the largest near-infrared survey ever undertaken, going ~3 mag deeper than the 2 Micron All-Sky Survey (2MASS) over an area matched to the Sloan Digital Sky Survey (SDSS).
One of its primary scientific
goals is extending the work of 2MASS and SDSS in finding the most distant
quasars and the coolest sub-stellar objects. After a general introduction to infrared
astronomy and UKIDSS I will describe both the difficulties and successes of
these ambitious endeavours.
- \Colloquium:
Varying fundamental constants? Observational status and future prospects
Who: Dr Michael
T. Murphy, QEII Research Fellow, Centre for Astrophysics & Supercomputing,
Where: Hercus Theatre
When: 15 Apr 08 at 12-1pm
Abstract: Variations in the fundamental constants would directly violate the Standard Model of particle physics and Einstein's equivalence principle. Many modern unified theories actually predict variations in the (low-energy) values of the constants, linking them to changes in the typical sizes of extra, compactified dimensions of space. Many dedicated laboratory and satellite experiments currently test for variations over several-year timescales but it is essential to probe a much larger range of times and distances. Remarkably, absorption systems along the sight-lines to distant quasars offer our most precise extragalactic probe of variations in the fine-structure constant and the proton-to-electron mass ratio. I will discuss the current evidence for and against variations in both these fundamental parameters. I will also describe the potential of newly proposed spectrographs on current and future telescopes for constraining fundamental physics at high redshifts at a precision competitive with advances in laboratory experiments. Calibrating these spectrographs poses a particular challenge and I will outline our proposal for doing so with new laser frequency comb technology.
- Seminar: Dark
Energy and the Hubble Constant
Who: Dr Jim
Condon, NRAO,
Where: Geoff Opat Seminar Room (360), School of Physics
When: 28 Feb 08 at 3:15 – 4:15pm
Abstract: Dark
energy (DE) dominates the energy density and future expansion of the universe,
and its nature is a major unsolved problem for theoretical physics. The equation-of-state
and energy density of DE can be constrained observationally by comparing an
accurate (< 3% rms) value of the Hubble constant with the known distance to
the last-scattering surface of the cosmic microwave background. The Megamaser
Cosmology Project (MCP) is now measuring geometric distances to water masers in
the nuclei of distant Seyfert galaxies in order to obtain an accurate value of
H0 free from the systematic errors associated with "standard
candles." I will review the effect of DE on the Hubble constant and
present the latest MCP results.
- Seminar:
Inhomogeneous cosmology
Who: Dr
Krzysztof Bolejko, Nicolaus Copernius Astronomical
Where: Geoff Opat Seminar Room (360), School of Physics
When:7 Feb 08 at 3:15
Abstract: It
has been widely assumed that the Universe, when viewed on a large enough scale,
is homogeneous and can be described by an FLRW model. The successes of the
Concordance model are built on using a homogeneous background metric combined
with first order perturbation theory. Although this assumption has been
appropriate up to now, and underlies many important developments in cosmology,
it is not the whole story. The Universe as observed is inhomogeneous. Thus if
an homogeneous model if fitted to inhomogeneous Universe values of cosmological
parameters might be incorrectly estimate. Indeed when applying inhomogeneous
and exact solution of the general relativity to cosmology one obtains some new
results. For example it is possible to explain the horizon problem without
employing the inflation. Also assuming existence of ultra-large scale
inhomogeneities (of several gigaparsecs) it is possible to fit supernova data
without the cosmological constant. Whether the observed matter inhomogeneities
can really explain the dark energy or horizon problems still remains an open
question. During my talk I will discuss these and other issues related to
inhomogeneous cosmology.
2007
- Colloquium:
Three Astrophysical Laboratories for Particle Physics
Who: Professor
Avi Loeb, Director of the Institute for Theory and Computation,
Where: Hercus Theatre
When: 19 Dec 07 at 11am-1pm
Abstract: The Universe offers environments with extreme physical conditions that cannot be realized in laboratories on Earth. These environments provide unprecedented tests for extensions of the Standard Model. I will describe three such “astrophysical laboratories:, which are likely to represent new frontiers in cosmology and astrophysics over the next decade. One provides a novel probe of the initial conditions from inflation and the nature of the dark matter, based on 3D mapping of the distribution of cosmic hydrogen through its resonant 21cm line. The second allows to constrain the metric around supermassive black holes based on direct imaging or the detection of gravitational waves. The third involves the acceleration of high energy particles in cosmological shock waves. I will describe past and future observations of these environments and some related theoretical work.
