For more information on colloquia at the Centre for Astrophysics and
Supercomputing please contact Dr. Nikole Nielsen ()
Dec 16th 2009 (Wednesday) @ 11:30am
(CfA, Harvard University)
Lyman Alpha Nebulae as an Observational Signature of Cold
Accretion onto Galaxies
Hydrodynamical simulations of galaxy formation reveal streams
of cold (T~1e4 K) gas into the centers of dark matter halos as massive as
1e12-1e13 solar masses at redshifts between 1 and 3. I show that if > 20%
of the binding energy of this cold gas is radiated away, then the simulated
cold streams are spatially extended Lyman alpha (Lya) sources with
luminosities, Lya line widths, and number densities that are comparable to
those of observed Lyman Alpha nebulae, a.k.a `blobs'. The filamentary
structure of the cold flows can explain a wide range of Lya blob
morphologies. Since in CDM the most massive halos form in dense
environments, the observed association of Lya blobs with overdense regions
arises naturally. I argue that Lya blobs--even those that are clearly associated with starburst galaxies or quasars-- provide the first direct
observational support for the cold accretion mode of galaxies. I discuss
testable predictions and weaknesses of this model.
Dec 15th 2009 (Tuesday) @ **10:30am**
(Liverpool John Moores)
ACS Coma Cluster Treasury Survey: Velocity dispersions of cluster galaxies from Keck/DEIMOS spectra
The core of the Coma Cluster offers a unique laboratory for testing models of galaxy formation. The presence of not one but two cD
galaxies, large-scale stellar streams, intergalactic diffuse optical light, and X-ray wakes produced by infalling subclusters attest to
Coma being one of the most extreme environments in the low-redshift universe. The HST/ACS Coma Cluster Treasury Survey aims to address many outstanding issues concerning galaxy formation and provides a fundamental low-redshift reference and comparison for cluster studies at high redshift. I will present our survey strategy and briefly describe the publicly available catalogue of basic structural properties. I will also present velocity dispersions for ~40 cluster dwarf galaxies, identified in the ACS imaging and observed using the Keck/DEIMOS spectrograph. Combined with accurate structural information, the velocity dispersions facilitate a detailed analysis of the fundamental galaxy "scaling laws", and by inference their dark matter content. These observations help constrain galaxy formation models and provide further insight into their formation and evolution in dense environments.
Dec 10th 2009 @ 11:30am
(CfA, Harvard University)
Cold mode of gas accretion
Most galaxies are actively star forming at all epochs. However,
observations of cold gas reservoirs indicate that, at any epoch, there
is not enough gas in dense galactic component to support evolution of
star formation activity over time. This suggests that galactic gas is
being replenished from the intergalactic medium.
I use fully cosmological simulations of galaxy
formation to study the gas supply into galactic component from high
redshift to present. At high redshift infall of cold
filamentary gas dominates the gas supply of all galaxies. This "cold
mode accretion" is a major driver of very active star formation
of high-z galaxies enabling such activity to proceed for a significant
fraction of the Hubble time. Properties and geometry of infalling gas
change with halo mass and redshift. At low redshift some of the halos are
able to cool hot virialized gas but filaments are still indirectly
supplying galaxies with
gas via cold gaseous clouds that form from infaling cold/warm filamentary
gas. In this talk I will describe properties, physics and consequences
of such gas accretion for the formation and evolution of galaxies.
Finally, I will point out promising directions for
future research in this area and discuss several observational probes
of cold halo gas that can provide strong constraints on the physics of
gas accretion in galaxies.
Dec 8th 2009 (Tuesday) @ 11:30am
(Queen's University, Canada)
I review the status of measurements of galaxy baryonic and dark
matter masses. Whether the mass modeling techniques that I will
discuss are applied to gas-rich or gas-poor galaxies, uncertainties
can be large. Yet, despite these large internal errors, a common
picture for the distribution of baryonic mass in galaxies emerges.
Dec 3rd 2009 @ 11:30am
Starting Reionization with the First Stars and Galaxies
The first stars are thought to be extremely luminous and reside in dark matter halos with masses of approximately a million solar masses. I will present results from radiation hydrodynamics simulations that follow the formation of tens of metal-free stars and their impact on high-redshift galaxy formation and reionization. HII regions created by the first stars are a few kiloparsecs in radius, which then overlap with each other and constitute a volume filling fraction of about a quarter at redshift 15. Our simulations also include pair-instability supernovae and the ensuing chemical enrichment of the IGM and subsequent star formation. We find that the first galaxies are enriched up to 1/1000th of solar metallicity, which is sufficient to transition to lower-mass star formation. The escape fraction in such
galaxies always exceeds 0.25 and can reach up to 0.8 in some cases.
Nov 26th 2009 @ 11:30am
Serena Bertone (University of California at Santa Cruz)
Title: The metal line
emission of the intergalactic medium in OWLS
I will discuss the possibility to detect the
intergalactic medium at different redshift through metal line
emission. The diffuse intergalactic gas accounts for most of the
baryonic mass in t he universe, but is extremely difficult to
detect. A number of instruments are being planned to detect emission
from the missing baryons, both in the local and in the distant
universe, in wa velengths spanning from the optical to the X-rays. I
use OWLS, a new suite of hydrodynamical simulations of structure
formation that includes a la rge number of runs with varying physical
prescriptions for star formation, feedback, cooling an d several other
physical processes, to predict the intensity of the emitted flux in a
sample of X-ray and UV emission lines at low redshift and in a sample
of redshifted rest-frame UV emissi on lines at z>2. At high redshift a
number of lines, among others C III, C IV and O VI, should be
detectable in relatively high density regions by upcoming optical
instruments such as the Co smic Web Imager.
Nov 24th 2009 @ **11:00am**
ELT: the Emperor's Large Telescope?
