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Previous Seminars
Listed here, in reverse chronological order, are presentations that have
been given recently at the
2009
- Neutron Stars as a Test of Bekenstien's Modified Theory of Gravity
Who: Paul Lasky
(
Where: Geoff Opat Seminar Room 360, School of Physics
When: Wednesday 18 Feb at 3:15pm
Abstract: Modified theories of gravity have had recent success in explaining various phenomena without the need for dark matter or dark energy. Bekenstein's Tensor-Vector-Scalar (TeVeS) theory, which is a relativistic generalization of Milgrom's MOdified Newtonian Dynamics (MOND), has been able to explain gravitational lensing, galaxy rotation curves and the Tully-Fisher relation, and also cosmological observations such as being able to reproduce key features of the CMB power spectra and galaxy distributions. However, these phenomena are manifestations of the theory in the weak gravitational field. In the strong field, various black hole solutions have been discovered, which hint that the structure of spacetime is slightly different near a TeVeS black hole than near a General Relativistic black hole. However, observational evidence of this is extremely difficult to ascertain, and we therefore turn to the study of neutron stars. Using current observations of the masses and radii of neutron stars, we are able to provide independent constraints on the free parameters of the theory, and therefore show a maximum amount that the theory can deviate from General Relativity. Moreover, we predict further constraints on the theory using future observations in the electromagnetic spectrum, as well as with gravitational wave astronomy.
- Progress and Opportunities at the Anglo-Australian Observatory
Who: Andrew Hopkins
(
Where: Geoff Opat Seminar Room 360, School of Physics
When: Thursday 05 Feb at 10:00 am *** NOTE UNUSUAL DAY AND TIME ***
Abstract: Recent developments at our national optical observatory, the Anglo-Australian Observatory, on both scientific and instrumentation fronts will be presented. These include research results from AAO staff, an overview of the ongoing Anglo-Australian Telescope Large Programs (Anglo-Australian Planet Search, WiggleZ - a cosmology survey, GAMA - a galaxy evolution survey), progress on the WFMOS (Wide-Field Multi-Object Spectrograph) concept study, the HERMES (High-Resolution Multi-object Spectrograph) instrument, and a striking demonstration of the OH suppression fibre technology that allows spectroscopy in the near-infrared unaffected by strong night-sky emission lines. Opportunities for students at the AAO will also be highlighted, including PhD top-up scholarships, as well as the currently open Magellan Fellow positions.
2008
- Radio Wave Propagation as a Probe of the Cosmos
Who: Bryan
Gaensler (
Where: Geoff Opat Seminar Room 360, School of Physics
When: 17 Dec 08 at 3:15pm
Abstract: TBA
- Nuclear Astrophysics - current questions and future instrumentation
Who: Cornelia (Trixi) Wunderer (SSL, UC Berkeley)
Where: Geoff Opat Seminar Room 360, School of Physics
When: 10 Dec 08 at 3:15pm
Abstract: Observations of celestial gamma-ray lines constrain the abundance and kinematics of individual isotopes from supernovae, novae, and stellar winds - thus teaching us about nucleosynthesis processes that are part of the cycle of matter in our universe. At the same time, observations of these isotopes, combined with stellar evolution models, constrain the current star formation rate in our galaxy. Recently, INTEGRAL/SPI's measurement of a very unexpected spatial distribution of the 511 keV positron annihilation radiation in our galaxy has turned the question of their origin into one of the most pressing in modern astrophysics. Current instrumentation is not sensitive enough to answer these challenges, and significant advances are awaiting a new generation of instruments. The most viable candidates for a next-generation gamma-ray observatory in the nuclear-line regime are an "Advanced Compton Telescope" providing deep all-sky surveys and a Gamma-ray Lens mission that would focus on a comparatively small number of individual sources.
