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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. |