Access to Extremely Large Telescopes with apertures greater than 20m is at the top of Australia's Decadal Plan wishlist for optical astronomy. Despite this, there has been relatively little public debate of the technical issues and no presentations (that I am aware of) locally detailing the architectures and trade-offs for these new generation telescopes. Do these projects offer value for money? Do the three major competitor projects all offer similar capabilities and risks? What are ELT's likely strengths and weaknesses? In this talk, I present a grad-student level overview of some of the main issues with the primary aim of sparking further and more widespread community engagement with this critical component of our future optical facilities.
There will be a 30 minutes discussion session afterwards for those interested.
Nov 19th 2009 @ 11:30am
Analytic and numerical realisations of a disk galaxy
Recent focus on the importance of cold, unshocked gas accretion in galaxy
formation (not explicitly included in semi-analytic studies) motivates a
detailed comparison between two inherently different modelling techniques:
direct hydrodynamical simulation and semi-analytic modelling. By analysing
the physical assumptions built into the "gasoline" simulation, formulae for
the emergent behaviour are derived which allow immediate and accurate
translation of these assumptions to the "galform" semi-analytic model. The
simulated halo merger history is then extracted and evolved using these
equivalent equations, predicting a strikingly similar galactic system. This
exercise demonstrates that it is the initial conditions and physical
assumptions which are responsible for the predicted evolution, not the
choice of modelling technique. On this level playing field, a previously
published galform model is applied (including additional physics such as
chemical enrichment and feedback from active galactic nuclei) which leads to
starkly different predictions.
Nov 18th @ 11:30am
Exploring The Time Domain With Synoptic Sky Surveys
Time-domain astronomy is rapidly becoming an exciting new research frontier, touching on fields ranging from studies of the Solar system, to cosmology and extreme relativistic astrophysics. A new generation of digital synoptic sky surveys is now creating Terascale data streams, and moving rapidly into the Petascale regime. We will describe briefly some of the ongoing studies based on the Palomar-Quest survey and Catalina Real-Time Transient Survey, and some of the computational challenges, focusing on the automated classification of transient events and their follow-up.
Nov 17th 2009 @ **2pm**
Fundamentals of Supernova Cosmology
Since the surprising discovery of cosmic acceleration in 1998,
subsequent observations of the cosmic microwave background and the
large-scale distribution of galaxies have converged on a picture in
which the universe has ~2/3 dark energy and ~1/3 dark matter.
Ordinary baryons, lost in the round-off error, are only about 4% of
the mass-energy in the universe. Over the past decade, larger samples
of supernovae have made the existence of this negative-pressure
component of the universe more secure. Now our effort has shifted to
determining the properties of the dark energy. Alas, theory has
nothing much to offer as a plausible hypothesis to test. One simple
question seems worth answering: "Is dark energy a constant, like a
modern version of Einstein's cosmological constant, or has it changed
over cosmic time?" Supernova samples are now large enough that
systematic errors dominate over statistical uncertainties, so better
understanding, not just a larger sample, is required to make progress
on this question. The largest systematic errors in supernova
distances come from the pernicious effects of interstellar dust
absorption. New observations carried out at near-infrared wavelengths
promise to reduce these errors and lead to a more certain knowledge of
the nature of dark energy. This talk will sketch the present
constraints on dark energy, illustrate how these can be improved with
near-infrared measurements of supernovae, and speculate on the best
strategy for future measurements with the proposed Joint Dark Energy
Nov 12th 2009 @ 11:30am
The effect of environment on the neutral gas content of galaxies
I will discuss the effect that environment plays on the neutral
hydrogen content of galaxies. In particular, I will report on GEMS, a
multi-wavelength study of 16 galaxy groups, for which we have optical,
HI and X-ray mapping. This allows us a unique view of both the hot and
cold gas in the group environment. When combined with information on
the dynamics and evolutionary state of the groups, we can begin to
form a picture of how the group environment influences the evolution
of its member galaxies. I will discuss the stripping of gas from
galaxies in groups, including likely ways to strip gas, and the
existence of HI-deficient galaxies in the group environment. The HI
mass function for groups will be presented, and I will also report on
intra-group HI and discuss likely origins for such gas. To conclude, I
will describe how the upcoming ASKAP will further progress this field
Nov 5th 2009 @ 11:30am
Probing Large-Scale Structure with Radio Observations
Observations of diffuse synchrotron emission in large-scale
structure have the potential to address key issues such as the
cosmological origin of magnetic fields, the physics of cosmic-ray
acceleration, and the detection and characterization of the elusive
warm-hot intergalactic medium (WHIM). I will present current efforts to
detect synchrotron signatures of large-scale structure formation,
emphasizing the principal observational obstacles and limitations. I will
then outline the major advances that will be possible with the next
generation of radio telescope arrays.
Oct 29th 2009 @ 11:30am
Sub-AU imaging of turbulent structures in the Interstellar Medium
Turbulence in the ionized Interstellar Medium (ISM) of our Galaxy scatters the radio emission of some pulsars so heavily that their radiation undergoes multipath propagation, so that their scattered images contain thousands of sub-images, or speckles, of the pulsar. We have developed a technique to construct the first-ever speckle image of a highly scattered pulsar. This probes the underlying magneto-hydrodynamic turbulence of the ISM on scales ~0.01 to 20 AU and has revealed several unexpected features. The most striking is the presence of a highly inhomogeneous object located ~10AU off-axis whose properties are consistent with an Extreme Scattering Event (ESE) cloud. ESE clouds are also implicated in large (10-50%), one-off flux density excursions of some radio quasars. Their existence is problematic because the electron densities implied by simple models require the clouds to be ~10^3 times overpressured with respect to the ambient ISM; such clouds would appear be very short-lived and much less prevalent than is observed. We discuss the properties of ESE clouds as revealed by our observations. We also discuss the relevance of similar off-axis clouds to precision pulsar timing arrays, especially those trying to detect gravitational radiation.
