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Colloquia Series

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

Swinburne Virtual Reality Theatre
AR Building, Room 104
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2007 Colloquia

Dec 13 @ 11:30
Marijke Haverkorn (Berkeley)
Title: The turbulent life and times of the Galactic interstellar medium
Over the past decades, the paradigm describing the Galactic Interstellar Medium (ISM) has shifted from individual `clouds' in thermal equilibrium to a highly non-equilibrium dynamically evolving medium where gaseous components, magnetic fields, and cosmic rays are in continuous interaction. Studies of this turbulent ISM help us understand physical processes such as how and where molecular clouds form stars, the energy sources that stir up the gas and how much turbulence contributes to the heating of the ISM. In addition, turbulence heavily affects the structure and strength of the Galactic magnetic field (and vice versa), and it plays a crucial role in the propagation of cosmic rays. I will discuss observational studies of Galactic turbulence, focusing on the diffuse ionized gas, and what we have learnt from those. This includes recent estimates of typical scales of fluctuations in the interstellar gas through depolarization studies of Galactic and extragalactic synchrotron emission, and estimates of the strength and structure of the magnetic field. Furthermore, I will briefly introduce several recent, ongoing and planned radio surveys of the polarized ISM and some preliminary or expected results.
Nov 29 @ 11:00 - 16:00
Melbourne Astro Day
Nov 27 @ 11:30
Joris Verbiest (Swin)
Title: Pulsar Timing and Power Spectra (or: How to uncover the Universe and be sure of it.)
The technique of pulsar timing has long been used to uncover scientific phenomena that are difficult, or impossible, to study by any other means. In particular timing of pulsars with millisecond periods (MSPs) has provided a wide variety of results, including stellar masses, independent distances, the first detection of extra-solar planets and the first indirect detection of gravitational waves (GWs). Presently, astronomers all over the world are using MSP timing in an attempt to make the first direct detection of a GW background, which would be expected based on models of hierarchical galaxy formation and inflation in the early Universe, amongst others. In this talk I will present some of the most precise long-term timing data sets presently available and use these to illustrate two recently developed lines of research based on the power spectrum of the pulse arrival time residuals (i.e. actual pulse arrival times subtracted from a model). The first of these is a simple yet robust technique to place limits on the strength of stochastic GW backgrounds. The other uses power spectra to enable realistic Monte-Carlo simulations of pulsar timing data. This allows, for the first time, a rigorous analysis of measurement uncertaincy in pulsar timing, an important but long-ignored aspect in this field.
Nov 22 @ 11:30
Bryan Gaensler (University of Sydney)
Title: TBD
Nov 20 @ 11:30
David Wiltshire (University of Canterbury in Christchurch)
Title: Gravitational energy as dark energy - towards concordance cosmology without Lambda
A decade of observations suggest 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.
Nov 15 @ 11:30
Chris Power (Swinburne)
Title: The Certainty of Doubt -- What can we know about the Dark Matter?
One of the cornerstones of modern theories of cosmological structure formation -- and therefore galaxy formation -- is that the matter content of the Universe is dominated by some form of non-baryonic Cold Dark Matter. This CDM model makes two key predictions -- that dark matter haloes are cuspy, and that the halo number density increases sharply with decreasing mass. Cuspy haloes are a generic prediction of any hierarchical model, whereas the increasing abundance of small scale structure with decreasing mass is characteristic of the CDM model. But how cold is cold? In this talk I will discuss what we (think we) know about dark matter halo mass profiles and their physical origin. I will review some recent work on halo equilibria in the CDM model and halo structure in scale-free cosmologies. I will then consider what we (think we) know about the low-mass end of the halo mass function, and discuss the difficulties inherent in comparing theory and observation. Finally, I will argue that measurements made in our Galaxy's dark matter halo -- by gamma-ray telescopes such as GLAST, by drift experiments such as CDMS and DAMA, and next generation particle colliders such as the ILC -- should provide us with important limits on the dark matter particle.
