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RE: Coma Cluster Galaxies
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Title: A particle acceleration site in the Coma cluster?
Authors: D. Eckert, N. Produit, A. Neronov, T. J.-L. Courvoisier

We present the results of a deep (1.1 Ms) observation of the Coma cluster of galaxies in the 18-30 keV band with the IBIS/ISGRI imager on board the INTEGRAL satellite. We show that the source extension in the North-East to South-West (SW) direction (~ 17') significantly exceeds the size of the point spread function of ISGRI, and that the centroid of the image of the source in the 18-30 keV band is displaced in the SW direction compared to the centroid in the 1-10 keV band. To test the nature of the SW extension we fit the data assuming different models of source morphology. The best fit is achieved with a diffuse source of elliptical shape, although an acceptable fit can be achieved assuming an additional point source SW of the cluster core. In the case of an elliptical source, the direction of extension of the source coincides with the direction toward the subcluster falling onto the Coma cluster. If the SW excess is due to the presence of a point source with a hard spectrum, we show that there is no obvious X-ray counterpart for this additional source, and that the closest X-ray source is the quasar EXO 1256+281, which is located 6.1' from the centroid of the excess. Finally, we show that the hard X-ray emission coincides with the 1.4 GHz radio emission, which suggests that the hard X-ray emission comes from the same population of electrons that is responsible for radio haloes through synchrotron emission.

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Title: The Mass Of The Coma Cluster From Weak Lensing In The Sloan Digital Sky Survey
Authors: Jeffrey M. Kubo, Albert Stebbins, James Annis, Ian P. Dell'Antonio, Huan Lin, Hossein Khiabanian, Joshua A. Frieman

We present a weak lensing analysis of the Coma Cluster using the Sloan Digital Sky Survey (SDSS) Data Release Five. Complete imaging of a ~ 200 square degree region is used to measure the tangential shear of this cluster. The shear is fit to an NFW model and we find a virial radius of r_{200}=1.99_{-0.22}^{+0.21}h^{-1}Mpc which corresponds to a virial mass of M_{200}=1.88_{-0.56}^{+0.65}\times10^{15}h^{-1} solar masses.
We additionally compare our weak lensing measurement to the virial mass derived using dynamical techniques, and find they are in agreement. This is the lowest redshift, largest angle weak lensing measurement of an individual cluster to date.

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Giant space cloud
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An enormous cloud of roiling plasma in space may be drawing its energy from black holes, new observations suggest. Such clouds might be sources for the mysterious particles that occasionally crash into Earth's atmosphere at ultra-high speed.
Plasma is a form of matter in which electrons have been ripped from their atomic nuclei, leaving behind a cloud of charged particles. Astronomers can detect plasma as a result of the radio waves emitted by free electrons when they interact with magnetic fields in their environment.
But most radio observations focus on small patches of sky, so they cannot detect very large structures. The newly discovered plasma cloud was discovered in a survey designed to overcome that problem.
Philipp Kronberg of the Los Alamos National Laboratory in New Mexico, US, led a team that used the Arecibo Observatory in Puerto Rico (facing potential closure) and the Dominion Radio Astrophysical Observatory in Penticton, Canada. The combined observations are very sensitive to faint sources over a very large patch of sky equivalent to the width of 16 Full Moons laid side by side.
The researchers discovered a cloud of plasma about 8 million light years across, or 80 times the width of our galaxy, the Milky Way. It is so huge that it appears five times as large as the Full Moon, even though it is millions of light years away.
If humans could see radio waves, the cloud would look like a large, faint blob.

plasma1
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A giant plasma cloud appears as an extended blue blob to the right of the red patch at centre, which is the Coma cluster of galaxies. Galaxies suspected of harbouring supermassive black holes are marked as numbered yellow ovals
Credit Philipp Kronberg et al/LANL/Arecibo Observatory/DRAO


"You wouldn't need the magnification of a telescope to see it at all although you would need radio eyes" - Philipp Kronberg .

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Coma Cluster
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Title: Warm-Hot Intergalactic Medium Associated with the Coma Cluster
Authors: Yoh Takei (1), J. Patrick Henry (2), Alexis Finoguenov (3), Kazuhisa Mitsuda (1), Takayuki Tamura (1), Ryuichi Fujimoto (1), Ulrich G. Briel (3) ((1) ISAS/JAXA, (2) U. Hawaii, (3) MPE)

We present our XMM-Newton RGS observations of X Comae, an AGN behind the Coma cluster. We detect absorption by NeIX and OVIII at the redshift of Coma with an equivalent width of 3.31.8 eV and 1.71.3 eV, respectively (90% confidence errors or 2.3 sigma and 1.9 sigma confidence detections determined from Monte Carlo simulations). The combined significance of both lines is 3.0 sigma, again determined from Monte Carlo simulations. The same observation yields a high statistics EPIC spectrum of the Coma cluster gas at the position of X Comae. We detect emission by NeIX with a flux of 2.51.2 x 10^-8 photons cm^-2 s^-1 arcmin^-2 (90% confidence errors or 3.4 sigma confidence detection). These data permit a number of diagnostics to determine the properties of the material causing the absorption and producing the emission. Although a wide range of properties is permitted, values near the midpoint of the range are T = 4 x 10^6 K, n_H = 6 x 10^-6 cm^-3 corresponding to an overdensity with respect to the mean of 32, line of sight path length through it 41 Z/Zsolar^-1 Mpc where Z/Zsolar is the neon metallicity relative to solar. All of these properties are what has been predicted of the warm-hot intergalactic medium (WHIM), so we conclude that we have detected the WHIM associated with the Coma cluster.

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Coma Cluster Galaxies
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Title: Chandra X-ray Observations of Galaxies in an Off-Centre Region of the Coma Cluster
Authors: A.E. Hornschemeier, B. Mobasher, D.M. Alexander, F.E. Bauer, M.W. Bautz, D. Hammer, B.M. Poggianti

Researchers have performed a pilot Chandra X-ray telescope survey of an off-centre region of the Coma cluster to explore the X-ray properties and Luminosity Function of normal galaxies. They present the results on 13 Chandra-detected galaxies with optical photometric matches, including four spectroscopically-confirmed Coma-member galaxies. All seven spectroscopically confirmed giant Coma galaxies in this field have detections or limits consistent with low X-ray to optical flux ratios (fX/fR < 10^-3).
They do not have sufficient numbers of X-ray detected galaxies to directly measure the galaxy X-ray Luminosity Function (XLF). However, since they have a well-measured optical LF, they took this low X-ray to optical flux ratio for the 7 spectroscopically confirmed galaxies to translate the optical LF to an XLF.
They find good agreement with Finoguenov et al. (2004), indicating that the X-ray emission per unit optical flux per galaxy is suppressed in clusters of galaxies, but extends this work to a specific off-centre environment in the Coma cluster. Finally, They report the discovery of a region of diffuse X-ray flux that might correspond to a small group interacting with the Coma Intra-Cluster Medium (ICM).

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