Oct 22nd 2009 @ 11:30am
(University of Tasmania)
How GASKAP will change our understanding of galaxy evolution
The Galactic Australian Square Kilometre Array Pathfinder (GASKAP) survey will be a wide-area study of the 21 and 18-cm lines of H and OH in the interstellar and circumstellar media of the Milky Way (MW) and the Magellanic Clouds (MC's). The area to be covered includes the thin and thick disks of the MW south of declination +40 deg, the MC's along with the Magellanic Bridge and Stream, and a few other fields of particular interest. A broad range of science goals will be achieved; the most profound is to understand how galaxies evolve as star formation progresses, by measuring the rates of mass loss and accretion, chemical enrichment, and energy and momentum balance between the disk and halo.
Oct 15th 2009 @ 11:30am
(NCRA, TIFR and ATNF, CSIRO)
Environments and evolution of Radio galaxies
Radio galaxies and quasars, which are amongst the most
luminous and largest single objects in the Universe, range
in size from less than a few tens of pc to over several
Mpc. They continue to pose a wide range of interesting
astrophysical questions. We will initially focus on the small sources which are of sub-galactic dimensions, and explore possible evidence of interactions of the jets with gas clouds via both total-intensity and polarization observations. Some of these gas clouds may be fuelling the
radio source. We discuss the HI properties of these compact sources, and also examine whether these are consistent with the unified scheme for radio galaxies and quasars. One of the interesting questions related to radio galaxies and quasars is whether their AGN activity is episodic and if so, the range of times scales of such activity. We discuss some of the physical properties of large radio galaxies, focussing on those which show signs of episodic activity.
Oct 14th 2009 (Wednesday) @ **3:30pm**
(Univ of Sydney)
ELT: the Emperor's Large Telescope?
Access to Extremely Large Telescopes with apertures greater than
20m is at the top of Australia's Decadal Plan wishlist for optical
astronomy. Despite this, there has been relatively little public
debate of the technical issues and no presentations (that I am aware
of) locally detailing the architectures and trade-offs for these
new generation telescopes. Do these projects offer value for money?
Do the three major competitor projects all offer similar capabilities
and risks? What are ELT's likely strengths and weaknesses? In this
talk, I present a grad-student level overview of some of the main
issues with the primary aim of sparking further and more widespread
community engagement with this critical component of our future
(This is a joint AAO/ATNF Astrophysics Colloquium and we'd be joining via video conference from the CAS meeting room AR101b).
Oct 9th 2009 (Friday) @ 11:30am
Galaxy clusters as a dark energy probe
Galaxy clusters are the most massive virialised structures in the
Universe. Their number density depends on both the geometry of the
Universe and the rate at which structure grows.
Galaxy clusters are also rich in relatively dust-free, early-type
galaxies, which are known to host only Type Ia supernovae. Evidence
from several surveys now suggest that Type Ia supernovae hosted by
early-type galaxies are better standard candles than Type Ia
supernovae hosted by galaxies of other types.
In this talk I will describe how clusters can be used as a dark energy
probe, both through the number density of clusters and the through the
Type Ia supernovae that can be found in them.
Oct 8th 2009 @ 11:30am
Milliarcsecond resolution radio "surveys" to shed light on galactic evolution
Sensitive radio surveys are beginning to make
substantial contributions to deep, multiwavelength fields and detect
many galaxies at high redshift. This situation will accelerate with
the completion of new arrays such as ASKAP and upgrades such as CABB
at the ATCA and the EVLA. All of this new information, however, is
provided by km-scale interferometers, and hence lacks the resolution
to distinguish radio sources powered by nuclear starbursts from those
powered by AGN (and of course the inevitable hybrids). With its
extremely high angular resolution, Very Long Baseline Interferometry
is a natural way to address this problem, filtering out all emission
except originating in AGN. However, the paltry fields of view
(several arcseconds) available to traditional VLBI has hampered its
usability. In this talk, I will describe a novel means of
circumventing this limitation and observing hundreds of radio sources
at VLBI resolution per primary beam (tens of arcminutes), and its
application to current galaxy evolution studies in the Chandra Deep
Oct 1st 2009 @ 11:30am
(Australian National University)
Searching for Southern Transiting Planets
While there have been over 370 extrasolar planets discovered, only 60 of these transit in front of their host star. These transiting planets are very important, as they alone allow us to study a wide range of planetary properties, ranging from bulk density to temperature to atmospheric composition. The majority of transiting planets have been detected in the northern hemisphere, primarily by groups using dedicated, small aperture telescopes.
I will discuss two projects aimed at finding transiting planets in the southern hemisphere. The first of these is the SuperLupus project, a long-duration transit search close to the Galactic Plane. This project is now complete, and we found that the rate of Hot Jupiter planets around Galactic field stars is lower than previously estimated (0.3% rather than 1%). The second project is the HAT-South project, which is a global network of small aperture, wide-field telescopes. One of the three network sites for this project is Siding Spring Observatory.
Sep 25th 2009 @ 11:30am
(IoA, Cambridge University)
Is all motion Relative?
Newton's invention of Absolute Space was essential for the
development of Dynamics but Leibniz and later Mach rejected it.
Einstein showed it was not absolute but did not remove the infuence
of space on mechanics completely. We first give a truly relative
classical mechanics which is in exact agreement with Newton's in
our non-rotating universe. We then demonstate that General
Relativity gives all the main Machian effects and conclude that only
spaces closed by the mass of the energy they contain obey Mach's
precepts. Other solutions of Einstein's equations do not obey his
boundary conditions and may be considered unphysical.
Sep 24th 2009 @ 11:30am
Revealing the Invisibles: the Stromlo Missing Satellites Survey
Over the last few years, systematic searches of Sloan Digital Sky Survey (SDSS) data have discovered
many ultra-faint dwarf galaxies orbiting the Milky Way, bracing the notion from Cold Dark Matter theory
that substantial numbers of Milky Way satellites still remain undetected. The median total luminosity of this
previously unseen class of galaxies is only M_V ~ -4, fainter than the luminosity of a typical Milky Way globular cluster.