- Public Lecture:
The Past and Future of Our Universe
Who: Professor
Avi Loeb, Director of the Institute for Theory and Computation,
Where: Hercus Theatre
When: 17 Dec 07 at 6:30-7:30pm
Abstract: The initial conditions of our Universe can be summarized
on a single sheet of paper. Yet the Universe is full of complex structures
today, such as stars,galaxies and groups of galaxies. The talk will describe
how complexity first emerged in the form of the first stars out of the simple
initial state of the Universe at early cosmic times.
The future of the Universe is even more surprising. Over
the past decade it was realised that the cosmic expansion has been
accelerating. If this accelerated expansion will continue into the future, then
within a hundred billion years there will be no galaxies left for us to observe
within our horizon except one: the merger product between our own Milky Way
galaxy and its nearest neighbour, the Andromeda galaxy.
For further information on the
sponsors of this lecture please contact Gottfried Lichti via email outcomes@tpg.com.au
Professor Loeb's visit to the
- Colloquium:
Recent Progress in Understanding the Highest Energy Cosmic Rays with the
Pierre Auger Observatory
Who: Professor
Roger Clay, High Energy Astrophysics Group, Department of Physics, The
Where: Hercus Theatre
When:13 Dec 07 at 11am-1pm
Abstract: The
Pierre Auger Observatory is close to completion in western
This colloquium will introduce the observatory and its
physics. Recent results on the arrival directions of these particles will be a
particular focus of the talk.
The most recent publication, plus some discussion, can be
found at: http://www.sciencemag.org/cgi/content/summary/318/5852/896.
- Colloquium:
Doing Physics and Astrophysics with Neutrino Flavor
Who: Professor
Thomas Weiler, Department of Physics and Astronomy,
Where: Hercus Theatre
When:5 Dec 07 at 11am-1pm
Abstract: Estimates of high-energy
astrophysical neutrino fluxes suggest that astro-neutrinos will be detected in
the next few years. Astro-neutrinos bring with them information on the
direction to their source, the energy spectrum of the source, and intrinsic
neutrino-flavor information. We will overview the field of Neutrino Astronomy,
and then discuss how measurements should provide information on source
dynamics, and on neutrino properties including lifetime, mass-matrix, and
cross-section at extreme energy.
- Reionisation and the Lyman-alpha forest
Who: James Bolton, Max Planck Institut für Astrophysik
Where: Geoff Opat Seminar Room
When: 28 Nov 07 at 11am
Abstract: Quasar absorption spectra are currently the premier observational probe of the hydrogen reionisation epoch. The disappearance of the Lyman-alpha forest approaching z=6 indicates the neutral hydrogen fraction in the intergalactic medium (IGM) is increasing with lookback time. However, constraints on the IGM neutral hydrogen fraction atz>6 are still very weak; Lyman-alpha absorption saturates at neutral hydrogen fractions which are still very small - around 1 part in 10^4. Nevertheless, the Lyman-alpha forest can still provide powerful constraints on the metagalactic ionising emissivity at z<6, and by extension the reionisation history at z>6. I shall discuss recent results which indicate reionisation was a rather photon-starved and extended process. At lower redshifts, the Lyman-alpha forest is also a useful probe of the epoch of HeII reionisation, which is thought to coincide with the peak in quasar number density around z=3. I shall present evidence that the observed fluctuations in the HI and HeII Lyman-alpha forest opacity at z<3 are consistent with those expected to arise towards the tail-end of HeII reionisation. I will end with a discussion of radiative transfer effects on the IGM temperature during HeII reionisation, and present some possible evidence that the voids in the IGM at z<3 are significantly hotter than is usually assumed in standard theoretical models of the Lyman-alpha forest.