Nov 13 @ 11:30
Dave Lommen (Leiden)
Title: Multi-wavelength observations of grain growth in protoplanetary disks
Low- and intermediate-mass stars form as interstellar clouds collapse under their own gravity. Due to the angular momentum present in the cloud, all the matter cannot fall directly onto the new star, and a disk forms around it. It is in these protoplanetary disks that planets are formed. The dust grains in the interstellar clouds, and hence in the initial disks, have typical sizes smaller then microns. Over the course of a few million years, they must coagulate and grow to form planets, thousands of kilometres in size. By using observations, ranging from infrared to millimetre and centimetre wavelengths, we study how the grains grow in these early and important steps of planet formation.
Nov 8 @ 11:30
Michael Brown (Monash)
Title: The Past 8 Billion Years of Red Galaxy Growth
The growth of galaxies is one of the key unresolved issues in modern astrophysics. In a universe where the bulk of the mass is in the form of collisionless cold dark matter, the most massive dark matter halos (gravitationally bound structures of dark matter) grow rapidly via mergers at z<1. In contrast, there is strong evidence that many massive galaxies formed prior to z=1. Using the NOAO Deep Wide-Field and Spitzer IRAC Shallow surveys, we have measured the evolving space density and clustering of z<1 red galaxies with unprecedented precision. We have then used our measurements to determine the dark matter masses of galaxy populations. Remarkably, how galaxies occupy dark matter halos appears to have changed very little over the past 8 billion years. In the most massive halos, much of the stellar mass resides within satellite galaxies, indicating that halo mergers do not always efficiently funnel stellar mass into central galaxies. The stellar mass of central galaxies is proportional to halo mass to the power of a third, and we thus conclude that massive galaxies do not grow as rapidly as their host dark matter halos.
Nov 1 @ 11:30
Brian Schmidt (ANU)
Title: The SkyMapper Telescope and Southern Sky Survey
SkyMapper is among the first of a new breed of surveying telescopes which are able to scan the nighttime skies more quickly and deeper than ever before. SkyMapper is a 1.3m telescope featuring a 5.7 square degree field of view Cassegrain imager with a 268 Megapixel focal plane, and will commence regular operations in 2008. I will overview the telescope hardware and software features, updating the audience on progress towards regular operations. For its first 5 years of operations, 75% of all observing time will be dedicated to undertaking the Southern Sky Survey, a 2 pi steradian six colour, multi-epoch photometric survey of the southern sky to g ~23 mag. I will detail this survey and its data products, sketching the main scientific objectives, and hopefully engage with the audience about any particular desires that they have from the survey.
Oct 25 @ 11:30
Kevin Pimbblet (University of Queensland)
Title: A Voyage beyond the Cluster Core
We can no longer consider clusters of galaxies to be isolated objects in space. They are connected in a non-trivial manner to the other, large scale structure of the Universe by sheets, walls and filaments of galaxies. These filaments of galaxies provide an excellent tool to study structure formation and galaxy evolution in a novel manner. In this talk, I will outline my interest in filaments of galaxies over the past 5 years; discuss various detection strategies; and talk about our recent work that suggests filaments of galaxies are responsible for a rapid burst of star formation at around the critical density for galaxy evolution, before their star formation rate plummets as they accrete on to clusters -- an effect that is not seen by simply using local galaxy density to probe the origins of galaxy evolution.
Oct 24 @ 16:00
Kenji Bekki (University of New South Wales)
Title: Globular cluster systems and galaxy formation
We discuss the origin of physical properties of globular cluster systems (GCSs) in galaxies in terms of galaxy formation and evolution processes. Based on numerical simulations of dynamical evolution of GCSs in galaxies, we particularly discuss (1) the origin of radial density profiles of GCSs in early-type galaxies, (2) formation of He-rich GCs in the Galaxy, (3) the origin of GCSs in the Large Magellanic Cloud, (4) formation of intragroup and intracluster GCs, and (5) evolution of giant molecular clouds into GCs in low-mass halos at very high redshifts.
Oct 11 @ 11:30
Adam Deller (Swin)
Title: Pulsar astrometry with VLBI
While multiple methods exist to estimate the distance and transverse velocity of individual pulsars, VLBI astrometry potentially suffers the least from systematic errors (and hence is the most accurate) since: 1) Measurements are tied to the (quasi-)inertial celestial reference frame 2) It does not rely on timing and as such is unaffected by secular or periodic evolution in pulse properties, and does not require high timing accuracy 3) It does not contain model dependencies on the line of sight ISM, as is required for estimates of distance via Disperion Measure (DM) and transverse velocity via scintillation However, pulsars are challenging astrometric targets for VLBI, being relatively faint and possessing steep spectrums. In this talk, I will describe my current VLBI astrometry program with the Australian Long Baseline Array (LBA) and highlight the difficulties faced by these observations, as well as the potential science payoffs.
