Cosmic Acceleration: A Natural Remedy For Horizon and Flatness Problems

By assuming that the recently found cosmic acceleration is a genuine and ever present effect, we show that, the resultant modified Friedman model is free from the horizon and flatness problems; and there is no need to invoke the additional “inflationary” initial phase as a separate ingredient.

Gravitational Lensing Studies of High Resolution Cluster Simulations

In our ongoing work, we use high resolution cluster simulations to study gravitational lensing. These simulations have a softening length of 0.7 h-1 kpc and a particle mass of 4.68 × 107M⊙ (Springel 1999). Questions that can be addressed include the accuracy with which substructure on various scales can be recovered using the information from lensing. This is very important in determining the power of lensing in studying the evolution of cluster substructure as a function of redshift. We briefly consider how a weak lensing non-parametric reconstruction technique and the Map-statistic can be applied to the simulations.

Foreground Separation Methods for Satellite and Balloon Experiments

A combined technique using the maximum-entropy method (MEM) and the mexican hat wavelet (MHW) to separate and reconstruct the physical components of the microwave sky is presented. We apply this method to simulated observations by the ESA Planck satellite in small patches of the sky. The reconstructed maps of the CMB and foregrounds are improved as compared to those obtained with MEM on its own. Moreover, more accurate point source catalogues are produced at each observing frequency. This technique may also be extended to deal with other multifrequency CMB experiments, including all-sky data.

The Galaxy Environment of Quasars in the z ⋍ 1.3 Clowes-Campusano Large Quasar Group

We report significant associated clustering in the field of a z = 1.226 quasar from the Clowes-Campusano LQG in the form of both a factor ˜ 11 overdensity of I - K > 3.75 galaxies, and red sequences of 15-18 galaxies at I - K ⋍ 4.3, V - K ⋍ 6.9 indicative of a population of massive ellipticals at the quasar redshift. The quasar is located between two groups of these galaxies, with further clustering extending over 2-3 Mpc. A band of V - I < 1 galaxies bisects the two groups of red sequence galaxies, and we suggest that the merging of these two groups has triggered both this band of star-formation and the quasar.

The Very Small Array: Observations and Latest Results

The Very Small Array (VSA) is a unique interferometric telescope operating at 33 GHz at Tenerife. It has the ability to measure fluctuations in the CMB over a large range of angular scales by means of three main array configurations: compact, extended and super-extended. These angular scales correspond to the multipole range ℓ = 150 —2500. Here we present new results from further observations of the extended array (February 2002 - June 2003). We cover ℓ-values up to ℓ ∼ 1600, thus doubling the ℓ-range of WMAP. The resulting power spectrum in the ℓ-range 800 – 1600 has very low noise coupled with good ℓ-resolution (Δℓ ∼ 80). Furthermore, the use of independently tracking aerials along with the dedicated source subtraction baseline allows unprecedented control of systematics. The latter is essential, since discrete sources are the dominant foreground at these angular scales. These measurements over larger ℓ-ranges are important in confirming the present cosmological paradigm and breaking degeneracies in the extraction of cosmological parameters.

Imaging the Cosmic Microwave Background with the Arcminute Cosmology Bolometer Array Receiver

The Arcminute Cosmology Bolometer Array Receiver (Acbar) is a multifrequency millimeter-wave receiver optimized for observations of the Cosmic Microwave Background (CMB) and the Sunyaev-Zel'dovich (SZ) effect in clusters of galaxies. Acbar was installed on the 2.1 m Viper telescope at the South Pole in January 2001 and the results presented here incorporate data through July 2002. The power spectrum of the CMB at 150 GHz over the range ℓ = 150 — 3000 measured by Acbar is presented along with estimates for the values of the cosmological parameters within the context of ΛCDM models. The inclusion of ΩΛ greatly improves the fit to the power spectrum. Three-frequency images of the SZ decrement/increment are also presented for the galaxy cluster 1E0657–67.

Amplitude-Phase Analysis of Cosmic Microwave Background Maps

We propose a novel method for the extraction of unresolved point sources from CMB maps. This method is based on the analysis of the phase distribution of the Fourier components for the observed signal and unlike most other methods of denoising does not require any significant assumptions about the expected CMB signal. The aim of our investigation is to show how, using our algorithm, the contribution from point sources can be separated from the resulting signal on all scales.

The TopHat Cosmic Microwave Background Anisotropy Experiment

We have developed a balloon-borne experiment to measure the Cosmic Microwave Background Radiation anisotropy on angular scales from ˜50° down to ˜20′. The instrument observes at frequencies between 150 and 690 GHz and will be flown on an Antarctic circumpolar long duration flight. To greatly improve the experiment performance, the front-end of the experiment is mounted on the top of the balloon. With high sensitivity, broad sky coverage, and well-characterized systematic errors, the results of this experiment can be used to strongly constrain cosmological models and probe the early stages of large-scale structure formation in the Universe.

Constraining Galaxy Formation Epoch

Pinning down the ages of high redshift galaxies is the most direct way of constraining the galaxy formation epoch. There has been a debate on the age of LBDS 53W091, a red galaxy at z=1.5. The discrepancy in the age estimates of various groups is due to the difference in the population synthesis model. However, there is generally a good agreement among popular models. Polishing the models and assessing their internal uncertainties are crucial in the analysis of high redshift galaxies.

X-ray Cluster Large Scale Structure and Cosmology

We outline the main arguments in favor of cosmological X-ray surveys of galaxy clusters. We summarize recent advances in our understanding of cluster physics. After a short review of past surveys, we present the scientific motivations of the XMM Large Scale Structure survey. We further illustrate how such a survey can help constrain the nature of the dark energy as well as cluster scaling law evolution, i.e. non-gravitational physics.