- Colloquim: Gravitational energy as dark
energy – towards concordance cosmology without Lambda
Who: Professor David
Wiltshire, Department of Physics and Astronomy,
Where: Hercus Theatre
When: 21 Nov 07 at 11am
Abstract: A decade of observations
suggests that the universe is currently undergoing accelerated expansion,
driven by a mysterious vacuum energy or "dark energy" which has been
described by many commentators as the biggest problem in science. In this talk
I will present an alternative, unexpected, explanation for dark energy, purely
within general relativity. Cosmic acceleration is explained quantitatively, as
an apparent effect due to quasilocal gravitational energy differences that
arise in the decoupling of bound systems from the global expansion of the
universe. Although the universe was initially very smooth, today it is very
inhomogeneous on scales less than 200 Mpc, with clusters of galaxies strung in
filaments and bubbles surrounding huge voids. Accounting for spatial curvature
and gravitational energy gradients between galaxies and the volume average
location in voids, leads to a recalibration of average cosmological parameters,
and a rewriting of the standard model of cosmology.
I present a new observationally viable model of the universe, which passes
three key independent cosmological tests - associated with supernovae
distances, the cosmic microwave background (CMB) and galaxy clustering
statistics - and simultaneously resolves particular anomalies, including
primordial lithium abundances and CMB ellipticity. The expansion age is
increased allowing more time for structure formation. Best-fit parameters are
cosmological parameters are presented, including an age of the universe of 14.7
billion years measured in galaxies, a ratio of non-baryonic dark matter to
baryonic matter of 3:1, and a void volume fraction of 76%.
Other unique predictions are made, including a quantifiable variance in the
Hubble flow below the scale of apparent homogeneity, consistent with the
observed "Hubble bubble" feature.
References
[1] D.L. Wiltshire, ``Cosmic clocks, cosmic variance and cosmic averages'',
New J. Phys. 9 (2007) 377 [gr-qc/0702082] [2] D.L. Wiltshire, arxiv:0709.0732
[3] B.M. Leith, S.C.C. Ng and D.L. Wiltshire, arxiv:0709.2535
- Detecting the first quasars
Who: Kirsty Rhook,
Where: Geoff Opat Seminar Room
When: 31 Oct 07 at 3:15pm
Abstract: At intermediate redshifts black hole (BH) growth appears
to be triggered by merging events between galaxies, however the mechanism for
the growth of the first BHs is highly uncertain. Upcoming telescopes promise to
shed light on this era: the next generation of X-ray telescopes have the
potential to detect faint quasars at $z>6$, and the HII regions generated by
accreting supermassive BHs are likely to be the most easily detectable sources
by future 21cm experiments. I will explore various physically motivated models
for BH growth at high redshift which reproduce the low redshift constraints,
and examine the prospects for detecting very high redshift BHs with via their
X-ray emission and 21cm signature.
- Intergalactic metals at high redshift
Who: Dr Emma Ryan-Weber
Where: Geoff Opat Seminar Room, University of Cambridge
When: 18 Oct 07 at 4pm
Abstract: It is quite remarkable that less than a billion years
after the big bang, metals are observed in the intergalactic medium. For metals
to be present, widespread star formation must have occurred at redshifts
greater than 8. Observing these metals comes with its own set of challenges,
since near-Infrared spectroscopy of faint high redshift quasars is required.
During this seminar I will discuss our successful search for Carbon in the IGM
at z~6, together with its implications for the cosmic star formation rate at
high redshift, the epoch of reionization, and the role of galactic winds in the
Lambda-CMD paradigm.
- Modern Cosmology and the Building Blocks of
the Universe
Who: Prof Mark Trodden, Department of Physics,
Where: Laby Theatre
When: 17 Oct 07 at 6:30pm
Abstract: Mark Trodden is Professor of
Physics at
- Dark Matter and Highest Redshift Galaxies:
Seeing the Invisible with Gravitational Lensing
Who: Dr Marusa Bradac, UC
Where: Opat Seminar Room
When: 4 Oct 07 at 4:30pm
Abstract: The cluster of galaxies 1E0657-56 has been the subject of
intense ongoing research in the last few years. This system is remarkably well-suited to
addressing outstanding issues in both cosmology and fundamental physics. It is
one of the hottest and most luminous X-ray clusters known and is unique in
being a major supersonic cluster merger occurring nearly in the plane of the
sky, earning it the nickname "the Bullet Cluster". In this talk I will
present our measurements of the composition of this system, show the evidence
for existence of dark matter, and describe limits that can be placed on the
intrinsic properties of dark matter particles. In addition, I will explain how
this cluster offers a serious challenge to Modified Newtonian Dynamics (MOND)
theories. Finally I will conclude with outlining the plans on using the bullet
cluster as cosmic telescope to explore the Universe in its infancy.