Oct 10 @ 15:00
Greg Poole (Swin)
Title: The Effects of Mergers on Relaxed X-ray Clusters
A remarkable renaissance in the study of galaxy clusters is underway. However, despite this revolution, one of the oldest observations of the field remains poorly understood: the existence of systems with high and peaky central X-ray surface brightnesses (traditionally known as "cooling flow" clusters) and those with low and flat central X-ray surface brightnesses (traditionally known as "non-cooling flow" clusters). It has been a tacit belief for some time that cooling flow systems represent a population of relatively undisturbed systems while non-cooling flow systems are those which have suffered recent major mergers, but the issue has received remarkably little detailed consideration. I have set-out to test this hypothesis using simple idealized hydrodynamic numerical simulations of galaxy cluster mergers. In this talk I will use these simulations to show that the compact cores responsible for the properties of cooling flows are remarkably stable to the effects of mergers. In the process I will also illustrate the complex phenomena that manifest during cluster mergers (eg. the "cold fronts" and surface brightness "edges" observed in many Chandra and XMM observations), discuss the optimal criteria for measuring the dynamical state of clusters and illustrate the effects of mergers on cluster scaling relations (particularly relevant to the use of clusters as precise cosmological probes).
September 27 @ 11:30
Paul Kiel (Swin)
Title: Populating the Galaxy with Pulsars
The majority of pulsar population synthesis studies performed to date have focused on isolated pulsar evolution. Those that have incorporated pulsar evolution within binary systems have tended to either treat binary evolution poorly of evolve the pulsar population in an ad-hoc manner. Here I present the first model of the Galactic field pulsar population that includes a comprehensive treatment of both binary and pulsar evolution. Synthetic observational surveys mimicking a variety of radio telescopes are then performed on this population. As such, a complete and direct comparison of model data with observations of the pulsar population within the Galactic disk is now possible. The tool used for completing this work is a code comprised of three components: stellar/binary evolution, Galactic kinematics and survey selection effects. Here I give a brief overview of the codes, including the methods and assumptions involved with each component. Some preliminary results are also presented as well as plans for future applications of the code.
September 21 @ 11:30
Annie Hughes (Swin)
Title: Cold gas and dust in the Large Magellanic Cloud
At an assumed distance of only 50 kpc, the Large Magellanic Cloud presents a unique opportunity to study at an entire galaxy at high angular resolution. A gas-rich, dwarf irregular with clear signs of active star formation, the LMC is an excellent laboratory to investigate the relationship between different phases of the interstellar medium (ISM), the interaction of the ISM with individual objects, and the influence of galactic-scale processes on the properties of interstellar material. In this talk, I will present a short review of two projects about the ISM in the LMC that I have been working on for my thesis. First, I will discuss what we have learnt about the origin of the global radio-FIR correlation by studying the relationship between the radio continuum and IR emission locally within the LMC. In the second half of my talk, I present a few results from our Mopra survey of 12CO(J=1-0) emission from molecular clouds in the LMC.
September 13th @ 11:30
Quentin Parker (Macquarie University)
Title: The Macqaurie/AAO/Strasbourg H-alpha PN project: MASH
Planetary nebulae (PNe) are powerful astronomical tools. They probe nucleosynthesis processes, abundance gradients and chemical enrichment of the ISM, and act as powerful tracers of our Galaxy's star-forming history. Their strong emission lines make them detectable to large distances and also permit determination of accurate velocities so they are also excellent kinematical probes. Their spectra enable determinations such as excitation class, measurement of electron temperature, density and abundances of the nebula gas. I report on discoveries and preliminary results from our unprecedented surveys of PNe in our Galaxy and Large Magellanic Cloud under the umbrella of the Macquarie/AAO/Strasbourg H-alpha Planetary Nebula project: MASH. In particular I report on a surface-brightness radius relation developed by team member Frew which offers a powerful new mechanism for distance determinations.
