1,253 research outputs found
The extreme ultraviolet excess emission in five clusters of galaxies revisited
Evidence for excess extreme ultraviolet (EUV) emission over a tail of X-ray
gas bremsstrahlung emission has been building up recently, but in some cases
remains controversial, mostly due to the moderate quality of the EUV data. In
order to improve the signal to noise ratio in the EUV, we have performed the
wavelet analysis and image reconstructions for five clusters of galaxies
observed both at EUV and X-ray energies with the EUVE and ROSAT satellites
respectively. The profiles of the EUV and X-ray reconstructed images all differ
at a very large confidence level and an EUV excess over a thermal
bremsstrahlung tail is detected in all five clusters (Abell 1795, Abell 2199,
Abell 4059, Coma and Virgo) up to large radii. These results, coupled with
recent XMM-Newton observations, suggest that the EUV excess is probably non
thermal in origin.Comment: accepted for publication in Astronomy & Astrophysics, final versio
XMM-Newton discovery of O VII emission from warm gas in clusters of galaxies
XMM-Newton recently discovered O VII line emission from ~2 million K gas near
the outer parts of several clusters of galaxies. This emission is attributed to
the Warm-Hot Intergalactic Medium. The original sample of clusters studied for
this purpose has been extended and two more clusters with a soft X-ray excess
have been found. We discuss the physical properties of the warm gas, in
particular the density, spatial extent, abundances and temperature.Comment: 8 pages, 3 figures, conference "Soft X-ray emission from clusters of
galaxies and related phenomena", ed. R. Lieu, Kluwer, in pres
On the absence of gravitational lensing of the cosmic microwave background
The magnification of distant sources by mass clumps at lower ()
redshifts is calculated analytically. The clumps are initially assumed to be
galaxy group isothermal spheres with properties inferred from an extensive
survey. The average effect, which includes strong lensing, is exactly
counteracted by the beam divergence in between clumps (more precisely, the
average reciprocal magnification cancels the inverse Dyer-Roeder
demagnification). This conclusion is in fact independent of the matter density
function within each clump, and remains valid for arbitrary densities of matter
and dark energy. When tested against the CMB, a rather large lensing induced
{\it dispersion} in the angular size of the primary acoustic peaks of the TT
power spectrum is inconsistent with WMAP observations. The situation is
unchanged by the use of NFW profiles for the density distribution of groups.
Finally, our formulae are applied to an ensemble of NFW mass clumps or
isothermal spheres having the parameters of galaxy {\it clusters}. The acoustic
peak size dispersion remains unobservably large, and is also excluded by WMAP.
For galaxy groups, two possible ways of reconciling with the data are proposed,
both exploiting maximally the uncertainties in our knowledge of group
properties. The same escape routes are not available in the case of clusters,
however, because their properties are well understood. Here we have a more
robust conclusion: neither of the widely accepted models are good description
of clusters, or important elements of physics responsible for shaping zero
curvature space are missing from the standard cosmological model. When all the
effects are accrued, it is difficult to understand how WMAP could reveal no
evidence whatsoever of lensing by groups and clusters.Comment: ApJ v628, pp. 583-593 (August 1, 2005
A massive warm baryonic halo in the Coma cluster
Several deep PSPC observations of the Coma cluster reveal a very large-scale
halo of soft X-ray emission, substantially in excess of the well known
radiation from the hot intra-cluster medium. The excess emission, previously
reported in the central region of the cluster using lower-sensitivity EUVE and
ROSAT data, is now evident out to a radius of 2.6 Mpc, demonstrating that the
soft excess radiation from clusters is a phenomenon of cosmological
significance. The X-ray spectrum at these large radii cannot be modeled
non-thermally, but is consistent with the original scenario of thermal emission
from warm gas at ~ 10^6 K. The mass of the warm gas is on par with that of the
hot X-ray emitting plasma, and significantly more massive if the warm gas
resides in low-density filamentary structures. Thus the data lend vital support
to current theories of cosmic evolution, which predict that at low redshift