- The Star Formation History of the Universe
Who: Dr Andrew Hopkins, ARC QEII Fellow,
Where: Hercus Theatre
When: 29 Aug 07 at 11:00am
Abstract: The evolution of galaxies in the universe is tightly connected with the rate at which they form stars, and how this quantity evolves with time. Over the past decade a wealth of measurements have been made of the space density of the galaxy star formation rate (a quantity measured in solar masses per year per cubic megaparsec) as a function of time. In particular, strong constraints on this cosmic star formation history (SFH) have recently been established, and a compellingly consistent picture of the SFH has emerged spanning the last 90% of cosmic history. The quantitative normalisation of this SFH is not so well constrained, but we have resolved this problem by using a combination of electron antineutrino flux limits from Super-Kamiokande measurements and supernova rate density measurements. The interesting consequence of this normalisation constraint is a preferred form for the stellar Initial Mass Function (IMF), the distribution of stellar masses produced in a burst of star formation. The IMF is a quantity which is highly likely to have been different in the past, and this can be explored by comparing the evolution of the stellar mass density to the cosmic star formation history. Measurements of these quantities are consistent with each other at the later stages of cosmic history, but systematically and drastically inconsistent at early times. This inconsistency can be resolved by invoking an evolving Initial Mass Function, suggesting that star formation in the early universe was strongly weighted toward more massive stars than at current times.
- Compact Objects as Sources and Detectors of
Gravity Waves
Who: Matthias Vigelius, Postgraduate Student,
Where: Hercus Theatre
When: 24 Aug 07 at 4:15pm
- The Percolating Universe a BillionYears after
the Big Bang
Who: Paul Geil (Postgraduate Student,
Where: Hercus Theatre
When: 24 Aug 07 at 4:15pm
- The Dark
Side of the Universe
Who: Professor Joseph Silk (Department of Physics,
Where: Hercus Theatre
When: 15 Aug 07 at 6:30pm
Abstract: Joseph Silk, Professor of Astronomy at the
- 2006/2007
– An End of Financial year Report on Exoplanets
Who: Professor Chris Tinney (ARC Professorial Fellow, Department of
Astrophysics,
Where: Opat Seminar Room
When: 6 Aug 07 at 2:15pm
Abstract: The last 12 months have been very busy for the study of exoplanets. Spitzer has directly detected an exoplanetary mid-infrared excess; transit searches have detected many more planets, resulting in much more information of exoplanetary radii and densities; and, something like 40 new planets have been reported - some of them allegedly habitable! In addition to continuing its long-running Doppler search for "Solar-system-like" exoplanets, the Anglo-Australian Planet Search has also completed it's first massive chunk of observing as part of a "Rocky Planet Search" for terrestrial-mass planets in short period orbits. With so much going on, its worth having a look back at what's happened over the last 'financial year', and talking about the future directions in which these discoveries are pointing us.
- Hidden
Mass in Cosmic Collisions--- the first pictures of dark matter
Who: Dr
Where: Laby Theatre
When: 27 Jul 07 at 8:00pm
Abstract: The Chandra x-ray telescope has, for the first time, provided sensational images that reveal the dark matter distribution in two colliding galaxies. Dark matter has long been required to explain the way stars orbit inside galaxies and these new images provide additional dramatic confirmation that dark matter exists and behaves differently from ordinary matter. This lecture looks at the implications of this new discovery.
