Many recent estimates of the star formation rate density at high redshift rely on rest-frame ultraviolet (UV) data. These are highly sensitive to dust absorption. Applying a correlation between the far-infrared (FIR) to UV flux ratio and UV color found in local starbursts to galaxy samples out to z ∼ 3, one can account for most of the FIR background. However, the correlation is based on a sample that does not include the most extreme starbursts, Ultra Luminous Infrared Galaxies (ULIGs). Our new UV images of ULIGs show that their FIR fluxes are underpredicted by this correlation by factors ranging from 7 to 70. We discuss how ULIGs compare to the various types of high-z galaxies: sub-mm sources, Lyman Break Galaxies, and Extremely Red Objects.

Observations made using COBE, SCUBA, ISO and MAMBO have provided a reasonable working knowledge of both the intensity of the submm and far-infrared background radiation and the source counts of luminous high-redshift dusty galaxies. However, because there are uncertainties in the background intensity determinations, the samples of detected galaxies are small, and most importantly, their redshift distributions are very incomplete, details of the evolution of dusty galaxies remain unresolved. The next steps forward in the field will be the launches of SIRTF and ASTRO-F, the commissioning of SOFIA and new, more capable ground-based mm/submm-wave cameras - BOLOCAM, SHARC-II and SCUBA-II - the use of ultra-long duration balloon experiments, such as BLAST, the construction of ALMA and the arrival of FIRST, and ultimately the advent of space-borne far-infrared interferometers, such as SPECS. There are also exciting prospects for direct mm/submm-wave CO-line redshift surveys using wide-band spectrographs. Using these new facilities, the number of high-redshift dusty galaxies known will be increased dramatically. Spectroscopy using SIRTF, SOFIA and FIRST will probe the astrophysical processes within these sources in detail, hopefully addressing the open question of the fraction of the counts and background radiation that is generated by the formation of high-mass stars and by active galactic nuclei (AGNs). The spatial and spectral structure of distant dusty galaxies will finally be resolved in detail using ALMA and SPECS.

I review the evidence for cluster mergers from X-ray observations with Einstein and ROSAT. Different techniques to study cluster mergers via X-ray imaging and spectral data, and the current implications of measurements of cluster substructure for Ω0, are briefly discussed.

We discuss two themes from Chandra cluster observations. First, we describe the interaction of buoyant, radio emitting plasma bubbles with the hot intracluster gas. Second we summarize the Chandra observations of “cold” fronts (sharp discontinuities in gas density and temperature) separating cool, denser gas clouds from the hotter intracluster medium.

First spatially resolved spectroscopic observations of the Virgo and Coma clusters made with XMM during the PV phase are presented. The implication for the dynamical state of these clusters are briefly discussed.

An increasing amount of data has revealed that many clusters are very complex systems. Optical analyses show that several clusters contain subsystems of galaxies suggesting that they are still in the phase of relaxation, possibly after a phase of cluster merging. I briefly review the main results about substructure, and the connection between cluster dynamical status and galaxy properties. Useful comparisons with the results derived from X-ray data are also discussed.

The number of known diffuse radio sources in clusters of galaxies (halos and relics) has grown in recent years, making it possible to derive statistical considerations on the physical conditions of these sources and on the properties of related clusters. We will discuss the percentage of clusters with a diffuse source and will show evidence that diffuse sources are associated with X-ray luminous clusters which have undergone recent merger processes.

We will discuss the properties and origins of halos and relics including estimates of the cluster magnetic fields, and present results for a few recently discovered halos and relics. The electrons in the suprathermal high energy tail of the thermal gas distribution are likely to provide the seed particles for acceleration through mergers and turbulences to relativistic energies. These relativistic particles are then responsible for the synchrotron emission of the halos.

The results of a systematic study of substructures in X-ray surface brightness distributions of BCS, NORAS, REFLEX, radio halo, relic, and cooling flow clusters of galaxies based on RASS data are presented. At least 40 percent of the clusters show substructure. Indications for a cluster morphology-density relation are found. The fraction of clusters with substructure seems to be higher for halo and relic clusters and lower for clusters with cooling flow signature.

