Hot Electrons and Cold Photons: Galaxy Clusters and the Sunyaev-Zel'dovich Effect

The hot gas in clusters of galaxies emits thermal bremsstrahlung emission that can be probed directly through measurements in the X-ray band with satellites like ROSAT and ASCA. Another probe of this gas comes from its effect on the cosmic microwave background radiation (CMBR): the hot cluster electrons inverse Compton scatter the CMBR photons and thereby distort the background radiation from its blackbody spectral form. In the last few years, the development of sensitive new instruments for measuring this distortion, called the Sunyaev-Zel'dovich (SZ) effect, has sparked a revolution in the field. Current radio interferometric arrays can now detect and map the SZ effect in even distant (z ~ 1) clusters. It is well known that one of the purposes of conducting such measurements is to determine the Hubble constant. In this review I report on the progress that has been made in this area, quote the current best estimate of Ho from the SZ effect of 8 galaxy clusters (44 - 64 km/s/Mpc +/- 17%), discuss important systematic uncertainties, and highlight what else has been learned about galaxy clusters from these investigations.Comment: 4 pages, including 2 postscript figs, LaTeX. To appear in the proceedings of IAU Symposium 188 "The Hot Universe" (held August 26-30, 1997, Kyoto, Japan

Sliding not sloshing in Abell 3744: the influence of radio galaxies NGC 7018 and 7016 on cluster gas

We present new X-ray (Chandra) and radio (JVLA) observations of the nearby cluster Abell 3744. It hosts two prominent radio galaxies with powers in the range critical for radio-mode feedback. The radio emission from these galaxies terminates in buoyant tendrils reaching the cluster's outer edge, and the radio-emitting plasma clearly influences the cluster's X-ray-emitting atmosphere. The cluster's average gas temperature, of kT=3.5 keV, is high for its bolometric luminosity of 3.2 \times 10^{43} ergs s^{-1}, but the 100 kpc-scale cavity carved out by radio-emitting plasma shows evidence of less than 2 per cent of the excess enthalpy. We suggest instead that a high-velocity encounter with a galaxy group is responsible for dispersing and increasing the entropy of the gas in this non-cool-core cluster. We see no evidence for shocks, or established isobaric gas motions (sloshing), but there is much sub-structure associated with a dynamically active central region that encompasses the brightest radio emission. Gas heating is evident in directions perpendicular to the inferred line of encounter between the infalling group and cluster. The radio-emitting tendrils run along boundaries between gas of different temperature, apparently lubricating the gas flows and inhibiting heat transfer. The first stages of the encounter may have helped trigger the radio galaxies into their current phase of activity, where we see X-rays from the nuclei, jets, and hotspots.Comment: Accepted for publication in ApJ (13 pages, 17 figures

Observational issues in radiometric and interferometric detection and analysis of the Sunyaev-Zel'dovich effects

This review discusses the techniques used in single-dish and interferometric radiometric observations of the Sunyaev-Zel'dovich effects, the pitfalls that arise, the systematic and other sources of error in the data, and the uncertainties in the interpretation of the results.Comment: 46 pages, 23 figures. To appear in Background Microwave Radiation and Intracluster Cosmology, Proceedings of the International School of Physics "Enrico Fermi", Eds. Melchiorri, F. & Rephaeli, Y., 200

How management innovation happens

Management innovation — that is, the implementation of new management practices, processes and structures that represent a significant departure from current norms — has over time dramatically transformed the way many functions and activities work in organizations. Many of the practices, processes and structures that we see in modern business organizations were developed during the last 150 years by the creative efforts of management innovators. Those innovators have included well-known names like Alfred P. Sloan and Frederick Taylor, as well as numerous other unheralded individuals and small groups of people who all sought to improve the internal workings of organizations by trying something new

Redshift and velocity dispersion of the cluster of galaxies around NGC 326

Redshifts of several galaxies thought to be associated with NGC 326 are determined. The results confirm the presence of a cluster and find a mean redshift of z = 0.0477 +/- 0.0007 and a line-of-sight velocity dispersion sigma_{z} = 599 (+230, -110) km/s. The velocity dispersion and previously measured X-ray gas temperature of kT ~ 1.9 keV are consistent with the cluster sigma_{z}/kT relation, and NGC 326 is seen to be a slowly-moving member of the cluster.Comment: 3 pages, to appear in MNRA

The Infrared Jet In 3C66B

We present images of infrared emission from the radio jet in 3C66B. Data at three wavelengths (4.5, 6.75 and 14.5 microns) were obtained using the Infrared Space Observatory. The 6.75 micron image clearly shows an extension aligned with the radio structure. The jet was also detected in the 14.5 micron image, but not at 4.5 micron. The radio-infrared-optical spectrum of the jet can be interpreted as synchrotron emission from a population of electrons with a high-energy break of 4e11 eV. We place upper limits on the IR flux from the radio counter-jet. A symmetrical, relativistically beamed twin-jet structure is consistent with our results if the jets consist of multiple components.Comment: 7 pages, 4 figure

The Sunyaev-Zel'dovich Effect

The Sunyaev-Zel'dovich effect 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 effect provide distinctly different information about cluster properties than X-ray imaging data, while combining X-ray and Sunyaev-Zel'dovich effect data leads to new insights into the structures of cluster atmospheres. The effect 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 effect and collects published results for many clusters, presents the overall conclusions that may be drawn from the detections so far, and discusses the prospects for future research on the Sunyaev-Zel'dovich effects.Comment: 137 pages, 28 figures. LaTeX (aastex macros) plus encapsulated PostScript. To appear in Physics Report

Buoyancy-driven inflow to a relic cold core: the gas belt in radio galaxy 3C 386

We report measurements from an XMM-Newton observation of the low-excitation radio galaxy 3C 386. The study focusses on an X-ray-emitting gas belt, which lies between and orthogonal to the radio lobes of 3C 386 and has a mean temperature of $0.94\pm0.05$ keV, cooler than the extended group atmosphere. The gas in the belt shows temperature structure with material closer to the surrounding medium being hotter than gas closer to the host galaxy. We suggest that this gas belt involves a `buoyancy-driven inflow' of part of the group-gas atmosphere where the buoyant rise of the radio lobes through the ambient medium has directed an inflow towards the relic cold core of the group. Inverse-Compton emission from the radio lobes is detected at a level consistent with a slight suppression of the magnetic field below the equipartition value.Comment: 11 pages, 10 figures, accepted for publication in MNRA

Galaxy gas ejection in radio galaxies: the case of 3C 35

We report results from XMM-Newton and Chandra observations of the nearby (z = 0.067) giant radio galaxy 3C 35. We find evidence for an X-ray emitting gas belt, orthogonal to and lying between the lobes of 3C 35, which we interpret as fossil-group gas driven outwards by the expanding radio lobes. We also detect weak emission from a second, more extended group-type environment, as well as inverse-Compton X-ray emission from the radio lobes. The morphological structure of the radio lobes and gas belt point to co-evolution. Furthermore, the radio source is powerful enough to eject galaxy-scale gas out to distances of 100kpc, and the ages of the two features are comparable (tsynch~140Myr, tbelt~80 Myr). The destruction of 3C 35's atmosphere may offer clues as to how fossil systems are regulated: radio galaxies need to be of power comparable to 3C 35 to displace and regulate fossil-group gas. We discuss the implications of the gas belt in 3C 35 in terms of AGN fuelling and feedback.Comment: 18 pages, accepted to MNRA