- HuntingDark
Energy from the Optical to the Radio
Who: Dr Chris Blake (
Where: Opat Seminar Room
When: 25 Jul 07 at 2:15pm
Abstract: The dominant component of the physical Universe appears to be a mysterious dark energy whose properties are currently poorly known. Characterizing these properties is one of the most important tasks in cosmology today. Dark energy may signify a breakdown in Einstein's vision of gravity on large scales, or may represent a novel state of matter which can drive acceleration of the cosmic expansion. In this talk I will discuss two Australian-led efforts to solve this problem. I will introduce the "WiggleZ" galaxy redshift survey currently being performed at the Anglo-Australian Telescope, which aims to map the "baryon oscillations" in high-redshift large-scale structure. I will also summarize how the Square Kilometre Array can become the world's premier instrument for cosmological surveys.
- The
Large Hadron Collider – Our Window on the Big Bang
Who: Prof
Geoffrey Taylor (University of Melbourne)
Where: Laby Theatre
When: 6 Jul 07 at 8:00pm
Abstract: On the border of France and Switzerland, an accelerator is nearing
completion that will replicate the conditions that existed shortly after the Big
Bang that started our universe. This lecture looks at the advanced technology
of the accelerator and the fundamental building blocks of nature it will
reveal.
- Stellar Populations of Ultra-Compact Stellar
Systems
Who: Dr Arna Karick (UC Davis/LLNL)
Where: Opat Seminar Room
When: 6 Jun 07 at 2:15pm
Abstract: As part of our Fornax Cluster Spectroscopic Survey
we discovered an intracluster population of ultra-luminous compact stellar
systems. Originally labelled "ultra-compact dwarf galaxies (UCDs), these objects
were thought to be the remnant nuclei of tidally stripped dE,Ns. Subsequent
searches in Fornax using AAT/2dF and VLT/FLAMES have revealed ninety fainter
UCDs, fuelling controversy over their nature and origin. UCDs may be the bright
tail of the globular cluster (GC) population associated with NGC1399.
Alternatively they may be the first spectroscopically confirmed intracluster
GCs, resulting from hierarchical cluster formation and merging in intracluster
space. Determining the stellar populations of these enigmatic objects is
challenging. UCDs are unresolved from the ground but our HST/STIS+ACS imaging
reveals faint halos around the brightest UCDs. In contrast, our recent
Magellan/IMACS and Keck/LRIS+ESI spectroscopy shows that UCDs are unlike GCs and
have intermediate stellar populations with significant variations in their Mg
and Hbeta line strength indices.
- Star
formation and galaxy evolution of
the Local Universe based on HIPASS
Who:Ivy Wong (
Where:Hercus Theatre
When: 4 May 07 at 3:15pm
Abstract: This thesis investigates the star formation and
galaxy evolution of the nearby Local Volume based on Neutral Hydrogen (HI)
studies. A large portion of this thesis consists of work with the Northern
extension of the HI Parkes All Sky Survey (HIPASS). HIPASS is an HI survey of
the entire Southern sky up to a declination of +25.5 degrees (including the
Northern extension) using the Parkes 64-metre radio telescope. I have also
produced a catalogue of the optical counterparts corresponding to the galaxies
found in
- Dwarf
Galaxies and Cosmic Reionization
Who:Dr
Where: Opat Seminar Room
When: 4 Apr 07 at 11:00am
Abstract: Observations of the highest redshift quasars suggest
that hydrogen in the Universe was reionized a billion years after the big bang.
Following this reionization, fluctuations in the distribution of galaxies
contributed to a scatter in the density of ionizing radiation, and hence to
spatial variations in the ionization fraction of cosmic hydrogen on large
scales (tens of Mpc). Simulations predict that the formation of Dwarf galaxies
(with masses less than ~1% of the Milky Way) should have been suppressed after
cosmic hydrogen was reionized, leading to a drop in the rate at which stars
were formed in the Universe. In this talk I will present evidence for this
suppression. In particular I will show that the galaxies which produced most of
the ionizing radiation a few hundred million years after reionization ended,
must have had masses in excess of ~1010 solar masses. This limiting mass is two
orders of magnitude larger than the galaxy mass that is thought to have
dominated the reionization of cosmic hydrogen.
- Gallaxies
by Design
Who: A/Prof.
