CITA continues its long tradition of physical cosmology through the direct interactions of theories with observations. CMB analysis has been refined at CITA, and several of the most important data sets, including Boomerang, CBI and Amiba have key analyses carried out at CITA. A recent addition to the effort has been weak lensing analysis. CITA's expertise and computing infrastructure continue to drive a strong analysis and simulation effort, including large scale parallel N-body and hydrodynamics.
Iliev has performed, in collaboration with Paul Shapiro (University of Texas at Austin) and Alejandro Raga (UNAM, Mexico City), the first realistic radiation-hydrodynamical simulations of the photoevaporation of cosmological minihalos by global I-fronts during the epoch of reionization. They have studied this complex process in detail, deriving many important quantities like the evaporation timescale, the total number of ionizing photons required for completion, along with some observable consequences. For the collapsed fraction in minihalos expected during reionization, they found that this process can add up to 1 photon per total atom in the universe to the requirements for completing reionization, potentially doubling the minimum number of photons required to reionize the universe.
Ilian Iliev, in collaboration with Evan Scannapieco (KITP,UCSB) and Paul Shapiro studied the influence of small-scale gas inhomogeneities due to structure formation on the propagation of the global I-fronts during reionization using semi-analytical method which incorporates also the effects of infall and nonlinear clustering of halos (halo bias). The inhomogeneities studied included both minihalos, which are generally able to self-shield some of their gas, and lower-density structures (e.g filaments) which are unable to self-shield but increase the overall recombination rate in the IGM. They found that that both IGM clumping and minihalos have significant impacts on the propagation of the global I-fronts, slowing them down and extending reionization in time and thus can help in understanding the recent observations by Wilkinson Microwave Anisotropy Probe, which point to an early and extended reionization epoch.
Hoekstra started the Canadian Cluster Comparison Project with Babul (Victoria) and other CoI's across Canada. This program aims to obtain accurate masses for a sample of 60 X-ray luminous galaxy clusters which will enable one of the most detailed studies of the hot intracluster gas, leading to a better understanding how the baryons in clusters evolve. Hoekstra retrieved and analysed archival CFHT data for 20 clusters and the remaining clusters will be observed with Megacam on CFHT. With Sievers, Hoekstra is imaging a subset of these clusters using CBI which will yield useful measurements of the SZ effect.
Hoekstra continued work on the CFHTLS in close collaboration with van Waerbeke (IAP, now UBC) building on a fruitful collaboration on the VIRMOS survey. The latter survey was reanalysed and Hoekstra was able to significantly reduce the level of systematics in the cosmic weak lensing shear signal, resulting in the most accurate measurement to date. With Vale and White (Berkeley) and van Waerbeke, Hoekstra investigated some effects of imperfect calibrations on cosmic shear measurements.
Hoekstra continued work on the RCS, using a new photometric redshift catalog created by Hsieh (Taiwan). With Yee (Toronto) and Gladders (Pasadena) Hoekstra studied the baryon fraction in galaxies and the virial mass as a function of luminosity. This study suggests that late type galaxies are significantly more efficient in transforming baryons into stars, compared to early type galaxies.
Lewis studied vector modes and their observational signature in the CMB. There is a regular primordial mode with a potentially interesting observational signature in the CMB polarization, for which he computed the theoretical predictions. Vector modes are also sourced by magnetic fields, and he computed numerically the effect of primoridal inhomogeneous magnetic fields on the CMB power spectra, identifying some new effects and problems with previous results.
There was further work refining the widely used Markov Chain Monte Carlo code CosmoMC for parameter estimation, developing new efficient proposal distributions and methods for handling 'fast' and 'slow' parameters. He organised a productive cross-disciplinary workshop with Radford Neal (Toronto): some of Neal's ideas were incorporated into CosmoMC. With Bond and Contaldi the code was applied to parameter forcasting for WMAP and Planck.
Lewis continued studying CMB lensing, improving on a public simulation code and testing the CosmoMC parameter estimation pipeline on lensed CMB skies. He identified poor accuracy in the widely used first-order series expansion in the lensing potential, sufficient to bias parameter constraints with Planck. This lead on to work in late 2004 with Anthony Challinor (Cambridge) on a new improved calculation.
