Search Talks

The Red-Sequence Cluster Survey (RCS2) is a 1000-square-degree, multi-color imaging survey carried out using MegaCam on the 3.6m CFHT which is optimized for the search of galaxy clusters with 0.15

The largest structures in the Universe -- Superclusters of Galaxies -- range in size from a few Mpc to the 'Great Walls' scale of hundreds of Mpc. What is the shape of these large structures -- are they filamentary in nature or are they flattened two-dimensional 'pancakes'? How do they form and evolve? Superclusters are typically dominated by clusters of galaxies, systems that serve as one of the most powerful tools in cosmology. What is the shape of clusters -- are they spherically symmetric or are they elongated? Are they aligned with each other on large scales? I present results that answer these fundamental questions, revealing the predicted shape and evolution of the large-scale structure in the Universe in the current popular cosmology. We show that the shape of clusters provides an interesting new tool in constraining cosmology, as well as provides clues to the formation and evolution of large-scale structure.

Yes, that's indeed where it happens. These pictures are not ordinary pictures but come with category-theoretic algebraic semantics, support automated reasoning and design of protocols, and match perfectly the developments in important areas of mathematics such as representation theory, proof theory, TQFT & GR, knot theory etc. More concretely, we report on the progress in a research program that aims to capture logical structures within quantum phenomena and quantum informatic tasks in purely diagrammatic terms. These picture calculi are faithful representations of certain kinds of monoidal categories, and structures therein. However, the goal of this program is partly to `release' these intuitive languages (or calculi) from their category-theoretic underpinning, and conceiving these pictures as mathematical entities in their own right. In this new language one is able to model and reason about things such a complementary observables, phase data, quantum circuits and algorithms, a variety of different quantum computational models, hidden-variable models, aspects of non-locality, and reason about all of these in terms of intuitive diagram transformations. Some recent benchmarks are the diagraamatic computation of quantum Fourier transform due to Duncan and myself, a purely diagrammatic proof of the no-cloning theorem due to Abramsky, and a categorical characterisation of GHZ-type non-locality due to Edwards, Spekkens and myself. For informal introductions we refer to: [1] Kindergarten quantum mechanics. http://arxiv.org/abs/quant-ph/0510032 [2] Introducing categories to the practicing physicist. http://arxiv.org/abs/0808.1032 For recent more advanced developments we suggest: [3] Selinger: Dagger compact closed categories and completely positive maps QPL\'05 http://www.mathstat.dal.ca/~selinger/papers.html#dagger [4] Coecke, Pavlovic, Vicary: A new description of orthogonal bases. http://arxiv.org/abs/0810.0812 [5] Coecke, Paquette, Perdrix: Bases in diagrammatic quantum protocols http://arxiv.org/abs/0808.1029 [6] Coecke, Duncan: Interacting quantum observables. ICALP\'08. http://www.springerlink.com/content/y443214116h76122/ [7] Coecke, Edwards: Toy quantum categories. QPL\'08. http://arxiv.org/abs/0808.1037

In 2001 we made an unexpected discovery of a very bright SZ spot toward the X-ray luminous cluster RXJ1347-1145, which was significantly displaced from the center of the cluster's gravitational potential. One of the possible interpretations is that this spot is a signature of a violent merger in this cluster. This sypothesis has been confirmed by the subsequent Chandra X-ray observations. In this talk I will report on recent results from our follow-up observation of XJ1347-1145 with Suzaku X-ray telescope. Our studies show that the SZ effect, when it is mapped with a fine angular resolution of order 10 arc-seconds, provides a powerful probe of violent cluster mergers.

The coming era of large, multi-wavelength surveys motivates and, ultimately, will inform a multivariate statistical framework describing cluster properties in relation to underlying halo mass and redshift. In this talk, I will present work at Michigan that focuses on a multivariate Gaussian likelihood approach to this problem, and includes empirical studies using optical and X-ray observations of the SDSS maxbcg sample as well as a computational program using Gadget resimulations of the Millennium Simulation with preheated gas dynamics. I will show evidence from the models that a combination of fgas measurements from X-rays along with Ytot from thermal SZ can constrain mass at the rms level of 4%.

The Sunyaev Zel'dovich effect is expected to be one of the major contaminants at arcminutes scales in CMB analysis. I will present a method we developed at IAS to quantify the biases on parameter determination when any additive signal is not taken into account in the analysis. I will then present an application of this method in order to quantify the biases induced on cosmological parameter estimation when the SZ residuals are not properly taken into account in the analysis of the CMB. The important biases that would result from such a treatment encouraged us to developed a joint analysis of the CMB plus SZ signal that consists in determining the cosmological parameters fitting both signals. I will compare various methods to carry out such an analysis and will emphasize that only the coherent method that takes into account the dependency of the SZ spectrum with all the cosmological parameters allows an unbiased determination of the parameters. I will conclude by discussing the improvement on parameters error bars du to the extra information included in the SZ power spectrum and by pointing out the difficulties that our incomplete understanding of the intra cluster gas physics can set.