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.

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.

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.

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.

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.

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.

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.

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.

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.

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 Mission.

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 of research.

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.

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.

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.

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.

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.

(This is a joint AAO/ATNF Astrophysics Colloquium and we'd be joining via video conference from the CAS meeting room AR101b).

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.

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 Field South.

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.

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.

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.

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).

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.

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.

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.

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.

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.

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.

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.

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.

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 radio source.

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.

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