\~30-40 % of the baryons reside in warm filaments converging at clusters of
galaxies.Comment: Astrophysical Journal, in pres
On the DM interpretation of the origin of non-thermal phenomena in galaxy clusters
(Abridged) We study the predictions of various annihilating Dark Matter (DM)
models in order to interpret the origin of non-thermal phenomena in galaxy
clusters. We consider three neutralino DM models with light (9 GeV),
intermediate (60 GeV) and high (500 GeV) mass. The secondary particles created
by neutralino annihilation produce a multi-frequency Spectral Energy
Distribution (SED), as well as heating of the intracluster gas, that are tested
against the observations available for the Coma cluster. The DM produced SEDs
are normalized to the Coma radio halo spectrum. We find that it is not possible
to interpret all non-thermal phenomena observed in Coma in terms of DM
annihilation. The DM model with 9 GeV mass produces too small power at all
frequencies, while the DM model with 500 GeV produces a large excess power at
all frequencies. The DM model with 60 GeV and composition is
consistent with the HXR and gamma-ray data but fails to reproduce the EUV and
soft X-ray data. The DM model with 60 GeV and composition is always
below the observed fluxes. The radio halo spectrum of Coma is well fitted only
in the or light and intermediate mass DM models. The heating
produced by DM annihilation in the center of Coma is always larger than the
intracluster gas cooling rate for an NFW DM density profile and it is
substantially smaller than the cooling rate only for a cored DM density profile
in DM model with 9 GeV. We conclude that the possibility of interpreting the
origin of non-thermal phenomena in galaxy clusters with DM annihilation models
requires a low neutralino mass and a cored DM density profile. If we then
consider the multimessenger constraints to the neutralino annihilation
cross-section, it turns out that such scenario would also be excluded unless we
introduce a substantial boost factor due to the presence of DM substructures.Comment: 9 pages, 6 figures, 2 Tables. Submitted to A&
On the absence of shear from perfect Einstein rings and the stability of geometry
Concordance cosmology points to a Universe of zero mean curvature, due to the
inflation mechanism which occurred soon after the Big Bang, while along a
relatively small number of lower redshift light paths where lensing events are
observed, space is positively curved. How do we know that global geometry and
topology are robust rather than in a state of chaos? The phenomenon of cosmic
shear provides an effective way of mapping curvature fluctuations, because it
affects {\it any} light rays whether they intercept mass clumps or not. We
discuss a range of astrophysical applications of the principal manifestation of
shear - the distortion of images. It will be shown that the quickest way of
testing the existence of shear in the near Universe is to look at the shape of
Einstein rings. The fact that most of these rings are circular to a large
extent means, statistically speaking, shear occurs at a much lower level than
the expectation based upon our current understanding of the inhomogeneous
Universe. While inflation may account for the mean geometry, it offers no means
of stabilizing it against the fluctuations caused by non-linear matter clumping
at low redshift. Either this clumping is actually much less severe, or the
physical mechanism responsible for shaping the large scale curvature has been
active not only during the very early epochs, but also at all subsequent times.
Might it be the vital `interface' between expansion on Hubble distances and
gravity on cluster scales and beneath?Comment: 16 pages, 3 figures, 18 equations. ApJ in pres
The temperature structure in the core of Sersic 159-03
We present results from a new 120 ks XMM-Newton observation of the cluster of
galaxies Sersic 159-03. In this paper we focus on the high-resolution X-ray
spectra obtained with the Reflection Grating Spectrometer (RGS). The spectra
allow us to constrain the temperature structure in the core of the cluster and
determine the emission measure distribution as a function of temperature. We
also fit the line widths of mainly oxygen and iron lines.Comment: 7 pages and 4 figures. Contribution to the proceedings of the COSPAR
Scientific Assembly, session E1.2 "Clusters of Galaxies: New Insights from
XMM-Newton, Chandra and INTEGRAL", july 2004, Paris (France). Accepted for
publication in Advances in Space Researc
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