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| Date | Speaker | Topic |
|---|
| September 12 |
Will Sutherland
(QMUL) |
Baryon Acoustic Ocsillations |
| The baryon acoustic oscillation (BAO) feature in large-scale galaxy clustering is probably the best standard ruler in the moderate-redshift universe. I will provide a review of current observations of BAOs and future prospects, and then show how an "ultimate" full-sky BAO survey at z ~ 0.25 can provide major benefits: both a model-free check of cosmic acceleration, and a potential test of the cosmic radiation density. |
| September 19 |
Filipe Abdalla
(UCL) |
Looking through our Galaxy, the epoch of reionisation and foreground removal |
| We live in exciting times as we have for the first time radio instruments which will allow us to collect enough data to be able to see the epoch of reionisation directly via the 21cm line emission. However this measurement will be plagues with technical difficulties one of which is the removal of the signal coming from our own galaxy as well as extragalactic foregrounds. I will review briefly the physics happening in the formation of the signal and also present results on how to remove this signal with techniques currently proven in the area of CMB data analysis, including FastICA and GMCA. |
| September 26 |
Martin Stringer
(Observatoire de Paris) |
Going Ballistic! The fundamental physics and observational signatures of supernova winds |
| Any viable theory of the formation and evolution of galaxies should be able
to account for the mass of baryons contained, or rather not contained, in
the massive collapsed regions that host galaxies. Supernova winds are now an
accepted part of the explanation for this deficit, yet citations to this
effect often list from a vast melee of modelling strategies and numerical
simulations, rather than elegant analytic treatments of the process from the
1970s. By re-examining these classic works, and re-applying them with the
hindsight of modern cosmology, I will show that these theories seem to have
successfully predicted the connection between between baryon content and
galaxy circular velocity that we now find in recent observational surveys.
So do our sophisticated simulations simply corroborate the traditional
assumptions that were applied? Or are we all arriving at the right answer,
but for the wrong reasons..? |
| October 3 |
Rene Breton
(Southampton) |
Measuring Pulsar Masses in Black Widow and Redback Systems |
| Typical neutron star densities are beyond the reach of Earth laboratory experiments and the study of their equation of state can provide important knowledge about the behaviour of ultra-dense matter. While the neutron star equation of state remains elusive due to observational challenges (e.g. namely the lack of reliable simultaneous mass and radius measurements), the most massive neutron stars constrain it to increasingly stiff models. The most promising candidates to search for massive neutron stars are the binary millisecond pulsars, which are old, once-slowly rotating pulsars that have been spun-up by accreting mass from a close companion star. Empirically, the so-called black-widow systems seem particularly promising: for the prototype system, PSR B1957+20, we recently inferred a mass of 2.4 solar masses. If confirmed by further study, this would make it the heaviest know neutron star. In this talk, I will describe how the light curve and spectrum of the strongly irradiated companion was used to determine the black-widow pulsar mass. I will also discuss perspectives of several new mass measurements in similar systems detected with the help of the Fermi gamma-ray observatory. |
| October 10 |
Lee Roberts
(Boston University) |
Schuster Colloquium - The magnetic moment of the muon: does it disagree with the standard model? |
| No abstract available! |
| October 17 |
Phil Marshall
(Oxford) |
Weighing Galaxies |
| Galaxies form and evolve by gravity - the distribution of mass within a
galaxy is arguably it's most important property. The stellar masses of
galaxies can be easily estimated from their luminosity and colour, but lately
we have been finding that, under closer inspection, galaxies weigh more than
they look! I will introduce some new examples of massive galaxies at low
redshift that are acting as strong gravitational lenses, and show how we use
high resolution imaging and deep optical spectroscopy to infer the
gravitational mass of these objects. We can then compare with predictions from
stellar population synthesis models (which require an assumption for the
initial stellar mass function), and when we do, we find some evidence of
non-universality in the IMF. In this way, our samples complement nicely those
galaxies at lower redshift that are measurable with detailed stellar
kinematics mapping alone. Extending projects like these depend on finding more
lenses: I will give a brief glimpse into progress on those searches. Strong
lensing and stellar dynamics enable high accuracy mass measurements of the
cores of galaxies, but their halos remain shadowy, difficult to explore
places. Most of our understanding and intuition about dark matter halos comes
from large N-body simulations: in the last part of my talk I will show how we
can use these to infer directly the properties of halos in the local group of
galaxies, and beyond. |
| October 24 |
Ian McCarthy
(Birmingham) |
Why does the environmental influence on group and cluster galaxies extend beyond the virial radius? |