The properties of radio sources in and outside of Abell clusters are reviewed. The properties of sources in and out of Abell clusters are shown to be surprisingly similar. However, sources in dense cluster cores do not fit this pattern and, as in Virgo A (M87), have a significant, sometimes dominant input of energy into the “cooling core” environment.

We now know that the plasma in clusters of galaxies is magnetized, at strong levels in some regions. It follows that the dynamics of the cluster plasma is more complex than has been thought up to now.

The strong activity of radio galaxies should have led to a nearly ubiquitous presence of fossil radio plasma in the denser regions of the inter-galactic medium as clusters, groups and filaments of galaxies. This fossil radio plasma can contain large quantities of relativistic particles (electrons and possibly protons) by magnetic confinement. These particles might be released and/or re-energized under environmental influences as turbulence and shock waves. Possible connections of such processes to the formation of the observed sources of diffuse radio emission in clusters of galaxies (the cluster radio halos and the cluster radio relics) are discussed.

Numerical simulations of cluster mergers reveal many characteristics of the merging process: shock structure and strength, observational signatures of the dynamical state, effects on the mass determination, turbulence and the evolution of the X-ray luminosity and the magnetic field. In this article I review the results obtained from various simulations over the last years.

The Far Ultraviolet Spectroscopic Explorer (FUSE) provides high-resolution spectroscopy at far ultraviolet (FUV) wavelengths (905–1187Å) of many astronomical objects in order to address fundamental questions related to the origin of the universe. FUSE, a cooperative project of the United States, Canada, and France, was launched in June 1999 for a three-year primary mission. The instrument sensitivity permits studies of many extragalactic sources at high spectral resolution. The key science drivers for the mission design are absorption-line spectroscopy of the ISM and IGM to investigate D/H, O VI, and molecular hydrogen abundances and distribution in the Galaxy and beyond to z ~ 0.3. Most of the observing time is available to Guest Investigators. This Joint Discussion summarizes some of the scientific results determined primarily from the first several months of FUSE observations.

Abundances of ammonia, hydrogen sulfide, water, methane and other hydrocarbons, noble gases and their isotopes, etc. were measured for the first time to the 22 bar level. The ratios of the heavy elements to hydrogen were found to be enriched by a factor of 2-3 relative to solar, implying a large influx of cold planetesimals into Jupiter.

The Galileo spacecraft’s Solid State Imager (SSI) has been returning mosaics of Jupiter since 1996. The combination of high spatial resolution, broad spectral range, and short mosaic time steps has revealed a dynamic, vertically extended cloud structure not detectable by Voyager. These data have stimulated new analyses of major features such as zonal jets, the Great Red Spot, White Ovals, and the Galileo Probe entry site. Near-infrared images have provided fundamental constraints on the vertical structure of clouds and hazes, including the first imaging of a water cloud. Results from night side imaging include an extensive search for lightning, the first matching of lightning events to day side storm clouds, and the first spectral and spatial measurements of visible-wavelength auroral phenomena (not discussed here, see Vasavada et al. 2000). The identification of several tall, energetic storm systems at specific latitudes has led to new ideas about the role of moist convection in Jupiter’s atmospheric energetics.

Jovian auroral emissions are observed at infrared, visible, ultraviolet, and x-ray wavelengths. As at Earth, pitch-angle scattering of energetic particles into the atmospheric loss cone and the acceleration of current-carrying electrons in field-aligned currents both play a role in exciting the auroral emissions. The x-ray aurora is believed to result principally from heavy ion precipitation, while the ultraviolet aurora is produced predominantly by precipitating energetic electrons. The magnetospheric processes responsible for the aurora are driven primarily by planetary rotation. Acceleration of Iogenic plasma by rotationally-induced electric fields results in both the formation of the energetic ions that are scattered and the formation of strong, field-aligned currents that communicate the torques from the ionosphere. In addition to rotation-driven processes, solar-wind-modulated processes in the outer magnetosphere may lead to highly, time-dependent acceleration and thus also contribute to jovian auroral activity. Observational evidence for both sources will be presented. See Waite et al. (2001, Nat., 410, 787).