September 4th @ 11:30
Filipe Abdalla (UCL)
I will first give a broad overview of gravitational lensing and current results and the theoretical issues arising. I will then talk about the photometric redshift issues in gravitational lensing concentrating especially on the requirements needed so that future gravitational lensing surveys are not limited by the systematic effects that arise from intrinsic alignments.
August 30th @ 11:00
Alan Alves Brito (Sao Paulo)
Title: NGC 6553: Elemental Abundance Ratios as Fossil Imprints of the Galactic Bulge
Detailed chemical abundance patterns can provide us with valuable information on how the Galaxy formed and has evolved. I will present a detailed abundance analysis of four giants in the metal-rich bulge globular cluster NGC 6553, based on optical high-resolution echelle spectra obtained with UVES at the ESO VLT-UT2 Kueyen telescope. The present spectra are the highest resolution data so far for stars in this cluster. Our results support a rapid chemical evolution history dominated by Type II supernovae in the Galactic bulge.
August 27th @ 11:00
Ilana Feain (ATNF)
Title: Why do high-z radio galaxies have steep spectra?
The correlation between the redshift of a radio galaxy and the steepness of its observed radio spectral index has proven to be the most efficient way to find the most massive galaxies at high redshift. I'll talk a bit about our efforts to find radio galaxies by exploiting this correlation. And what of the origin of the correlation itself? Since massive, steep spectrum radio galaxies in the local universe reside in the densest galaxy clusters, a natural interpretation for the correlation is that radio galaxies at high redshift are located in environments with densities typical of nearby rich clusters.
August 16th @ 10:30
Joe Silk (Oxford)
Title: Galaxy Formation
August 9th @ 11:30
Andrew Bunker (Exeter)
Redshift 6, one billion years after the Big Bang, marks the end of the reionization epoch. A crucial question is whether the UV flux from young starbursts at this redshift is sufficient to achieve this reionzation. We have used the Lyman break technique to identify candidate star-forming galaxies at this redshift in deep HST/ACS images. Using the Hubble Ultra Deep Field, we identified i-band drop-outs as faint as z(AB)=28.5mag, corresponding to unobscured star-formation rates of ~1Msun/yr at z~6. Spectroscopic confirmation of this population is crucial, to guard against low-redshift interlopers (Extremely Red Objects at z~1-2 and low-mass Galactic stars) and to study the Lyman-alpha emission line properties of z~6 galaxies. We have undertaken the deepest spectroscopy yet to achieve this.
August 6th @ 11:00
Chris Tinney (UNSW)
Title: 2006/2007 - An End-of-Financial year Report on Exoplanets
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 and very successful search for Doppler Wobble exoplanets, the Anglo-Australian Planet Search has also completed it's first massive chunk of observing in its "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.
August 2nd @ 11:30
Craig Harrison (MSO)
Title: The Stellar Populations In Early-Type Galaxies
Through analyses of absorption-line indices, and the stellar population parameters age, metallicity, and alpha-element abundance ratio estimated from these indices, we investigate in detail the stellar populations of early-type galaxies in low-redshift clusters, compare the stellar populations in the cores and outskirts of clusters, and track the evolution of early-type galaxies over the last 30% of the Hubble time. These analyses reveal that early-type galaxies in clusters and their outskirts form a relatively homogeneous class of objects that follow trends of increasing metallicity and alpha-element abundance ratio with increasing mass. The distribution of ages is consistent with a down-sizing scenario, with age indirectly correlated with mass through star-formation timescale (i.e. the alpha-element abundance ratio-sigma relation). The intrinsic scatters in their metallicity and alpha-element abundance ratio distributions are remarkably small, and can be accounted for by the distribution of galaxies along the trends with velocity dispersion together with the intrinsic scatter about these trends, which we suggest is a down-sizing parameter (namely the amount of late star formation as a function of velocity dispersion). The low-redshift cluster galaxies are consistent with being passively evolved versions of the galaxies in the intermediate-redshift cluster A0370. The overall picture of the formation of the stellar populations in early-type galaxies that emerges from this work is one of rapid early formation producing a homogeneous class of objects whose properties are largely (but not solely) determined by their mass, and which are subsequently partially modified by wet mergers that are increasingly important for lower-mass galaxies and those in clusters with extended assembly histories.