- A unified description for time variability in pulsars
Who: George
Hobbs (ATNF)
Where: Geoff Opat Seminar Room 360, School of Physics
When: 3 Dec 08 at 3:15pm
Abstract: Based on a new study of pulsar spin-down irregularities and previous observations of an unusual, intermittent pulsar, PSR B1931+24, I present a model for pulsar timing noise. Our model links many pulsar phenomena including moding, nulling, intermittency, pulse shape variability and timing noise. Our model shows that the timing residuals for PSR B1828-11 and its pulse shape variations can be explained, suggesting that this pulsar is not undergoing free precession as previously thought. The ability to model and, hence, remove the timing irregularities leads to the possibility of forming a perfectly stable pulsar clock that could be used to improve tests of general relativity, to search for the elusive gravitational waves and to produce a pulsar-based timescale that, over long time scales, will be competitive with existing terrestrial time scales. In my talk I will describe observations of pulsars over many decades, explain the new model and discuss its implications.
- Surveying the Southern Skies with SkyMapper
Who: Brian
Schmidt (ANU)
Where: Geoff Opat Seminar Room 360, School of Physics
When: 26 Nov 08 at 3:15pm
Abstract: SkyMapper is a 1.3m widefield telescope that is currently being commissioned at Siding Spring Observatory. I will discuss the history of the telescope, its scientific capability, and key science projects for the telescope, which include a survey of 20000 sq degrees of the southern sky, as well as transient searches for supernovae, gamma ray bursts, and even gravitational wave sources. I will also discuss the potential for UniMelb astronomers to access the SkyMapper data stream through collaborative programs.
- Interstellar Ionised Gas: The View from WHAM
Who: Greg Madsen
(
Where: Geoff Opat Seminar Room 360, School of Physics
When: 12 Nov 08 at 3:15pm
Abstract: The interstellar medium (ISM) of the Milky Way is pervaded by an extensive layer of faint, diffuse ionised gas. This low density plasma is a principal component of the ISM and significantly impacts our understanding of the structure and physics of all phases of the ISM. Despite its importance, many questions about the origin, energetics, and physical conditions of the ionised gas remain unanswered. Significant progress has been made through observations from the Wisconsin H-Alpha Mapper (WHAM), a large diameter, high resolution Fabry-Perot spectrograph designed specifically to study extremely faint, diffuse optical emission. WHAM has produced the first spectroscopic sky survey of diffuse ionised gas in the northern Galaxy comparable to all-sky surveys of neutral gas. We have extended the H-Alpha survey work to other diagnostic emission lines; this allows us to characterise the physical conditions of the gas and to compare the results with photoionisation models. The unique capabilities of WHAM have been used to study a range of other phenomena including the Earth's geocorona, the motion of zodiacal dust, large planetary nebulae, high-velocity clouds, and dwarf spheroidal galaxies. In this talk, I will review highlights of WHAM science to date and will discuss ongoing relocation efforts to bring WHAM to the southern hemisphere.
- A curious change in the universe at z=3
Who: John Webb
(UNSW)
Where: Geoff Opat Seminar Room 360, School of Physics
When: 5 Nov 08 at 3:15pm
Abstract:
Spectroscopy of distant quasars probes the evolution of the universe
from about 1Gyr old up to today, 14Gyr after the big bang. New large
astronomical surveys provide samples of unprecedented quality for statistical
analysis. Combining observations of 5875 quasars from the Sloan Digital Sky
Survey with Hubble Space Telescope, Lick and Keck telescope observations, I
will show the highest precision measurements to date for cosmologically
distributed neutral hydrogen over the redshift range 0 Who: Ned Taylor
( Where: Geoff Opat Seminar Room 360, School of Physics When: 29 Oct 08 at 3:15pm Abstract:
Efforts to reproduce the joint color-magnitude distribution of z < 1
galaxies have forced the introduction of some 'quenching' mechanism
that operates to prevent star formation in massive galaxies. In this
talk, I will present the color-magnitude and color-mass diagrams for z
< 2, based on a new, near infrared-selected catalogue of the Extended
Chandra Deep Field South. I will use these data to explore the
existence of the red sequence at z > 1, the color evolution of the red
galaxy population, and the relative number of blue/red (as a proxy for
active/passive) galaxies within the general population of massive,
field galaxies. The data suggest a 'long migration' of massive
galaxies onto the red sequence: at most, 1/5 massive galaxies in the
local universe were already on the red sequence at z ~ 2, while
roughly 1/2 (re)joined the red sequence only after z ~ 1. These
results provide new constraints for models of galaxy formation, and
particularly on the process whereby galaxies are quenched.
