The Sunyaev-Zel'dovich e ect causes a change in the apparent brightness of the Cosmic Microwave Background Radiation towards a cluster of galaxies or any other reservoir of hot plasma. Measurements of the e ect provide distinctly di erent information about cluster properties than X-ray imaging data, while combining X-ray and Sunyaev-Zel'dovich e ect data leads to new insights into the structures of cluster atmospheres. The e ect is redshift-independent, and so provides a unique probe of the structure of the Universe on the largest scales. The present review discusses the theory of the Sunyaev-Zel'dovich e ect and collects published results for many clusters, presents the overall conclusions that may bedrawn from the detections so far, and discusses the prospects for future research on the Sunyaev-Zel'dovich e ects.Subject headings: Sunyaev-Zel'dovich E ect; Clusters; Microwave Background Radiation Astrophysical ContextCompton scattering is one of the major physical processes that couples matter and radiation. Its importance is often stressed in highly relativistic environments where large energy transfers occur: for example, in the synchrotron self-Compton process that may beresponsible for much of the X-radiation from active galactic nuclei (e.g., Fabian et al. 1986). However, the Compton process also has observable consequences in low-energy environments, where small energy transfers occur. The Sunyaev-Zel'dovich e ect, which arises from the scattering of electrons in clusters of galaxies on the cosmic microwave 1 Also Smithsonian Institution Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138, USA { 2 { background radiation eld, is perhaps the most important astrophysical example. The e ect provides a cosmological probe, it has been used to measure the properties of gas in clusters of galaxies, and it has been discussed as a means of measuring the motions of clusters of galaxies and hence studying the evolution of structure in the Universe.The purpose of this review is to provide a comprehensive introduction to the SunyaevZel'dovich e ect. I aim to provide both a theoretical treatment that can befollowed by non-specialists, and an introduction to the observation of the e ect with a critical review of data in the literature. The latter is more di cult today than it would have been ve years ago because of the rapid increase in the number of papers on the Sunyaev-Zel'dovich e ect, and the improvement i n t h e quality o f t h e results that are being gained.

The Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope provides an unprecedented opportunity to study gamma-ray blazars. To capitalize on this opportunity, beginning in late 2007, about a year before the start of LAT science operations, we began a large-scale, fast-cadence 15 GHz radio monitoring program with the 40-m telescope at the Owens Valley Radio Observatory (OVRO). This program began with the 1158 northern (δ > −20 • ) sources from the Candidate Gammaray Blazar Survey (CGRaBS) and now encompasses over 1500 sources, each observed twice per week with about 4 mJy (minimum) and 3% (typical) uncertainty. Here, we describe this monitoring program and our methods, and present radio light curves from the first two years (2008 and 2009). As a first application, we combine these data with a novel measure of light curve variability amplitude, the intrinsic modulation index, through a likelihood analysis to examine the variability properties of subpopulations of our sample. We demonstrate that, with high significance (7-σ), gamma-ray-loud blazars detected by the LAT during its first 11 months of operation vary with about a factor of two greater amplitude than do the gamma-ray quiet blazars in our sample. We also find a significant (3-σ) difference between variability amplitude in BL Lacertae objects and flat-spectrum radio quasars (FSRQs), with the former exhibiting larger variability amplitudes. Finally, low-redshift (z < 1) FS-RQs are found to vary more strongly than high-redshift FSRQs, with 3-σ significance. These findings represent an important step toward understanding why some blazars emit gamma-rays while others, with apparently similar properties, remain silent.

Gravitational lensing is a powerful astrophysical and cosmological probe and is particularly valuable at submillimeter wavelengths for the study of the statistical and individual properties of dusty star-forming galaxies. However, the identification of gravitational lenses is often time-intensive, involving the sifting of large volumes of imaging or spectroscopic data to find few candidates. We used early data from the Herschel Astrophysical Terahertz Large Area Survey to demonstrate that wide-area submillimeter surveys can simply and easily detect strong gravitational lensing events, with close to 100% efficiency.

We present a Chandra and XMM-Newton study of X-ray emission from the lobes of 33 classical double radio galaxies and quasars. We report new detections of lobe-related X-ray emission in 11 sources. Together with previous detections, we find that X-ray emission is detected from at least one radio lobe in $75% of the sample. For all of the lobe detections, we find that the measured X-ray flux can be attributed to inverse Compton scattering of the cosmic microwave background radiation, with magnetic field strengths in the lobes between 0.3B eq and 1.3B eq , where the value B eq corresponds to equipartition between the electrons and magnetic field, assuming a filling factor of unity. There is a strong peak in the magnetic field strength distribution at B $ 0:7B eq . We find that more than 70% of the radio lobes are either at equipartition or electron dominated by a small factor. The distribution of measured magnetic field strengths differs for narrow-and broad-line objects, in the sense that broad-line radio galaxies and quasars appear to be further from equipartition; however, this is likely to be due to a combination of projection effects and worse systematic uncertainty in the X-ray analysis for those objects. Our results suggest that the lobes of classical double radio sources do not contain an energetically dominant proton population, because this would require the magnetic field energy density to be similar to the electron energy density rather than the overall energy density in relativistic particles.

We report the detection of a diffuse radio halo source in the hottest known cluster of galaxies 1E0658-56 (RXJ0658-5557). The radio halo has a morphology similar to the X-ray emission from the hot intracluster medium. The detection of such a strong radio halo in such a hot cluster is further evidence to the link between X-ray temperature and cluster-wide radio halos. We describe a new model for the origin of cluster-wide radio halo sources involving a direct connection between the X-ray emitting thermal particles and the radio emitting relativistic particles.