July 26th @ 11:30
Panayiotis Tzanavaris (Athens)
Title: The galaxy luminosity function and its evolution with Chandra
The X-ray regime offers unique probes into processes in normal, non-AGN dominated, galaxies. I will present the latest results on the local X-ray luminosity function of normal galaxies. Galaxies are selected from four major surveys, providing extended coverage of the luminosity-redshift plane. Our results suggest evolution of the total sample luminosity function with redshift, which is driven by evolution of late-type systems.
July 19th @ 11:30
Karrie Gilbert (Santa Cruz)
Title: Exploring Andromeda's Stellar Halo
In the current paradigm of hierarchical galaxy formation, massive galaxies are built up through a series of major and minor merger events. A consequence of hierarchical galaxy formation is that galactic stellar halos should be at least partially composed of tidal debris from past accretion events. Recent surveys of Andromeda's stellar halo are making great strides towards increasing observational constraints on theories of stellar halo formation. I will discuss recent results on the profile, extent, and metallicity of Andromeda's stellar halo, as well as the amount and extent of tidal debris. I will also present the discovery of the Southeast Shelf, which is most likely the forward continuation of Andromeda's Giant Southern Stream, and which sheds light on the intermediate-age population found in Andromeda's spheroid by deep HST/ACS imaging (Brown et al. 2003).
July 17th @ 11:30
Erik Hoversten (JHU)
Title: Evidence for a Non-Universal Stellar Initial Mass Function from SDSS Galaxies
The stellar initial mass function (IMF) is widely held to be universal- the same everywhere in space regardless of environmental conditions. This is due to the fact that a wide range of IMF measurements agree with each other within the uncertainties. Analysis of the H alpha equivalent widths of 130,602 star forming galaxies in the Sloan Digital Sky Survey shows that luminous galaxies are well fit by a universal, Salpeter IMF. However galaxies on the faint end do not agree with a singly universal IMF and form fewer massive stars than a Salpeter IMF. The implications of these results for theories of star formation and the modeling of galaxies are discussed.
July 5 @ 11:30
Daniel Eisenstein (Arizona)
Title: Dark Energy and Cosmic Sound
I present galaxy clustering results from the Sloan Digital Sky Survey that reveal the signature of acoustic oscillations of the photon-baryon fluid in the first million years of the Universe. The scale of this feature can be computed and hence the detection in the galaxy clustering serves as a standard ruler, giving a geometric distance to a redshift of 0.35. I will discuss the implications of this measurement for the composition of the universe, including dark energy and spatial curvature. I will close with a discussion of the prospects for future redshift surveys to use the acoustic peak to map the expansion history of the universe.
June 28 @ 11:30
Kimitake Hayasaki (YITP Japan)
Title: New Method of the Supermassive Binary Black Holes Explorer in the Universe
We study the accretion flows onto the supermassive binary black holes from the circumbinary disk with the equal mass binary on the subpc scale (the semi-major axis: a=0.1pc), by performing Smoothed Particle Hydrodynamics (SPH) simulations. We find that the material can be supplied from circumbinary disk, which leads to the formation of accretion disks around each of black holes. The mass accretion rates significantly modulate with the binary orbital motion in the case of an eccentric binary after the system reaches the quasi- steady state. Thus, we expect that the spectral energy distributions of accretion disks have also an orbital phase dependence. These could provide the observable diagnosis of the existence of the supermassive binary black holes on the subpc scale in merged galactic nuclei.
June 14 @ 11:30
Gary Da Costa (ANU)
Title: Stellar Populations of dE galaxies in nearby Groups
June 12 @ 11:30
Arna Karick (Lawrence Livermore National Laboratory)
Title: The Stellar Populations of Ultra-compact Stellar Systems.
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.
June 7 @ 11:30
Jeremy Bailin (Swinburne)
Title: Satellite Galaxies: Who, What, Where, How and Why?
I will survey a number of recent exciting results concerning the small satellite galaxies that surround larger, more familiar galaxies. I will introduce some nearby satellite galaxies (who are they?), and focus on the questions of what they are made of, where they are located, how they interact with their parent galaxies, and why they are so important to our understanding of galaxy formation and evolution.