| It is well known that the properties of galaxies depend in part on their local environment. For example, galaxies in groups and clusters contain less gas and are less likely to be forming stars than their field counterparts. Interestingly, these effects are not limited to the central group/cluster regions, but are shown by recent observations to persist out to several virial radii. To gain insight into the extent and cause of this large-scale environmental influence, we use a suite of high-resolution cosmological hydrodynamic simulations to analyse galaxies around simulated groups and clusters of a wide range of mass. In agreement with the observations, we find a systematic depletion of both hot and cold gas and a decline in the star forming fraction of galaxies as far out as ~5 r200 from the host centre. While a substantial fraction of these galaxies are on highly elliptical orbits and are not infalling for the first time (~50 per cent at 2 r200, independent of host mass) or are affected by 'pre-processing' (~20 per cent of galaxies around groups, increasing to ~50 per cent around a massive cluster), even a combination of these indirect mechanisms does not fully account for the environmental influence, particularly in the case of the hot gas content. Direct interaction with an extended gas `halo' surrounding groups and clusters is shown to be sufficient to strip the hot gas atmospheres of infalling galaxies out to ~5 r200. We show that this influence is highly anisotropic, with ram pressure along filaments enhanced by up to a factor of 100 despite significant co-flow of filament gas and galaxies. We briefly discuss the implications for semi-analytic models of galaxy formation, which presently ignore these effects. |
| October 31 |
— |
Internal Symposium |
| November 7 |
Ruth Gregory
(Durham University) |
Schuster Colloquium - Detecting extra dimensions with cosmic strings? |
| No abstract available! |
| November 14 |
Jay Farihi
(Leicester) |
Archaeology of Extrasolar, Terrestrial Planetary Systems |
| Asteroids, or minor planets, are leftover building blocks of the terrestrial planets, and the largest of these (i.e. Ceres, Vesta, Pallas) are best described as intact planetary embryos. In the Solar System, we indirectly measure their composition by studying meteorites. Over the last several years, evidence has accumulated that strongly indicates we are witnessing metal-rich debris disks that result from the tidal destruction of large asteroid analogs at white dwarf stars. Analogous to the rings of Saturn, these closely-orbiting disks gradually fall onto the star and contaminate the otherwise pure H or He atmosphere. The white dwarf thus distills the planetary fragments into their constituent elements, and provides powerful insight into the mass and chemical structure of the planetary matter, including the potential to identify water. These studies provide information that at present can be acquired no other way: the frequency and bulk chemical composition of terrestrial planetary bodies around other stars. I will present work to date using this novel approach to the study of exo-terrestrial planetary debris. Currently, there appear to be basic similarities between the composition of Solar System asteroids and extrasolar asteroids, and a few cases where differentiated parent bodies are indicated.
|
| November 28 |
Stuart Lumsden
(Leeds) |
Massive Star Formation in the Milky Way |
| The Red MSX Source Survey is designed to find the
massive, mid infrared emitting protostars in our galaxy. I will discuss the key
results from the
survey and how it impacts on our understanding of massive star formation,
as well as why it is still relevant in the era of Herschel. |
December 5
(2:30pm) |
Joanna Haigh
(Imperial) |
Schuster Colloquium
- The
role of the Sun
in climate change |
|
To distinguish natural from anthropogenic causes of climate change we need to quantify and understand any effects resulting from changes in
the Sun. I will outline what is known about variations in solar output and review the evidence for solar influences on climate over a range
of timescales. When the Sun is more active we have found that the response in temperature is not warming in the tropics, as might be
anticipated, but mainly in mid-latitudes, along with a weakening and poleward shift of the jet streams and storm-tracks. Using climate
models we have shown that an important factor driving this response is the absorption in the stratosphere of solar UV radiation, and we have
identified a dynamical coupling mechanism which transfers a solar signal from the stratosphere to the atmosphere below. Recent
satellite measurements have suggested that the solar spectrum has been behaving in a strange and unexpected way. The talk will finish with a
discussion of the implications of these spectral variations for climate change. |
December 5
(4:00 pm) |
Siddharth Malu
(IIT, Indore, India) |
18 GHz observations of cluster mergers |
| Collisions between clusters of galaxies are the most
energetic events in the universe, releasing ~10^55 J of energy, and are sources of synchrotron radiation as Radio Halos and Relics. The exact
mechanism of the production of this synchrotron radiation was thought to be understood well in terms of a so-called Primary Acceleration
model, a major feature of which is a "knee" in the spectrum of the relics and halos. Radio Halos and Relics are therefore not usually observed
beyond ~2-3 GHz.