It is these least luminous and highly elusive aggregates of shining baryons that hold the greatest leverage in
constraining dark matter and galaxy formation models.
After an overview of this research field I will talk about the latest activities of the Stromlo Missing Satellites Survey team,
two imaging campaigns conducted at the Subaru/Magellan telescopes aimed at revealing the true nature of 11 newly
detected ultra-faint Milky Way satellite candidates. The diversity of findings provide the wanted empirical input necessary
to speculate about what lies ahead and when we will possibly reach the bottom of the barrel.
Sep 18th 2009 (Friday) @ 11:30am
Wide Field Transient Surveys
The time domain of the radio wavelength sky has been only sparsely explored.
Nevertheless, recent discoveries from limited surveys and serendipitous
discoveries indicate that there is much to be found on timescales from
nanoseconds to years and at wavelengths from meters to millimeters. These
observations have revealed unexpected phenonmena such as rotating radio
transients and coherent pulses from brown dwarfs. Additionally, archival
studies have revealed an unknown class of radio transients without radio,
optical, or high-energy hosts. The current generation of new
centimeter-wave radio telescopes such as the ATA, SKAMP, and ASKAP will
exploit wide fields of view and flexible digital signal processing to
systematically explore radio transient parameter space, as well as
lay the scientific and technical foundation for the SKA. Known unknowns that
will be the target of future transient surveys include orphan gamma-ray burst
afterglows, radio supernovae, tidally-disrupted stars, flare stars,
and magnetars. While proving the variable sky, these surveys will also
provide unprecedented information on the static radio sky.
I will present results from three ATA surveys: the Fly's
Eye survey, the ATA Twenty CM Survey (ATATS), and the Pi GHz Survey (PiGSS).
Sep 10th 2009 @ 11:30am
A multiwavelength analysis of Blue Compact Dwarf Galaxies
Blue compact dwarf galaxies (BCDGs) represent the subset of low-luminosity galaxies undergoing a strong and short-lived episode of star formation at the present time. We are obtaining deep multiwavelength data of a sample of nearby BCDGs combining broad-band optical/NIR and Halpha photometry, optical spectroscopy and 21-cm radio observations in order to understand their chemical and physical properties, star formation activity, kinematics, estimate the importance of the young/old stellar populations within them and the environment in which they reside. Indeed, some of the chosen BCDGs are in galaxy groups, but others are apparently isolated. In this talk, I will compare the results obtained for BCDGs both located in galaxy groups and found isolated. I will remark the evident interaction features that all of them show in their neutral gas component. I will remark on the apparent rotation of the HI component about the optical major axis of NGC 5253 (Lopez-Sanchez et al. 2008a; data from the "Local Volume HI Survey" -LVHIS- project), the complex neutral gas morphology and kinematics found in Tol 9 (Lopez-Sanchez et al. 2008b), the prominent HI tidal tails and detached HI cloud found in Tol 30, a long HI bridge between two galaxies in Tol 1924-416, and the huge and disturbed HI content of the NGC 1512 / NGC 1510 system (Koribalski & Lopez-Sanchez, 2009; data also from the LVHIS project). This analysis strongly suggests that interactions with or between low-luminosity dwarf galaxies or HI clouds are the main trigger mechanism of the star-forming bursts in BCDGs; however these dwarf objects are only detected when deep optical images and complementary HI observations are performed.
Sep 4th (Friday) 2009 @ 11:00am
Keck constraint on the variation of the proton-to-electron mass ratio at high redshift
Sep 3rd 2009 @ 11:30am
Revealing Elliptical Galaxy Halos
Halos contain most of a galaxy's mass but they are poorly probed. Individual elliptical galaxy masses are
difficult to measure. Here I discuss a new technique to probe galaxy halos and measure elliptical galaxy masses.
The technique is illustrated with data from the Deimos spectrograph on Keck. Initial results and some galaxy formation model predictions are described. Finally a new survey called GHOST is presented.
Aug 28th (Friday) 2009 @ 11:30am
Inefficient star formation: the combined effects of magnetic fields and radiative feedback
I will discuss our recent addition of physics to simulations of star cluster formation which have previously relied only on pure hydrodynamics with a mock equation of state and self-gravity. In particular we consider the role of magnetic fields and radiative heating of the gas surrounding newborn protostars on the star formation process. The simulations as a result show much better agreement with observations of nearby star forming regions in our Galaxy, especially with respect to the efficiency with which gas is converted into stars, observed to be around ~ 3-6% per free-fall time. Other problems such as an overproduction of low mass stars and brown dwarfs in the models with respect to observations also appear to be resolved by the improved physics.
Aug 24th 2009 @ 15:00 (note unusual time)
My Work with Carl Sagan
A description of 25 years of close collaboration between Jon Lomberg and the most famous astronomer of the 20th Century. Illustrated with artwork and animation from the TV series COSMOS, the movie CONTACT, Nuclear Winter, and NASA's Voyager Record. Their collaboration is a prime example of how to communicate science effectively to the public.
Aug 20th 2009 @ 11:30am
Galaxy Assembly and Cosmology on Our Doorstep
In hierarchical scenarios, large galaxies like the Milky Way and M31 form via the merger and accretion of smaller systems, and evidence of these processes can be found in the stellar streams and the surviving satellites surrounding each galaxy. The advent of large-area astronomical surveys like the Sloan Digital Sky Survey (SDSS) has revolutionised our ability to find and study Local Group stellar structures at unprecedentedly faint surface brightnesses, and these capabilities are expanding, with numerous projects now underway or starting in the next few years. I will give an overview of the flood of recent stream and satellite discoveries in the Local Group made with data from SDSS and other surveys, and present the results of detailed follow-up observations with both ground- and space-based telescopes. These new discoveries are already providing important constraints for models of galaxy formation, as well as yielding clues to the behaviour of dark matter on the smallest scales. In coming years, the symbiotic evolution of observational resources and theoretical models will lead to a new understanding of the processes involved in galaxy formation in the Local Group -- and by inference, the Universe.