May 29 @ 16:00
Elaine Sadler (University of Sydney)
Title: Cosmic evolution of massive galaxies and radio-loud AGN
In recent years, it has become clear that the evolution of galaxies and their central supermassive black holes are closely linked. Models in which heating by a radio-loud AGN prevents late-time star formation in massive galaxies are also becoming increasingly popular with theorists. The combination of large-area radio continuum and optical redshift surveys provides a powerful tool for studying the co-evolution of massive galaxies and their active nuclei, and I will present some recent results based on radio-detected galaxies in the 6dFGS (z<0.1) and 2SLAQ LRG (0.4
May 11 @ 16:00
Meghan Gray (Nottingham)
Title: STAGES: Galaxy evolution across a supercluster
I will introduce STAGES, a 0.5x0.5 degree Hubble Space Telescope survey of the A901/902 supercluster. We combine extensive multiwavelength data from X-ray to radio to compile a comprehensive view of the complex supercluster environment and the galaxy properties embedded within. Here we present results from space-based gravitational lensing mass reconstructions across 5x5 Mpc, and examine environmental trends of galaxy properties including morphology, age, star-formation and AGN activity. Among our results, we find that the intermediate density regimes marking the infall regions are the preferred sites for a variety of galaxy activity, including active nuclei and dusty star formation.
April 27 @ 11:00
Alyson Ford (Swinburne)
Title: HI Clouds in the Lower Halo of the Galaxy
April 19 @ 11:30
Andrea Lommen (Franklin and Marshall College / ATNF)
Title: A Persnickety Pulsar Experiment
We know shockingly little about the way(s) in which a pulsar actually emits radiation. I will tell you everything we know about the emission mechanism in about 10 minutes. Then I'll tell you about a persnickety time-keeping experiment that we did with simultaneous X-ray (using RXTE) and radio observations (using the Mount Pleasant Radio Observatory in Tasmania) on the Vela Pulsar that gives us a few more hints about the mechanism. In particular, our results establish a relationship between radio and high-energy emission that was previously unknown.
April 11 @ 11:30
Frazer Pearce (Nottingham)
Title: The Millennium Gas Simulations
Re-running the Millennium volume with increasing amounts of physics. Billion particle hydrodynamic simulations.
March 22 @ 11:30
Jason Kalirai (UCO/Lick Observatory)
Title: The Stellar Populations of the Andromeda Spiral Galaxy
Simulations of hierarchical galaxy formation suggest that large galaxies such as the Milky Way and Andromeda (M31) should contain extended stellar halos that are chemically distinct (more metal poor) from the inner spheroid. Yet, no such population has been discovered in our nearest neighbor, M31. We report on the first results from a photometric and spectroscopic survey of red giant branch (RGB) stars over a large expanse in M31. Using a new technique based on photometric and spectroscopic diagnostics, we are able to isolate bonafide M31 RGB stars out to a distance five times further than previous studies (165 kpc). In addition to the kinematically cold disk and metal-rich inner spheroid, we find clear evidence for an extended, power law halo component in M31. The spectroscopic and photometric metallicity of this new population is measured independently and found to be metal-poor, [Fe/H] = -1.5. We also present the discovery of a new dwarf spheroidal galaxy in M31 and evidence for spatial and kinematical substructure in the halo. The discovery of this stellar halo puts to rest much of the disparity that has existed between the Milky Way and M31 halos.
March 16 @ 12:00
Richard Ellis (Caltech)
Title: The Thirty Meter Telescope
Progress of the Thirty Meter Telescope project.
March 15 @ 11:30
Attila Meszaros (Charles Univ. Prague)
Title: Cramer theorem and the gamma-ray bursts
At the beginning of the seminar a brief survey of the topic of the gamma-ray bursts will be given. Then a paper of author will be presented (A&A, 401, 129, 2003). This paper uses a mathematical theorem (Cramer theorem) in order to prove that the short and long gamma-ray bursts are physically different phenomena. This procedure in astronomy is so surprising and curious that this method can be interesting for the non-specialists, too.
March 13 @ 16:00
Richard Ellis (Caltech)
Title: Characterizing the Sources Responsible for Cosmic Reionization
I will review recent progress in charting the early star formation history of galaxies and present the latest results from Keck and HST surveys for z~8-10 sources.
March 13 @ 11:30
Chris Brook (Washington)
Title: Self-Consistent Simulations of Disk Galaxy Components
We will review recent progress made in disk galaxy simulations, and use the latest simulations as aids in interpreting aspects of disk galaxy formation. We will touch on issues ranging from the first (Pop III) stars (where are they now?), to disk growth (inside out?). Emphasis will be on the old components, the stellar halos and thick disks, and what they can tell us about galaxy formation.