The serendipitous detection of diffuse emission at 18 GHz in the Bullet cluster has brought this framework into question. I will present
results from recent observations of other clusters at 18 GHz, which are sure to create further controversy in this field. The added confusion
of a negative Sunyaev-Zeldovich Effect makes it all the more complex. The most compelling reason for studying these mergers with complex
dynamics is the unique opportunity they provide to probe the effects of MHD turbulence. These observations, and more like them, are currently
our best hope for understanding the complex processes of MHD turbulence.
|
| December 12 |
Richard Battye
(Manchester) |
HI intensity mapping |
| I will introduce intensity mapping using the 21cm line as a new way to measure the matter power spectrum. Such an approach could provide an relatively cheap way to constrain the acceleration of the Universe via the Baryonic Acoustic Oscillations. I will then describe the single dish concept, called BINGO, being developed within the JBCA to perform an intensity mapping survey. |
| January 16 |
Ettore Carretti
(CSIRO) |
S-PASS and the Giant Magnetised Outflows from the Centre of the Milky Way
|
| The S-band Polarization All Sky Survey (S-PASS) has mapped the polarized radio emission of the entire southern sky at 2.3 GHz with the Parkes Radio Telescope. Aimed at overcoming the depolarization issues of previous surveys taken at lower frequencies (1.4 GHz), S-PASS has unveiled the diffuse polarized emission down to the Galactic disc revealing new and surprising large scale structures. The scientific results that are being obtained are diverse and cover opposite ends of the astrophysics research. In this talk I'll focus on two huge lobes, giant magnetised outflows we have discovered to come out from the Centre of the Milky Way and that are the radio polarized counterpart of the Fermi Bubbles. Extended for some 120 deg in sky, our analysis tells these are star-formation driven outflows bringing a massive magnetic energy of a few 10^55 erg and a strong magnetic field from the compact star formation area orbiting the Galactic Centre out into the Galactic Halo. We also find three ridges on the outflow surface that, we suggest, are record of the star formation activity of the Galactic Centre area of the last ~10 Myr. |
| January 30 |
Jeronimo Bernard-Salas
(IAS) |
Circumstellar and Interstellar Fullerenes |
| Fullerenes are large molecules made of carbon arranged in a spherical or ellipsoidal configuration. These molecules were discovered in laboratory experiments aimed at understanding the formation of long carbon chains in the circumstellar environment of carbon stars. Recently, we reported the first detection of fullerenes (C60, C70) in space, specifically in Tc1, a young planetary nebulae (PNe). Once injected into the ISM these stable species survive, and are thus probably widespread in the Galaxy where they could contribute to the interstellar extinction, heating processes, and complex chemical reactions. Following our discovery, fullerenes have now been detected in a wide range of sources (post-AGBs, PNe, reflection nebula, HII regions, H-poor stars, and YSOs), showing that when conditions are favorable, fullerenes are formed in large quantities. These findings suggest that the circumstellar envelope of evolve stars could be the birthplace of fullerenes. However, their excitation mechanisms - which sets diagnostic value - and formation routes are not yet understood. In this talk I will review our current knowledge on fullerene detection, and I will discuss the pros and cons of the various proposed excitation and formation mechanisms. |
| February 6 |
Rubina Kotak
(Queen's Belfast) |
Supernovae arising from massive stars: current enigmas and future prospects |
| One of the main challenges of current supernova research is to identify
the nature of stars that explode, and link this knowledge to the
observed supernova properties. Nowhere is this problem more urgent than
for the most massive stars in the local and distant Universe. Recent exciting
results have challenged currently accepted paradigms of stellar evolution, and
for these supernovae, ever more exotic scenarios are being proposed.