Who: Charley
Lineweaver (ANU) Where: Geoff Opat Seminar Room 360, School of Physics When: 15 Oct 08 at 3:15pm Abstract:
If the origin of life and the evolution of observers on a planet is
favoured by atypical properties of a planet's host star, we would
expect our Sun to be atypical with respect to such properties. The Sun
has been described by previous studies as both typical and
atypical. In an effort to reduce this ambiguity and quantify how
typical the Sun is, we identify eleven maximally-independent
properties that have plausible correlations with habitability, and
that have been observed by, or can be derived from, sufficiently
large, currently available and representative stellar surveys. By
comparing solar values for the eleven properties, to the resultant
stellar distributions, we make the most comprehensive comparison of
the Sun to other stars. The two most atypical properties of the Sun
are its mass and orbit. The Sun is more massive than 95 +/- 2% of nearby
stars and its orbit around the Galaxy is less eccentric than 93 +/- 1% of
FGK stars within 40 parsecs. Despite these apparently atypical
properties, a chi2-analysis of the Sun's values for eleven properties,
taken together, yields a solar chi2 = 8.39+/-0.96. If a star is chosen
at random, the probability that it will have a lower value (~ be more
typical) than the Sun, with respect to the eleven properties analysed
here, is only 29+/-11%. These values quantify, and are consistent with,
the idea that the Sun is a typical star. If we have sampled all
reasonable properties associated with habitability, our result
suggests that there are no special requirements for a star to host a
planet with life.
Who: Rick
Perley (NRAO) Where: Podium Room 211, School of Physics When: 7 Oct 08 at 3:30pm Abstract: The Expanded Very Large Array Project is a major upgrade of the Very
Large Array. Begun in 2001, the EVLA Project is now more than 2/3
complete, and is on schedule for completion in 2012. The key goals of
the project are to provide continuous frequency coverage from 1 to 50
GHz with a vastly expanded correlator of remarkable power and
flexibility. In this talk, I will describe the current state of the project, with
emphasis on the newly available frequency bands and expanded tuning
ranges within existing bands -- new capabilities which offer new
science opportunities now. I will show recent results from
commissioning tests of the WIDAR correlator which is now being
installed, and will be available for early science late next year. I
will conclude with a projection of the rapid increase in observational
capabilities, as the full receiver suite and the WIDAR correlator come
on line. Who: Bill
Harris (McMaster) Where: Geoff Opat Seminar Room 360, School of Physics When: 8 Oct 08 at 3:15pm Abstract:
The unparalled imaging capability of HST allows us to carry out
direct star-by-star analysis for huge statistical samples of stars
in nearby galaxies. I will discuss new results for four large
E galaxies including M32, NGC 5128, and the Leo ellipticals which
show a remarkable variety in their star-forming history. These studies
also hint that large galaxies in general may have an ultra-extended,
low-metallicity "outermost halo" that might be the remnant of the
very first stars in their extended dark-matter halo. Who: Prof Bob
Carswell (IoA, Where: Room 760, School of Physics When: 19 Sep 08 at 11:30am Abstract: The heating/cooling balance
in a gas effectively determines its temperature. Observationally temperatures
have normally been determined by measuring excitation of atomic or molecular
energy levels, though radiative mechanisms are often important and these affect
the results. In some cases, however, it is possible to infer temperatures more
directly by measuring the Doppler widths of spectral lines. The results from
these methods using measurements of different atoms and molecules in quasar
absorption spectra are compared, and some significant differences are found. In
particular, the neutral hydrogen 21cm spin temperature favoured by some may not
give the true temperature for any constituent. We confirm that neutral carbon
excitation is dominated by radiative effects, and a choice of the lower
molecular hydrogen excitation levels probably gives reliable kinetic
temperatures in cool (a few 100K) regions. The prospects for investigating the
high redshift analogues of the warm (10000K) regions found in the Galaxy are
less encouraging. Who: Duncan
Galloway ( Where: Geoff Opat Seminar Room 360, School of Physics When: 10 Sep 08 at 3:15pm Abstract: Thirty years of
observations of thermonuclear (type-I) bursts from accreting neutron stars have
revealed a surprisingly rich spectrum of behavior. A few sources which have
been studied intensively offer confirmed examples of the three classes of
ignition predicted theoretically, and these systems serve as crucial test-cases
for numerical models. However, the behavior of the majority of systems cannot
be fully reconciled with theoretical predictions, suggesting there is
additional physics at work. I will present recent results from analysis of the