March 8 @ 11:30
Larry Widrow (Queens)
Title: Galaxies by Design
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 providing 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 three applications: the structure and dynamics of the Milky Way, a surprising connection between dark halos and bar formation, and the latest results from microlensing explorations of the Andromeda galaxy.
March 6 @ 12:00
Pavel Kroupa (Bonn)
Title: The stellar initial mass function
The stellar initial mass function (IMF) is one of the most important distribution functions in astrophysics. It constitutes the relative number of stars of different mass and is therefore fundamental for understanding how galaxies evolve on scales of many kpc. The IMF is a result of star-formation occurring on pc-scales and, if measured, constrains star-formation theory. The problem though is that stellar masses cannot be measured directly, so the IMF has to be deduced from the distribution of stellar luminosities.
The IMF has indeed been constrained to a reasonable degree of accuracy for Galactic-field populations and for on-going star-forming regions. I will discuss the methods of extracting the actual stellar IMF from observations, and will emphasise stellar-dynamical biases. The data suggest the IMF to be surprisingly invariant. This is in disagreement with expectations from star-formation theory, and this issue remains unsolved but interesting. Furthermore, assuming the IMF to be invariant implies that galactic-field populations have steeper field IMFs for massive stars which vary with the star-formation history of the galaxy. This has important implications for understanding galactic evolution in a cosmological context.
March 2 @ 15:00
Visiting Professor Open Talk
Pavel Kroupa (Bonn)
Title: From Exoplanets to Dark Matter: Modern Challenges in Astrophysics
Newton derived his equation of motion from observations gained from the immediate vicinity of the observer. This equation constitutes an excellent description of the motions of the planets. These show certain regularities of the shapes of their orbits about the Sun. The planets about other stars, the ExoPlanets, do not show these regularities. One part of this talk will discuss the possible meaning of this in terms of the nature and origin of planets, and the possible implications for harboring life. Applied to the motion of stars about galaxies, Newton's equation shows that the stars move differently to the way they should be moving. This extrapolation by many orders of magnitude of Newton's equation thus may indicate Newton to be wrong therewith uncovering "new physics". The other part of this talk will address this problem and possible solutions, the most popular of which is the postulate that the universe is filled with dark matter. But is this the only solution possible?
February 22 @ 11:30
Robert Izzard (Utrecht)
Title: Solving the century-old R star mystery
I review the history of the R-type carbon stars, from their discovery the late 19th century to modern spectroscopic analyses. Despite being quite common, the origin of these stars remains a mystery. With the aid of a stellar population and nucleosynthesis model I discuss what they can, and cannot, be.
Jan 18 @ 11:30
Peter Thomasson (Jodrell Bank)
Title: e-Merlin Developments
Jan 11 @ 11:30
Chris Lidman (ESO)
Title: Decelerating and Dust Free: Observations of Type Ia supernovae in the ellipticals of high redshift galaxy clusters.
Observations of Type Ia supernovae (SNe Ia) have played, and continue to play, an important role in constraining the properties of dark energy, a mysterious form of energy that currently dominates the energy density of the universe and drives the acceleration at the current epoch. The current generation of large SNe Ia surveys (SNLS, ESSENCE and the SDSS supernova survey), which are observing hundreds of SNe Ia over the course of several years, have shown than Einstein's cosmological constant is still an acceptable description of dark energy. However, there are viable alternatives to the cosmological constant. Separating these possibilities using SNe Ia in even larger surveys will be slow as the constraints from SNe Ia observations are starting to be limited by systematic errors. One of the biggest sources of systematic and statistical error comes from the correction for extinction by dust in the host galaxy. Elliptical galaxies are largely free of dust, thus raising the possibility that SNe Ia in elliptical galaxies are better standard candles. In this talk, I will describe a project that is using the ACS camera on HST and large ground based telescopes to discover and follow SNe Ia that are hosted by the elliptical galaxies in distant rich clusters. We have now completed the observational part of the project and have started to analyse the data. From a preliminary analysis of the data, we have found that the dispersion of these SNe about the Hubble line is quite tight.