Cosmology

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.

In 2008, the Atacama Cosmology Telescope began its first full season observing a strip of the southern sky in three millimeter-wave bands. We present preliminary maps at 145 GHz featuring some SZ clusters.

The South Pole Telescope (SPT) is a 10-meter diameter telescope with a 960 element millimeter-wavelength bolometric receiver, which is in the midst of its third season of observations at the South Pole. The SPT has been optimized for measurements of the Sunyaev-Zel'dovich (SZ) effect in galaxy clusters. With this instrument, we are surveying the southern sky to create a mass limited catalog of galaxy clusters out to the epoch of their formation. This program of observations will also produce significant detections of the kinetic SZ effect and weak gravitational lensing of the CMB, a multi-band millimeter-wavelength point source catalog, and images of the SZ effect in known galaxy clusters with unprecedented sensitivity. In this talk, I will discuss the design, construction, and deployment of the SPT telescope and receiver, progress of the observations, and conclude with a discussion of future plans.

As observations of clusters through their SZ imprint on the CMB becomes more routine, it is now feasible to add this signal to the set of observables we use to study galaxy clusters. Using the Sunyaev-Zel'dovich Array (SZA), we are pursuing a variety of programs to investigate the correlation between cluster properties and their SZ signatures. I will present early results from these comparisons. The SZA is also a unique tool for resolved SZ imaging as part of the 23-element CARMA interferometer. I will discuss our initial experiment with heterogeneous array interferometry later this year and the future capabilities of the full array.

"There is considerable uncertainty in the theoretical predictions for the angular power spectrum from the Sunyaev-Zeldovich effect (SZe). The level of precision reached by ACT, SPT, and Planck for measurements of the normalization of the SZe power spectrum, sigma_8, will be limited by the uncertainty in the theoretical models for the angular power spectrum. The uncertainties in the predicted spectrum arise from the complicated physics of the ICM. We have explored these ICM complexities using hydrodynamical simulations in a cosmological setting with several different variants of simulated physics, including cooling and star formation, star formation feedback by galactic winds and supernovae as well as cosmic ray physics. Our statistics were compiled from two independently stacked cluster samples consisting of cosmological box simulations and individual high-resolution cluster simulations. We show that a simple parametrized fit describes averaged ICM pressure profiles sufficiently well and compare this finding to previous hydrostatic models. We find that radiative cooling and the associated star formation is the dominant physical process that modifies our fit parameters for these profiles and the angular power spectrum. "