36,069 research outputs found
Adaptive binning of X-ray galaxy cluster images
We present a simple method for adaptively binning the pixels in an image. The
algorithm groups pixels into bins of size such that the fractional error on the
photon count in a bin is less than or equal to a threshold value, and the size
of the bin is as small as possible. The process is particularly useful for
generating surface brightness and colour maps, with clearly defined error maps,
from images with a large dynamic range of counts, for example X-ray images of
galaxy clusters. We demonstrate the method in application to data from Chandra
ACIS-S and ACIS-I observations of the Perseus cluster of galaxies. We use the
algorithm to create intensity maps, and colour images which show the relative
X-ray intensities in different bands. The colour maps can later be converted,
through spectral models, into maps of physical parameters, such as temperature,
column density, etc. The adaptive binning algorithm is applicable to a wide
range of data, from observations or numerical simulations, and is not limited
to two-dimensional data.Comment: 8 pages, 12 figures, accepted by MNRAS (includes changes suggested by
referee), high resolution version at
http://www-xray.ast.cam.ac.uk/~jss/adbin
Isothermal shocks in Abell 2199 and 2A 0335+096?
We report on a partially circular X-ray surface brightness discontinuity
found at about 55 kpc from the centre of Abell 2199 with Chandra X-ray
observatory observations. Unlike cold fronts found in other clusters, the
feature shows no significant temperature change across it but has an apparent
density jump. We therefore identify it as a weak isothermal shock associated
with the central AGN and the inflation of its radio bubbles, as found in the
Perseus cluster. We examine a similar feature at 40 kpc radius found by
Mazzotta et al in 2A 0335+096, and conclude that it too may be an isothermal
shock. The change in density if these are shocks implies a Mach number of ~1.5.
If the isothermal nature of these features is confirmed by deeper observations,
the implication is that such shocks are common in clusters of galaxies, and are
an important mechanism for the transport of energy from a central supermassive
black hole into the cluster core.Comment: 5 pages, accepted by MNRAS, includes minor changes suggested by
refere
A deeper X-ray study of the core of the Perseus galaxy cluster: the power of sound waves and the distribution of metals and cosmic rays
We make a further study of the very deep Chandra observation of the X-ray
brightest galaxy cluster, A426 in Perseus. We examine the radial distribution
of energy flux inferred by the quasi-concentric ripples in surface brightness,
assuming they are due to sound waves, and show that it is a significant
fraction of the energy lost by radiative cooling within the inner 75-100 kpc,
where the cooling time is 4-5 Gyr, respectively. The wave flux decreases
outward with radius, consistent with energy being dissipated. Some newly
discovered large ripples beyond 100 kpc, and a possible intact bubble at 170
kpc radius, may indicate a larger level of activity by the nucleus a few 100
Myr ago. The distribution of metals in the intracluster gas peaks at a radius
of about 40 kpc and is significantly clumpy on scales of 5 kpc. The temperature
distribution of the soft X-ray filaments and the hard X-ray emission component
found within the inner 50 kpc are analysed in detail. The pressure due to the
nonthermal electrons, responsible for a spectral component interpreted as
inverse Compton emission, is high within 40 kpc of the centre and boosts the
power in sound waves there; it drops steeply beyond 40 kpc. We find no thermal
emission from the radio bubbles; in order for any thermal gas to have a filling
factor within the bubbles exceeding 50 per cent, the temperature of that gas
has to exceed 50 keV.Comment: Accepted by MNRAS. Now includes evidence for further ancient bubble
at 170 kpc radius, and minor changes suggested by referee. A version with
good quality figures is available from
http://www-xray.ast.cam.ac.uk/papers/perdetail2.pd
Large scale gas sloshing out to half the virial radius in the strongest cool core REXCESS galaxy cluster, RXJ2014.8-2430
We search the cool core galaxy clusters in the REXCESS sample for evidence of
large scale gas sloshing, and find clear evidence for sloshing in
RXJ2014.8-2430, the strongest cool core cluster in the REXCESS cluster sample.