Aug 19th 2009 @ 11:30am
(University of Queensland and University of Copenhagen)
Using cosmology to test fundamental physics
One of the most exciting outcomes of the last decade of astrophysics is the realisation by the wider physics community that cosmology has bearing on new theories of fundamental physics. This has been driven by the discovery of the accelerating universe --- the theories being proposed to explain dark energy often invoke new physics such as brane-worlds arising from fledgling models of quantum-gravity. It has become evident that the large timescales and spatial-scales probed by cosmology allow us to learn about fundamental physics in a way inaccessible to any earth-bound experiment.
This talk will review my work as part of the ESSENCE and SDSS supernova surveys, and the WiggleZ Baryon Acoustic Oscillation survey, to test new fundamental physics. I'll present the latest SDSS data that is about to be released and discuss how the cosmological constraints will be improved in the future with more data, different types of data, and improved analysis techniques.
Aug 3-15th 2009
IAU General Assembly
Rio de Janeiro
Jul 23rd 2009 @ 11:30am
(University of Lyon, France)
The goal of the “Cosmic Flows” program is to obtain the densest and deepest possible coverage of galaxy distances and, hence, of line-of-sight peculiar velocities. We want to improve the local determination of the Hubble Constant and measure departures from the cosmic expansion that presumably can be attributed to the distribution of matter. We are giving consideration to 7-10 different methods for deriving distances. One of these relies on the correlation between galaxy luminosities and rotation rates, so called Tully-Fisher relation. We have acquired from our own observations and from digital archives, and re-measured more than 16,000 HI spectra, for about 12,500 spiral galaxies in the local universe. I will present the dynamic maps that are currently drawn from this data.
Those cosmic flows lead to a better understanding of the density and distribution of Luminous Matter, Dark Matter, and eventually to the local Dark Energy density.
Jul 16th 2009 @ 11:30am
(European Southern Observatory)
The stellar populations and structure of the Milky Way analogue NGC 891
NGC 891 is an edge-on galaxy that is referred to in the literature as the Milky Way analogue. In this presentation I will give a summary of recent investigations of the thick disk and halo of this galaxy based on deep Hubble Space Telescope ACS observations. Using the star counts we detected the presence of a thick disk component in NGC 891 with vertical scaleheight h_Z = 1.44 +/- 0.03kpc and radial scalelength h_R = 4.8 +/- 0.1kpc, only slightly longer than that of the thin disc. The stellar spheroid, probing the halo population, presents a modest chemical gradient, with the median reaching [Fe/H] ~ -1.3 at r ~ 20kpc. Within the distance of the solar-like radius the metallicity distribution is significantly different with respect to that of the Milky Way. I will argue that we found evidence for significant small-scale variations in the median colour and density in NGC 891 halo, that are most likely due to variations in the stellar metallicity. Their presence suggests that the halo of this galaxy is composed of a large number of incompletely mixed sub-populations, testifying to its past accretion history.
Jul 10th 2009 @ 11:30am
Centaurus A: Interaction between a Radio Source and its Environment
As the nearest extragalactic double radio source, Centaurus
A provides our best chance to study a radio source in action. Deep
new X-ray data is revealing how the radio source deposits energy in
its environment and how the environment affects the morphology of the
Jun 28th - 3rd Jul 2009
Centaurus A meeting
July 2nd 2009 @ 11:30am
The New Picture of Star Formation Histories in Field Galaxies: Towards a Consistent Picture From Observations and Theory
The deepest multi-wavelength surveys now provide measurements of star
formation in galaxies out to z>2, and allow to reconstruct its history
for large parts of the galaxy population. I review recent studies,
which have consistently revealed a picture where galaxy star formation
rates and their evolution are primarily determined by galaxy mass.
Unless they undergo a quenching of their star formation, galaxies of
similar masses have very similar star formation histories, which turn out
to be relatively smooth: star formation rates decline with redshift in a
primarily gradual manner, while typical starburst episodes have only
a modest amplitude that barely evolves.
I discuss how the found relations and their redshift evolution can provide
an observed reference star formation history as a function of galaxy
mass. Such data now serve as a baseline to quantify secondary
parameters that influence star formation.
The observed amplitudes and timescales of galaxy star formation are
not fully reproduced by current theoretical models, and are a
promising testbed to improve the assumed baryon physics. However,
measurements of star formation rates in distant galaxies need to be
treated with caution. I give an outlook of new data, methods and instruments that will help us to
improve our understanding of high redshift star formation.
Jun 30th 2009 @ 11:30am
Galaxy Evolution in Rich Environments
By combining multi-wavelength observations of galaxies spanning the
range in redshift and environment, we can identify the physical
mechanisms and timescales for transforming the field population into
the passive early-type galaxies that dominate local clusters. I will
summarize our recent work showing that 1) the most massive galaxies in
groups and clusters can form at z<1 via dissipationless merging; 2)
dusty star formation is enhanced in galaxy groups at intermediate
redshifts; and 3) there is an increasing fraction of dust-obscurred
star formation with increasing redshift in galaxy clusters (0
Jun 29th 2009 @ 2pm
Demystifying the Gemini Queue (via video conference)
Dr Henry Lee will cover the following topics, amongst others:
- How the Gemini queue works
- Using Observing Condition constraints to your advantage
- Frequently-made mistakes in Phase 2 preparation
The format will be a presentation by Henry followed by a moderated question and answer session.
We'll be connecting to the Australian Gemini Office from the Meeting Room at CAS.