combined public observations made by the Rossi X- ray Timing Explorer (RXTE)
over more than 10 years, totalling 1185 bursts from 48 sources. The two most
prolific bursters in the sample exhibit distinctly different bursting
properties, suggesting different accreted compositions in the accreted fuel,
and highlighting the diversity in burst behaviour which must be considered when
combining burst samples. I will also describe a successor project, the
Multi-Instrument Burst ARchive (MINBAR), which aims to collate all bursts
observed by modern instruments to enable comprehensive future studies of rare
events and broad-scale behaviour. Finally, I will describe some of the
approaches we are using to try to constrain the neutron star equation-of-state
via thermonuclear burst measurements as part of these studies. Who: Gary Da
Costa (ANU) Where: Geoff Opat Seminar Room 360, School of Physics When: Fri 5 Sep 08 at 11:30am **NOTE UNUSUAL DAY AND TIME Abstract: The results of a spectroscopic
search with the AAT's 2dF multi-fibre spectrograph for candidate members of the
unusual globular cluster Omega Centauri at and beyond the cluster tidal radius
will be presented. Both radial velocity and line strength information is used
to identify possible candidate members. The outcome is a limit on the fraction
of the total cluster mass contained in the region between 1 and 2 cluster tidal
radii, and will be discussed in the context of theories which postulate that
Omega Centauri is the remnant nucleus of a tidally disrupted dwarf galaxy. 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. 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 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. 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. 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 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. 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. 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. 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. 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. Who: Where: Geoff Opat Seminar Room 360, School of Physics When: 8 May 08 at 3:15pm Abstract: TBA 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. 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. 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. 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. 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. 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 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. 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. 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. 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 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. 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. 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 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. 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. Who: Matthias Vigelius, Postgraduate Student, Where: Hercus Theatre When: 24 Aug 07 at 4:15pm Who: Paul Geil (Postgraduate Student, Where: Hercus Theatre When: 24 Aug 07 at 4:15pm 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 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. 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. 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. Who: Prof
Geoffrey Taylor (University of Melbourne) Who: Dr Arna Karick (UC Davis/LLNL) Who:Ivy Wong ( Who:Dr Who: A/Prof. 1.
TeV Gamma-Ray
Astronomy: Some recent Highlights and Future Plans [Home] [Contacts] [Research] [Study] [Events] [Local] [Data Centre] [Astronomy Central] © The University of Melbourne 1994-2000. Disclaimer and Copyright
Information. Authorised by: Head of Astrophysics Group, School of Physics
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.
2007
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.
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.
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
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.
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
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.
Who: Dr Colin Lonsdale (LFD Project
Scientist, Haystack Observatory, Massechusetts Institute of
Where: Opat Seminar Room
When: 21 Sep 06 at 11:30am
2005
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).
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.
When:August 3, 3:15pm
Where:Opat Seminar Room
Abstract:
When: July 29, 3:15pm
Where: Opat Seminar Room
Abstract:
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
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
Who: Dr Bryan Gaensler,
When: June 16 at 3:15pm
Where: Opat Seminar Room
Abstract:
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.
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.
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
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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Last modified: ;
Created: 1999 November 11; Maintained by: F. Hickman; Email: fhickman@isis.ph.unimelb.edu.au