Joint Cosmology Seminar

The format for the first meeting of this academic year's joint cosmology seminar series is the following: Everyone is requested to bring along one viewgraph outlining their research interests and will be given a minute+ to introduce themselves and present it. The one viewgraph rule will be strictly enforced. The idea is to kick-off the series by allowing us to know who-is-who, what we all do and where we can be found in the Cambridge Cosmology jungle. Please do attend even if you dont feel like presenting. First year graduate students are particularly welcome (they need not feel compelled to say anything beyond simply introducing themselves) since this might be an easy way to efficiently find out about current research activities at the DAMTP, IoA and MRAO.

The redshift-independence of the Sunyaev-Zel'dovich (SZ) effect makes it an excellent tool for investigating structure at high redshift. This talk will include a brief introduction to SZ observing, and a presentation of some recent results from studies of distant clusters.

My talk will contain a review of the components of Galactic emission, which together with other CMB foregrounds could ultimately limit the significance and accuracy of observed CMB anisotropy, the power spectrum and non-Gaussian features. As an example of the difficult process of identifying foreground components I will present our latest work on Tenerife data investigating whether a new Galactic component, spinning dust, is required.

Our knowledge of the galaxy population in the local Universe is reasonably complete for bright high luminosity galaxies, but is poor for faint low luminosity galaxies, particularly since these small galaxies have low surface brightnesses. The properties of these galaxies are important for cosmology since they have such large dark matter fractions, at least 99% in some cases. I review the current observational situation and describe new observations of dwarf galaxies and outline the implications for cosmology.

Recently, several groups, e.g., Ferreira, Magueijo & Gorski (bispectrum analysis), have reported detection of a non-Gaussian signal in the COBE-DMR publicly available maps. In this talk I will report results from a recent study carried out by A.J. Banday, K.M. Gorski and myself aimed at examining whether the source of the detected non-Gaussianity in the COBE-DMR signal is of cosmological origin. Our study has resulted in a plausible resolution to the problem, tracing the origin of the signal to a systematic effect in the data.

Neutrinos that decay leave an imprint on the cosmic microwave background. I discuss the CMB anisotropies for the full decaying neutrino parameter space. I then show how to use two complementary approaches to investigate the ability of future experiments like MAP and Planck to probe decaying neutrino physics. In the first approach, decaying neutrino parameters are added to the set of cosmic parameters, while in the second decaying neutrino models are distinguished from a set of standard cosmological models. In conclusion, I will show that MAP and Planck may be sensitive to eV-scale neutrinos, as long as their lifetimes are longer than the age of the universe at recombination.

ALMA will be the largest observatory covering the 30-900 GHz range. It will have excellent Fourier plane coverage, and very high sensitivity. A brief overview of the ALMA project will be given, followed by an outline of its potential cosmological applications. These include measuring primordial anisotropies on scales smaller than 10-20 arcmin, foreground subtraction for Planck, SZ imaging, and detecting dust and gas out to z=5 and beyond.

The well-being of experimental submillimetre-wave astronomy is intimately linked to our ability to produce extremely sensitive detectors and instruments. The technology for this wavelength range is changing rapidly, and during the next 10 years considerable advances will take place. High and low-resolution spectroscopy, and large-format widefield coherent and incoherent imaging will become common-place. In the talk I will outline the nature of some of the developments that are taking place, and describe plans for establishing a submillimetre-wave astronomical detector laboratory at the Cavendish.

Numerical hydrodynamical simulations have successfully predicted many of the observed properties of the Lyman-Alpha forest. Most of the comparisons to date, however, have been based on either global properties of the measured spectra or heterogeneous comparisons between simulated and published Voigt line parameter distributions. We use numerical simulations to predict the spectral properties of measured Lyman-Alpha forest spectra, for which the Voigt line statistics are derived in a consistent manner. The resulting agreement between the predicted and measured distributions suggests that observations of the Lyman-Alpha forest may be used as a new means to distinguish between competing cosmological models.

How did the Universe begin? Inflation does not answer this question so much as sidestep it. Observational progress towards confirming simple theories of quantum fluctuations is tremendously exciting, For theorists the challenge it poses is that we develop a proper theory of quantum gravitational effects. The first talk will review recent attempts developing the Euclidean approach to quantum gravity. The second talk will explain progress we have made in determining the negative modes about cosmological instantons. This work sheds significant light on the interpretation of cosmomological solutions, as well as on how fluctuations should be quantised beyond leading order.

One of the most serious contaminants of the data for microwave-background mapping instruments is the emission from foreground sources - radio galaxies and quasars. It is not possible to look up the sources in a catalogue - there are none at the high frequencies involved and in any case many of the sources are highly variable. To solve this problem for the VSA, we use a two-stage process: we survey the regions of sky at 15 GHz with the Ryle Telescope, and then make a measurement at 30 GHz with the source-subtractor elements of the VSA itself to obtain properly concurrent data at the right frequency. I shall describe the observing and reduction process, which uses the Ryle Telescope in a mode quite different from that envisaged in its original design.

Point source removal poses a difficult problem in analysis of Planck data, since each source has a unique frequency spectrum and so standard multifrequency algorithms fail. Nevertheless, by combining the use of the continuous wavelet transform and a maximum-entropy algorithm, simulations suggest that it is in fact possible to reduce point source contamination of the CMB signal to an acceptably low level. As a by-product this combined technique also allows the construction of point source catalogues from Planck observations.