Jun 25th 2009 @ 11:30am
Galactic Genealogy: Chemical Similarities between the Galactic Bulge and Local Thick Disk Red Giant Stars
The formation and evolution of the Galactic bulge and its relationship with the other Galactic components is still poorly understood. To establish the chemical differences and similarities between the various populations, we present a homogeneous and differential elemental abundance analysis of bulge giant stars and halo, thin- and thick-disk high quality optical and near-infrared spectra of red giant stars in the solar neighborhood. In this talk, I will present the outcomes of this project, which reveal new clues about the chemical enrichment history of the Galactic bulge and thick disk.
Jun 19th 2009 @ 11:30am
(Institut d'astrophysique de Paris)
Exploring the recent star formation history of galaxies
The field of galaxy evolution has made enormous progress in
the last two decades, to a large extent thanks to optical
spectroscopic galaxy surveys. I will start by reviewing the physical
information that allows us to extract star formation histories from optical spectra.
I will then present some recent work on the role of gas-rich major mergers in the build-up of the red sequence since z~0.7, on the unspectacular recent star formation history of local AGN hosts, and the quenching mechanisms in SDSS clusters.
Jun 18th 2009 @ 11:30am
The Large-Scale Environments of Type Ia Supernovae
Both as high-energy astrophysical phenomena and as cosmological probes,
type Ia supernovae are critical to our understanding of galaxy
evolution. For instance, feedback from supernovae directly influences
star-formation histories of galaxies at a wide range of masses, while
contributing significantly to the metal enrichment of the Universe.
theoretical success in understanding the physics of type Ia events,
measurements of the supernova Ia rate in local and intermediate-redshift
galaxies have illustrated our remarkable ignorance regarding the
the type Ia progenitor population. In this talk, I will present
results from a recent
analysis of the large-scale environments of local type Ia supernovae,
provide an intriguing constraint on the properties of type Ia
Jun 11th 2009 @ 11:30am
Constrained simulations of the local universe
During the last decade our understanding of the evolution of structure
in the universe grew substantially. Due to the non-linear nature of
the gravitational dynamics and the complicated gas-astrophysical
processes numerical simulations on modern supercomputers have been the
driving force behind much of this theoretical progress.
Cosmological simulations must cover a large dynamical and mass range.
A representative volume of the universe should be large, but this
comes at the expense of the resolution. To overcome this problem a
new, and almost orthogonal but yet complementary, approach to
cosmological simulations has been introduced over the last few years.
This consists of using observations of the nearby universe as
constraints imposed on the initial conditions of the simulations. The
resulting constrained simulations successfully reproduce the local
large scale structure, where 'local' means a few tens of megaparsec
around the Milky Way. These simulations are the numerical analog of
the 'Near Field Cosmology', and provide a laboratory for studying the
formation of our Local Group and its environment. I will review our
constrained simulations performed in collaboration of research teams
in Spain, Israel, Germany and USA and compare predictions of the cold
and warm dark matter scenarios with recent observations.
Jun 9th 2009 @ 11:00am
Advanced Architectures for Astrophysical Supercomputing
Jun 4th 2009 @ 11:30am
Magnetic fields and protostellar disks
Magnetic fields are thought to regulate the “accretion phase” of star formation. They do so by transporting away the excess angular momentum of the disk material, enabling it to accrete. The mechanisms responsible for this transport are not well understood, but the most promising are “turbulence viscosity” driven by the magnetorotational instability and “outflows” driven centrifugally from the disk surfaces. Both processes are, in turn, likely to play key roles in the structure, dynamics and evolution of protostellar disks. For example, magnetically driven turbulence is likely to have an effect on the transport and sedimentation of dust particles; in turn critical processes for the formation and migration of planets.
In protostellar disks, however, the magnetic diffusivity may be high enough to prevent the magnetic field to effectively couple to the gas and drive these processes. As a result, in order to study the magnetic activity of these disks under realistic conditions, it is essential to consider carefully the conductivity of the gas and its spatial dependency. Our models of the radial (via the MRI) and vertical (via winds and outflows) angular momentum transport mechanisms in weakly ionized media incorporate the detailed ionization structure of the fluid and all relevant field-matter diffusion mechanisms. Here I examine the viability and properties of these processes in protostellar disks and present our solutions. Our results suggest that, despite the weak ionization, magnetic fields are dynamically important over a broad range of fluid conditions and field strengths in these objects.
May 28th 2009 @ 11:30am
(Univ. of British Columbia)
Searches for New Pulsars
May 15th 2009 @ 11:30am
18 months Ph.D. review
May 14th 2009 @ 11:30am
Galactic Archaeology in our own backyard
Galaxies, like our own Milky Way, have grown over time
through the accretion of smaller galaxies, and the remnants
of ongoing accretions should be apparent within the Local
Group. In this talk, I will present the results of an ongoing
deep imaging survey of the haloes of our nearest large neighbours,
M31 and M33, which has been coupled with stellar kinematics
to reveal a spectacular wealth of streams, lumps and bumps which
clearly illustrate that galaxy evolution is alive and well in
the Local Group.
May 5th 2009 @ 11:30am
LISA and Pulsar timing: upcoming new windows in astrophysics &
In the next decade the detection of gravitational
waves will (hopefully) be a reality, opening a
completely new window on the Universe. The primary actors on
this upcoming stage are expected to be massive black hole binaries.
After a short introduction about hierarchical galaxy
and MBH formation, and GW detection, I will discuss the
possibility of constraining black hole
formation and cosmic evolution scenarios using the planned
laser interferometer space antenna (LISA) and pulsar timing arrays
(PTAs), assessing their capability of providing unique high (and
low)-redshift information difficult to obtain by other means.
Apr 30th 2009 @ 11:30am
The Anglo-Australian Planet Search: Selection Effects, New Planets & Long Winter Nights
I will give a review of the current status of the Anglo-Australian Planet Search (AAPS). The AAPS is one of the oldest Doppler velocity planet searches in the world, having been running over 11 years. Throughout this time we have improved our velocity precision to ~1m/s or better. I will discuss both recent AAPS discoveries and my study of selection effects and observational biases; the latter has made use of the Swinburne supercomputer. I will also look at the future challenges to Doppler velocity programs, not least of which are the stars themselves.