The residuals of the surface brightness distribution from the azimuthal average
for RXJ2014 show a prominent swirling excess feature extending out to an abrupt
surface brightness discontinuity at 800 kpc from the cluster core (half the
virial radius) to the south, which the XMM-Newton observations confirm to be
cold, low entropy gas. The gas temperature is significantly higher outside this
southern surface brightness discontinuity, indicating that this is a cold front
800 kpc from the cluster core. Chandra observations of the central 200 kpc show
two clear younger cold fronts on opposite sides of the cluster. The scenario
appears qualitatively consistent with simulations of gas sloshing due to minor
mergers which raise cold, low entropy gas from the core to higher radius,
resulting in a swirling distribution of opposing cold fronts at increasing
radii. However the scale of the observed sloshing is much larger than that
which has been simulated at present, and is similar to the large scale sloshing
recently observed in the Perseus cluster and Abell 2142.Comment: 5 pages, 5 figures. Accepted for publication in MNRA
What fraction of the density fluctuations in the Perseus cluster core is due to gas sloshing rather than AGN feedback?
Deep Chandra observations of the core of the Perseus cluster show a plethora
of complex structure. It has been found that when the observed density
fluctuations in the intracluster medium are converted into constraints on AGN
induced turbulence, the resulting turbulent heating rates are sufficient to
balance cooling locally throughout the central 220kpc. However while the
signatures of AGN feedback (inflated bubbles) dominate the central 60kpc in
X-ray images, beyond this radius the intracluster medium is increasingly shaped
by the effects of gas sloshing, which can also produce subtle variations in
X-ray surface brightness. We use mock Chandra observations of gas sloshing
simulations to investigate what fraction of the observed density fluctuations
in the core of the Perseus galaxy cluster may originate from sloshing rather
than AGN induced feedback. Outside 60kpc, we find that the observed level of
the density fluctuations is broadly consistent with being produced by sloshing
alone. If this is the case, AGN-generated turbulence is likely to be
insufficient in combating cooling outside 60kpc.Comment: 9 pages, 5 figures, accepted for publication in MNRA
Symbolic Computation of Polynomial Conserved Densities, Generalized Symmetries, and Recursion Operators for Nonlinear Differential-Difference Equations
Algorithms for the symbolic computation of polynomial conserved densities, fluxes, generalized symmetries, and recursion operators for systems of nonlinear differential-difference equations are presented. In the algorithms
we use discrete versions of the Fréchet and variational derivatives, as well as discrete Euler and homotopy operators. The algorithms are illustrated for prototypical nonlinear polynomial lattices, including the Kac-van Moerbeke (Volterra) and Toda lattices. Results are shown for the modified Volterra and Ablowitz-Ladik lattices
An XMM-Newton view of the merging activity in the Centaurus cluster
We report the results of XMM-Newton observations of the regions around the
core of the Centaurus cluster where evidence for merging activity between the
subgroup Cen 45 and the main Centaurus cluster has previously been observed
using ASCA and ROSAT data. We confirm the ASCA findings of a temperature excess
surrounding Cen 45. We find that this temperature excess can be explained using
simple shock heating given the large line of sight velocity difference between
Cen 45 and the surrounding main Centaurus cluster. We find that there is a
statistically significant excess in metallicity around Cen 45, showing that Cen
45 has managed to retain its gas as it has interacted with the main Centaurus
cluster. There is a pressure excess to the east in the direction of the merger,
and there is also an entropy excess around the central galaxy of Cen 45. The
metallicity between 50-100 kpc to the north of NGC 4696 is higher than to the
south, which may be the result of the asymmetric distribution of metals due to
previous sloshing of the core, or which may be associated with the filamentary
structure we detect between NGC 4696 and NGC 4696B.Comment: 11 pages, 12 figures. Accepted for publication in MNRA
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