Where: Opat Seminar Room
When: 15 Mar 07 3:15pm
Abstract: I will present new, multi-purpose, theoretical
models for late-type galaxies. These models comprise a disk, bulge, halo, and
central supermassive blackhole. They represent self-consistent equilibrium
systems and provide clean initial conditions for a wide variety of N-body
experiments. Models designed to match observational data for specific galaxies
are easily found via Bayesian statistics and Markov Chain Monte Carlo. I will
discuss the structure and dynamics of the Milky Way and several other galaxies
as well as a surprising connection between dark halos and the formation of
bars.
2006
1.
TeV Gamma-Ray
Astronomy: Some recent Highlights and Future Plans
Who: Gavin Rowell (University of Adelaide)
Where: Opat Seminar Room
When: 6 Oct 06, 11:00am
Abstract: The past few years have seen a dramatic increase in
the number of TeV gamma ray sources, and with these results, new information
concerning multi-TeV particle acceleration in our Universe. TeV emission is now
established in several types of high energy sources such as shell-type
supernova remmants, pulsar wind nebulae, microquasars and jets in active
galaxies. I will highlight some recent examples and also discuss the concept of
a future ground-based telescope array designed to operate at gamma ray energies
well above 10 TeV. Such an array will probe the origin of Cosmic-Ray
acceleration up to and beyond PeV energies.
- Mileura Widefield Array
Who: Dr Colin Lonsdale (LFD Project Scientist, Haystack Observatory, Massechusetts Institute of
Where: Opat Seminar Room
When: 21 Sep 06 at 11:30am
2005
- Radio-loud AGN Surveys, Black Hole Magnetosphere
Theories, and Sgr A* Variability
Who: Andre Fletcher (SHAO)
Where: Opat Seminar Room
When: 24 September, 3:15
Abstract: It is now believed that supermassive black holes (SMBHs) reside within the centers of most galactic bulges; those galaxies which harbor `Active Galactic Nuclei' (AGNs) may provide us with the more obvious examples of central engines powered by such putative SMBHs. In the period 1990-2005, the speaker has had the opportunity to work on 3 independent projects, each of which is concerned with fundamental questions in this challenging research area, for example:- (1) Where are these `active' SMBHs, in our universe?, (2) How do these SMBH engines work, in astrophysics terms?, and (3) Can we even understand Sagittarius A*, the closest SMBH to us?
Some preliminary results from these ongoing projects are presented, but many questions remain unanswered, and clear insights have been difficult to pin down -- only the surface of these mysteries has been scratched. (This talk in part aims to give a `behind-the-scenes' retrospective look into some of the scientific motivations, chance meetings, and challenges, encountered by the speaker in a personal odyssey spanning 5 countries, and 3 decades). - The distance to the radiogalaxy Centaurus A and
the Thirty Meter Telescope
Who: Professor Jeremy Mould, Director of the National Optical Astronomy Observatory in Tucson, USA
Where: Opat Seminar Room
When: 3:15, September 5
Abstract: NGC 5128's merger with a dwarf galaxy provides it with a generous supply of Cepheid variable stars, which have been used to measure its distance in the same manner as we used to measure the Hubble Constant. The level of participation Australian astronomers are seeking in an Extremely Large Telescope, according to the new decadal survey, is available from the TMT project. An update on TMT is included. - Who: Dr
Bart Pindor,
When:August 3, 3:15pm
Where:Opat Seminar Room
Abstract: - Who: Dr
Peng Oh, UC Santa Barbara
When: July 29, 3:15pm
Where: Opat Seminar Room
Abstract: - A taste of the SCUBA2 future
Who: Dr Doug Johnston, Herzberg Institute of Astrophysics
When: July 22, 10am
Where: Rm 211
Abstract: The problem of star formation is not FORMING stars, but rather NOT forming stars. Indeed, gravitational collapse would proceed quickly in most molecular clouds if not for the addition of non-thermal support mechanisms such as turbulent motions and magnetic fields. Only recently have observations of molecular clouds become sufficient to rigorously test the various theoretical models for cloud support. In this talk I will discuss an ongoing survey, the COMPLETE Survey of Molecular Clouds ( cfa-www.harvard.edu/COMPLETE/ ), and the recent discovery of an extinction threshold for structure formation. I will end the talk with a look at the future of molecular cloud observations in the era of SCUBA2 and HARP at the JCMT, and the arrival of - The NOAO Deep Wide-Field Survey