Apr 23rd 2009 @ 2pm
** note unusual time **
Metallicity Gradients at Large Galactocentric Radii Using the NIR
We develop a new technique to extract galaxy halo light
spectra at large galactocentric radii using the DEIMOS multi-object
spectrograph. We use the metallicity sensitive Calcium triplet to obtain
reliable metallicity gradients out to unprecedented radii (2.5r_e) in
large early-type galaxies. The shape and slope of metallicity gradients
with galactocentric radius contain information about the formation and
evolution of galaxies. Results of our pilot study are presented and
compared to theoretical models to constrain the processes involved in
the formation and evolution of individual galaxies.
Apr 22rd 2009 @ 10:30am
** note unusual time **
Cosmos versus Canvas: Tensions between Art and Science in Astronomy Images
Bold colour images from telescopes act as extraordinary ambassadors
for astronomers because they pique the public's curiosity. But are
they snapshots documenting physical reality? Or are we looking at
artistic spacescapes created by digitally manipulating astronomy
images? This lecture provides a tour of how original black and
white data from the Hubble Space Telescope, for example, are
converted into the colour images gracing magazines. Each image is
a battlefield where the attempt by scientists to represent their
discoveries all but drowns out the voice of visual literacy. Yet
sometimes in this battle, between the cultures of science and
visual art, both sides win. This struggle will be presented from the
perspective of a professional astronomer who has coordinated the
Hubble Heritage Project and also trained as an artist. This lecture outlines how artistic techniques - such as colour contrast and composition - can be used by professional astronomers, inspired by the International Year of Astronomy 2009, to produce a more engaging image with greater clarity for the non-expert public.
Mar 26th 2009 @ 11:30am
The Kinematics of Extended Gaseous Halos of Galaxies: Beyond 25 kpc
We lack a thorough understanding, both observationally and
theoretically, of how feedback from star formation, winds and inflows
precisely affect the dynamics of galaxies and their extended
halos. Here, we attempt to disentangle the rather complex coupling
between these processes using both observations and simulations of
extended gaseous galaxy halos. MgII absorption lines detected in the
spectra of background quasars can be used to probe the kinematics and
physical conditions in the halos of foreground galaxies. By comparing
halo gas kinematics to the dynamics of the host galaxies themselves, a
clear picture of the galaxy-halo relationship begins to emerge. We
further compare the high quality absorption data and galaxy spectra
with similarly-analyzed LCDM cosmological simulations. Together, they
suggest a picture in which gaseous halos are chemically enriched by
outflowing shock-heated supernovae winds while low metallicity gas
inflowing along filaments produces an inhomogeneous temperature,
velocity, and metallicity distributions with a non-unity gas covering fraction.
Mar 19th 2009 @ 11:30am
Precision Pulsar Timing, Gravitational Waves, and the ISM
Several ongoing high-precision pulsar timing experiments are now
regularly achieving timing precisions at the several hundred ns level,
and sub-100-ns in the best cases. This has led to renewed worldwide
interest in the idea of a pulsar timing array (PTA), where timing
measurements of a group of MSPs are combined to act as a gravitational
wave (GW) detector, sensitive to nHz-frequency GWs. The expected GW
signal strength is in the 1-10 ns range, so a robust detection requires
roughly an order of magnitude improvement in timing. In this talk I
will describe the ongoing NANOGrav pulsar timing array project, the
prospects for near-future PTA GW detection, and the challenges that we
face in trying to achieve the next order of magnitude improvement. In
particular, I will focus on recent work aimed at characterizing and
removing the effect of the ionized intersterllar medium on pulsar
Mar 12th 2009 @ 11:30am
Understanding Galaxy Formation via Structural Analysis: Observations & Semi-Analytical Models
Many galaxies display distinct, identifiable structural components: commonly (in
massive systems) a central bulge and a surrounding disc, as well as bars,
nuclei, and spiral arms. Moreover, the hierarchical clustering theory of
galaxy formation postulates the existence of two fundamental evolutionary
pathways: the cooling of gas inside rotating dark matter halos to form discs,
and the merging of similar-sized discs to form spheroids and classical bulges.
Hence, understanding the nature of these distinct structural components could
prove crucial to understanding a range of galaxy formation processes.
In this talk I will describe my recent and on-going work on automated structural
decomposition of galaxy images regarding the relationship between galaxy
structural type and position on the color-concentration bimodality, and discuss
the implications of my results for contemporary formation scenarios.
Mar 5th 2009 @ 11:30am
Ashley J. Ruiter
Evolutionary Channels of SNe Ia Progenitors and their Associated Delay Times
Type Ia supernovae are the most important distance indicators used in astrophysics, and play an important role in constraining cosmological quantities. However, despite their use as 'standard candle' distance indicators, their origin remains uncertain. I will discuss the preliminary results from an ongoing study in which we have calculated the delay time distribution - time from star formation to time of SN Ia - for different SN Ia progenitor classes. I will compare the delay times resulting from different formation channels (single white dwarf and double white dwarf formation channels) for varying model parameters (e.g., common envelope removal efficiency). By comparing synthetic delay times with those which have been derived from observations, we aim to constrain the nature of the SN Ia progenitors.
Mar 3rd 2009 @ 11:30am
(Las Campanas Observatory)
Examining quasar accretion discs through micorlensing
I present a novel method of constraining AGN emission region size and emission mechanism, using recent optical--NIR imaging from the Magellan telescopes of four ``anomalous'' lensed quasars.