I will discuss these within the framework of what is currently known about
the progenitors of core-collapse supernovae. Massive star supernovae have an
enormous impact on their surroundings; I will focus on one particular aspect
that this may take, namely, enriching the intergalactic medium with metals
and dust at epochs when the Universe was only a small fraction of its current
age. I will end by speculating on how such studies might evolve in the light of
current and future surveys / facilities.
|
| February 13 |
Alexei Smirnov
(ICPT Trieste) |
Schuster Colloquium - Neutrinos: Flavours of the Invisible |
| Abstract to come |
| Abstract to come |
| February 27 |
Matt Auger
(Cambridge) |
How is dark matter distributed on sub-Mpc scales? |
| Cold dark matter provides an excellent description for the structure of the universe on scales of 10s to 100s of Mpc. However -- in spite of its fundamental importance -- the distribution of dark matter on smaller scales, e.g., in the centres of galaxies and clusters, largely remains unknown. Our ignorance is in part due to the difficulty of making mass measurements on these scales, but also results from degeneracies between the dark matter structure and the mass-to-light ratio of baryons. I will describe how strong gravitational lensing measurements can be used in concert with other mass probes -- including dynamical, weak lensing, and richness-based masses -- to break the stellar/dark mass degeneracy and provide robust constraints on the central dark matter structure of galaxies and poor clusters. Surprisingly, the inferred stellar mass-to-light ratio of massive bulges is significantly larger than in galaxy disks, implying a variation in the IMF from hot spheroidal systems to cold disks. Additionally, galaxy-scale halos may have an excess of central dark matter compared to dark-matter only simulations, while, in contrast with previous studies, cluster halos are consistent with scaling relations from dark matter simulations. |
| March 6 |
Robert Crittenden
(Portsmouth) |
The Intrinsic Non-Gaussianity of the Microwave Background |
| Abstract to come |
| March 13 |
Sarah Bridle
(Manchester) |
Schuster Colloquium - Seeing the Invisible: Observing the Dark Side of the Universe |
| It seems that most of the universe is made up of mysterious ingredients which we cannot see directly. I will describe "gravitational lensing", the bending of light by gravity, which is predicted by Einstein's General Relativity. The dark components of the universe do not emit or absorb light, but do exert a gravitational attraction, and it turns out that gravitational lensing is one of the most promising methods for finding out more about them. This is very similar to looking through a bathroom window at street lamps outside, and using the distorted images to learn about the patterns in the glass. I will describe the recently started Dark Energy Survey which will observe shapes and approximate distances to 300 million galaxies over one eighth of the entire sky. |
| March 20 |
John Brown
(Glasgow) |
Supersonic Snowballs in Hell - The Physics of Sun-Plunging Comets |
| Bombardment of young planets by large 'minor' bodies (rocky asteroids and dusty snowball comets)
played a major role in the early solar system and has been invoked as the source of
earth's water and of some species extinctions. Planetary impacts continue to this day
with at least 3 easily visible Jupiter impacts having occurred since 1994 and a sizeable
impact in Siberia (Tunguska) in 1910. Besides the threat they pose, these objects are of interest in being composed of primordial solar system matter.
The first space observation of a smallish comet falling irreversibly 'into' the sun was made by spaceborne white light coronagraph ~ 1980. Though first thought to be very rare, these 'sun-grazing' comet destructions are now known to occur almost daily. Surprisingly the theory even of the physical regimes of destruction of these giant (10-1000 metre) supersonic (600 km/sec) snowballs in the Hellish near-sun regime has only very recently been published (Brown et al. 2011, A&A 535, A71) and the first actual destruction in the inner solar atmosphere (as opposed to non-re-emergence in coronagraphs of r>> Rsun) was only made (in the UV) in July 2011 by the Solar Dynamics Observatory SDO launched in 2010 (Schrijver, Brown et al 2012 Science 335,324). In December 2011 SDO and other observatories saw the largish sungrazer Comet Lovejoy just survive its skim over the sun at less than 1.2 solar radii
I will summarise the background to, main features of, and future directions in this emerging new branch of comet and solar science involving the interaction of a supersonic cold solid state body with a hot hydrogen plasma 10^8-10^16 times less dense. The dominant process of mass loss of the icy nucleus will be shown to be sublimation by solar radiation , ablation by solar atmospheric bombardment. or explosion by atmospheric ram pressure, depending on the nucleus mass and perihelion distance. The first (SDO event) regime involves a relatively gentle 'fizzle' over minutes to hours while the latter two (yet to be seen directly) are impulsively explosive (< 10 sec) and should produce phenomena somewhat like magnetic solar flares,including multi-wavelength bursts and 'sunquake' waves in the photosphere though with highly non-solar element abundances and spectral signatures. Because of the rapid exponential increase of solar density with depth, even the most massive comets ever mooted (~1e19 kg ~ 1000 Hale-Bopps)are destroyed well above the photosphere where the collisional heating is 100,000 times sunlight. The superflare caused by such a body would have major terrestrial and human consequences |
| March 27 |
— |
Easter |
| April 3 |
— |
Easter |
| April 10 |
— |
Easter |