Majumdar and his collaborators have carried out work on using the cosmological distribution of clusters of galaxies and their imprint on the Cosmic Microwave Background (CMB), through the Sunyaev-Zel'dovich effect (SZE). It was first shown by Majumdar and Mohr (UIUC) how strong constraints on the equation of state of dark energy can be obtained from upcoming cluster surveys by a combination of cluster redshift distribution and cluster power spectrum even in the presence of cosmology-gas physics degenaracies. Other than the detecting clusters with SZE, the rms fluctuations of the arc-min scale CMB from the SZE from clusters can be used to constrain cosmological and cluster parameters. To succesfully do so, one needs to understand the impact of point sources for these upcoming SZE surveys. This crucial input for the upcoming surveys was studied by White (Berkeley) and Majumdar where it was shown that IR sources can be significant source of additional noise. Apart from doing cosmology with clusters, the SZE power spectrum from clusters can be used to determine the state and evolution of cluster gas physics.
Diego (MIT) and Majumdar have shown how one can combine cluster SZE counts with clusters SZE rms fluctuations to mitigate the strong influence of cosmology in order to study cluster physics.
Majumdar has been involved in an ongoing project to use RCS clusters to study cosmology. In addition, Majumdar and Cox (UVIC) have a major ongoing project to build up a Markov Chain Monte Carlo analysis code for cluster surveys.
Majumdar has been involved in studying the dark mater halo of our Galaxy. To do so he and his collaborators (Cowsik, Ratnam & Bhattacharjee (IIAP, Bangalore)) have looked at the effect of the baryonic component of our Galaxy on the phase-space structure of the dark matter halo. This has been used to put limits on the extent of the halo and the dark matter dispersion velocity in our Galaxy.
As part of the Canadian contribution to Planck (an European Space Agency satellite devoted to the study of the CMB in the sub-millimeter), CITA develops the Quick Look Analysis (QLA) software that will be used for the visualization and analysis of ground calibration and in-flight data. A significant fraction of the activities of M.-A. Miville-Desch\^enes, a Canadian Planck scientific associate, are devoted to the design and development of the QLA, and to the participation to the calibration tests of the High-Frequency Instrument (HFI) in Orsay, France.
M.-A. Miville-Desch\^enes worked on the difficult problem of separating Galactic, extra-galactic and cosmological signals in diffuse regions of the sky (a problem known as ``component separation''). He is involved in several projects devoted to the observation of very low column density HI clouds, to characterize their properties in the far-infrared and in the sub-millimeter and to evaluate the possibility of using 21 cm observations to remove foreground emission. These observations are done with the DRAO (Penticton, Canada) and GBT (Virginia, USA) radio-telescopes, and with Spitzer. This work is done in collaboration with P. Martin (CITA), J. Lockman (NRAO) and the IAS team (France). In collaboration with J.-P. Bernard (CESR, Toulouse), M.-A. Miville-Desch\^enes also developed an all-sky model that allows to predict the emission from every foreground emissions in the Planck bands.
Pen's main research effort was the theoretical, observational and instrumental implications of the epoch of reionization. A major instrumental effort called Primeval Anisotropy Probe (PAST) was launched, headed by Xiang-Ping Wu (National Astronomical Observatories of China), and included Jeff Peterson as a collaborator. The period included 6 trips to western china, and the deployment of several prototypes. First light on the prototype telescope was obtained in March 2004, which has been submitted for publication (astro-ph/0404083). The theoretical work on the field includes papers on the ostriker-vishniac effect with Zhang (Fermilab), and major high redshift simulations by Trac (Toronto) using up to 1500^3 grid cells, and studies of the feasibility of weak gravitational lensing of such high redshift sources.
Sievers, Bond, and Contaldi, along with the CBI collaboration (PI Anthony Readhead, Caltech), made the best measurement to date of the EE polarization spectrum of the Cosmic Microwave Background. This marked the first time that features in the EE spectrum (as opposed to a single overall power level) were used to check the conistency of the EE and TT CMB spectra. This work was featured on the cover of Science. Sievers, with the same collaborators, measured the TT power spectrum of the CMB to an ell of 3500 using the CBI. This work was an extension, using more data, of previous releases and included tighter limits on excess power seen on scales smaller than ell ~ 2000.
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