Anomalous lensed quasars have an image pair in which one of the images is unusually ("anomalously") dim. We rule out millilensing and partial obscuration as causes for the anomalous flux ratio in each of our quasars, leaving microlensing as the only plausible alternative. We generate magnification maps for each image using a range of smooth-to-clumpy matter fractions. We then randomly select source positions on the map and calculate the magnifications of a set of Gaussian sources of varying width. We are thus able to constrain statistically, both the proportion of smooth-to-clumpy lensing material, and the size of the emitting region of the lensed source.
Using this technique we have probed down to unprecedented scale lengths in the central engine (< 7 light days in r' band) and have begun to explore the change with wavelength. We find clear evidence of a decrease in source size with wavelength, and can place meaningful constraints on possible emission mechanisms.
Feb 26th 2009 @ 11:30am
(University of Queensland)
The origin of ultra-compact dwarf galaxies
When we originally discovered ultra-compact dwarf (UCD) galaxies in the Fornax and Virgo galaxy clusters their properties were clearly intermediate between the most luminous globular clusters and the smallest dwarf galaxies. Our favoured theory was that they were the stripped nuclei of nucleated dwarf galaxies. Five years on, the situation is not so clear, as I will discuss in this talk.
The structural properites of UCDs in the "fundamental plane" show them to be clearly distinct from globular clusters, but their stellar populations show they mostly resemble globular clusters with old populations. Our dynamical simulations are consistent with some kind of disruptive formation process, but this would have to be from galaxies with unusually old nuclei. There are no solid theoretical predictions of how UCDs form, so we are now working with members of the Virgo Consortium to predict how UCDs could form using cosmological simulations.
Feb 20th 2009 @ 11:30am
Redshifted 21cm Radiation and Reionization
Over the last decade observational cosmology has matured to the point where
quantities such as the mass, composition and age of the Universe are now
measured with a precision of a few percent. In contrast, the formation of
the first galaxies remains very poorly understood. For example, we do not
know at what time the first galaxies formed, what they looked like or how
massive they were. The origins of this ignorance lie in observational
difficulties associated with observing high redshift galaxies. However one
fact is known. Three hundred thousand years after the Big-Bang the Universe
was filled with atomic hydrogen, which was then reionized by starlight from
the first galaxies over the next billion years. A new era for study of the
first galaxies will therefore open with the next generation of low-frequency
radio-telescopes, which will enable the reionization of the Universe to be
studied directly. I will discuss some of the associated science, with some
emphasis on the role that theory has played in motivating the experiments
and the design of new telescopes like the MWA.
Feb 17th 2009 @ 9:00am
David Palamara (U. Monash)/ Sophie Underwood (U. Adelaide)
(Gemini Observatory, Chile)
Australian Gemini Undergraduate Summer Student (AGUSS) Seminar
Each year the Australian Gemini Office coordinates the AGUSS scheme, sponsored by Astronomy Australia Ltd, to allow Australian undergraduate students to spend 10 weeks working at the Gemini South Observatory in Chile. At the conclusion of their program, the students present their results by video-conference to multiple sites in Australia. Everyone is welcome and encouraged to come and hear what this year's AGUSS students have been up to. David Palamara from Monash University will talk about infrared studies of globular cluster candidates in galaxy merger remnants, while Sophie Underwood from the University of Adelaide will talk about peculiar velocities of cluster galaxies.
(We'd be joining with video conferencing in the CAS meeting room. Live video streaming will be available from https://184.108.40.206/showstream.ssi to machines within Swinburne only)
Feb 13th 2009 @ 11:30am
(Institut de Physique Nucléaire de Lyon)
Bulk Motions of Filaments in the Local Universe
Galaxies acquire motions that deviate from the universal expansion through
gravitational interactions on a wide range of scales. The radial component
of these deviant motions can be mapped with accurate measurements of
distances. One of a variety of ways to measure distances makes use of the
correlation between the luminosities of galaxies and their rotation rates.
With appropriate photometric and spectroscopic information, the method can
be applied to a majority of spiral galaxies. Samples of many thousands of
galaxies can be acquired, giving the dense spatial coverage required to
study the streams and eddies in the Cosmic Flow.
Feb 6th 2009 @11.30am
(Liverpool John Moores)
The evolution of the u-band galaxy luminosity function: Can a universal stellar IMF survive?
Feb 5th 2009 @ 3pm
Andrew Hopkins (Head of AAT Science)
Progress and Opportunities at the AAO
Recent developments at the AAO on both scientific and instrumentation
fronts will be presented. These include research results from AAO staff,
an overview of the ongoing AAT Large Programs (Anglo-Australian Planet
WiggleZ, GAMA), progress on the WFMOS concept study, the HERMES instrument,
and a striking demonstration of the OH suppression fibre technology.
Opportunities for students at the AAO will also be highlighted, including
PhD top-up scholarships, as well as the currently open Magellan Fellow
Jan 29th 2009 @ 11:30am
`Cold Fronts' as Merger Indicators in Clusters of Galaxies
Cluster mergers are at the pinnacle of the large scale structure
hierarchy, and involve the largest, most massive virialised objects
present epoch. The effects of this violent merging environment on the
constituents (galaxies, intracluster medium and dark matter) are not
understood. Studies in this area are hindered by difficulties in
whether a cluster is undergoing, or has recently undergone, a merger
distinguishing major mergers from minor. We have developed a new and
approach to solving these problems, whereby X-ray `Cold Fronts'
Chandra images are used as possible signposts of recent merger
order to gain confidence in the use of cold fronts as
have selected a sample of `Cold Front' clusters from the Chandra
are conducting extensive optical spectroscopy of these systems to
otherwise) they have undergone a recent major merger event, and
the link between cluster dynamical evolution and the cluster galaxy
In this talk I will present the Cold Front sample, its selection
describe the studies we have undertaken with the AAT/AAOmega and
spectrographs of two important test cases: Abell 1201 and Abell 3667.
two clusters I will present methods and results of the sub-structure
analysis and show a causal link between the observed cold fronts and