Who: Dr Michael Brown, Peyton Hall,
When: July 20, 3:15
Where: Opat Seminar Room
Abstract: The NOAO Deep Wide-Field Survey (NDWFS) is a multiwavelength survey designed to study the evolution of galaxies, AGNs, and large-scale structure since $z=5$. The survey consists of two 9 square degree fields imaged with - SKA, Supernova Remnants, Magnetic Fields
Who: Dr Bryan Gaensler,
When: June 16 at 3:15pm
Where: Opat Seminar Room
Abstract: - The Evolution of Super-Massive Black Holes
Who: Dr Scott Croom, Anglo-Australian Observatory
When: June 2nd at 3:15
Where:Opat Seminar Room
Abstract: Super-massive black holes (SMBHs) are now known to be contained in almost all local galaxies. These local SMBHs are generally quiescent. However, in the early Universe SMBHs were extremely active, powering the high luminosity quasars that we at high redshift. The numbers of bright quasars has declined by about two orders of magnitude from the "quasar epoch" at redshift, z~2, to the present. the cause of this evolution is not yet understood. I will show how we can gain some insight into this process, using large surveys of quasars, deep imaging of quasar hosts and theoretical modelling. - What do loose groups tell us about galaxy
formation?
Who: D.J. Pisano,NRC Postdoctoral Fellow
When: April 5th at 3:15
Where: Opat Seminar Room
Abstract: I present the results of a Parkes Multibeam HI survey of six loose groups of galaxies analogous to the Local Group. This survey was sensitive to HI-rich objects in these groups to below 10^7 M(sun) of HI, and was designed to search for low mass, gas-rich satellite galaxies and potential analogs to the high-velocity clouds seen around the Milky Way. This survey detected a total of 79 HI-rich objects associated with the six groups, half of which were new detections. While the survey identified a small number of dwarf galaxies, no star-free HI clouds were discovered. The HI mass function and the mass function of the luminous halos for the six groups are consistent with those for the Local Group. This implies that these groups are true analogs to the Local Group and that the Local Group is not unique in its lack of low-mass dwarf galaxies as compared to the predictions of cold dark matter models of galaxy formation. This survey also constrains the distance to and HI masses of the compact high-velocity clouds (CHVCs) around the Milky Way. The lack of CHVC analog detections implies that they are distributed within <160 kpc of the Milky Way and have average HI masses of <4x10^5 M(sun). The spatial distribution of CHVCs is consistent with the predictions of simulations for dark matter halos. Furthermore the CVDF of Local Group galaxies plus CHVCs matches the predicted CVDF of cold dark matter simulations of galaxy formation. This provides circumstantial evidence that CHVCs may be associated with > low-mass dark matter halos. - Gamma-Ray Bursts and Cosmic Rays: Implications
from Shock Acceleration Theory
Who: Dr. Matthew Baring, Rice University
Where: Opat Seminar Room
When: Wednesday 16th March, 3.15pm
Abstract: The process of diffusive acceleration of charged particles in shocked plasmas is widely invoked in astrophysics to account for the ubiquitous presence of signatures of non-thermal relativistic electrons and ions in the universe. The principal paradigm for gamma-ray bursts suggests that the prompt transient gamma-ray signal arises from multiple shocks internal to a relativistic expansion. This talk summarizes a number of properties of diffusive acceleration at relativistic shocks that pertain to GRB models and the generation of ultra-high energy cosmic rays (UHECRs). Using a standard - Gemini Telescopes Update
Who : Dr Paul Francis
Where: Conference Room
When: Wednesday 9th March 3.15pm
Abstract : These are exciting times at the Gemini Observatories. New capabilities are being commissioned all the time, and planning has begun for a suite of stunning new instruments. The number of nights
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Created: 1999 November 11; Maintained by: F. Hickman; Email: fhickman@isis.ph.unimelb.edu.au