2,036 research outputs found
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
Recommended from our members
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 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
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