220 research outputs found
A numerical simulation of galaxy subcluster mergers
We present preliminary results of a 3-D numerical simulation of two merging subclusters of galaxies. By self-consistently modelling the intracluster gas and dark matter dynamics, we hope to gain insight as to how the dynamics of both relate to such observables as the cluster x-ray emission, radio source morphology, and velocity dispersions
Kinetic Sunyaev-Zeldovich effect from galaxy cluster rotation
We show how the temperature and the polarisation of the cosmic microwave
background are affected by bulk rotation of clusters of galaxies owing to the
kinetic Sunyaev-Zeldovich effect. The main effects of rotation are (i) a shift
of the position of the peak of the temperature fluctuation relative to the
center of the cluster by a few percent of the core radius and (ii) a tilt of
the direction of the plane of linear polarisation by several degrees.Comment: 9 pages, 4 figures, submitted A&
Evolution of shocks and turbulence in major cluster mergers
We performed a set of cosmological simulations of major mergers in galaxy
clusters to study the evolution of merger shocks and the subsequent injection
of turbulence in the post-shock region and in the intra-cluster medium (ICM).
The computations were done with the grid-based, adaptive mesh refinement hydro
code Enzo, using an especially designed refinement criteria for refining
turbulent flows in the vicinity of shocks. A substantial amount of turbulence
energy is injected in the ICM due to major merger. Our simulations show that
the shock launched after a major merger develops an ellipsoidal shape and gets
broken by the interaction with the filamentary cosmic web around the merging
cluster. The size of the post-shock region along the direction of shock
propagation is about 300 kpc h^-1, and the turbulent velocity dispersion in
this region is larger than 100 km s^-1. Scaling analysis of the turbulence
energy with the cluster mass within our cluster sample is consistent with
M^(5/3), i.e. the scaling law for the thermal energy in the self-similar
cluster model. This clearly indicates the close relation between virialization
and injection of turbulence in the cluster evolution. We found that the ratio
of the turbulent to total pressure in the cluster core within 2 Gyr after the
major merger is larger than 10%, and it takes about 4 Gyr to get relaxed, which
is substantially longer than typically assumed in the turbulent re-acceleration
models, invoked to explain the statistics of observed radio halos. Striking
similarities in the morphology and other physical parameters between our
simulations and the "symmetrical radio relics" found at the periphery of the
merging cluster A3376 are finally discussed. In particular, the interaction
between the merger shock and the filaments surrounding the cluster could
explain the presence of "notch-like" features at the edges of the double
relics.Comment: 16 pages, 19 figures, Published in Astrophysical Journal (online) and
printed version will be published on 1st January, 201
A2111: A z=0.23 Butcher-Oemler Cluster with a Non-isothermal Atmosphere and Normal Metallicity
We report results from an X-ray study of the Abell 2111 galaxy cluster using
the Advanced Satellite for Astrophysics and Cosmology ASCA and the ROSAT
Position Sensitive Proportional Counter (PSPC). By correcting for the
energy-dependent point-spread function of the ASCA instruments, we have
examined the temperature structure of the cluster. The cluster's core within 3'
is found to have a temperature of 6.46+-0.87 keV, significantly higher than
3.10+-1.19 keV in the surrounding region of r = 3 - 6'. This radially
decreasing temperature structure can be parameterized by a polytropic index of
1.45. The X-ray morphology of the cluster appears elongated
and clumpy on scales 1'. These results, together with earlier {\it ROSAT}
and optical studies which revealed that the X-ray centroid and ellipticity of
A2111 shift with spatial scale, are consistent with the hypothesis that the
cluster is a dynamically young system. Most likely, the cluster has recently
undergone a merger, which may also be responsible for the high fraction of blue
galaxies observed in the cluster. Alternatively, the temperature structure may
also be due to the gravitational potential of the cluster. We have further
measured the emission weighted abundance of the X-ray-emitting intracluster
medium as 0.250.14 solar. This value is similar to those of nearby
clusters which do not show a large blue galaxy fraction, indicating that star
formation in disk galaxies and subsequent loss to the medium do not drastically
alter the average abundance of a cluster. This is consistent with recent
results which indicate that cluster abundances have remained constant since at
least z ~ 0.3.Comment: accepted by MNRA
Numerical models of jet disruption in cluster cooling flows
We present a coherent picture for the formation of the observed diverse radio morphological structures in dominant cluster galaxies based on the jet Mach number. Realistic, supersonic, steady-state cooling flow atmospheres are evolved numerically and then used as the ambient medium through which jets of various properties are propagated. Low Mach number jets effectively stagnate due to the ram pressure of the cooling flow atmosphere while medium Mach number jets become unstable and disrupt in the cooling flow to form amorphous structures. High Mach number jets manage to avoid disruption and are able to propagate through the cooling flow
RXTE Hard X-ray Observation of A754: Constraining the Hottest Temperature Component and the Intracluster Magnetic Field
Abell 754, a cluster undergoing merging, was observed in hard X-rays with the
Rossi X-ray Timing Explorer (RXTE) in order to constrain its hottest
temperature component and search for evidence of nonthermal emission.
Simultaneous modeling of RXTE data and those taken with previous missions
yields an average intracluster temperature of keV in the 1-50 keV
energy band. A multi-temperature component model derived from numerical
simulations of the evolution of a cluster undergoing a merger produces similar
quality of fit, indicating that the emission measure from the very hot gas
component is sufficiently small that it renders the two models
indistinguishable. No significant nonthermal emission was detected. However,
our observations set an upper limit of
(90% confidence limit) to the nonthermal emission flux at 20 keV. Combining
this result with the radio synchrotron emission flux we find a lower limit of
0.2 G for the intracluster magnetic field. We discuss the implications of
our results for the theories of magnetic field amplifications in cluster
mergers.Comment: Accepted for Publication in the Astrophysical Journal, 22 pages, 5
figure
Hydrodynamic simulations of merging clusters of galaxies
We present the results of high-resolution AP3M+SPH simulations of merging clusters of galaxies. We find that the compression and shocking of the core gas during a merger can lead to large increases in bolometric X-ray luminosities and emission-weighted temperatures of clusters. Cooling flows are completely disrupted during equal-mass mergers, with the mass deposition rate dropping to zero as the cores of the clusters collide. The large increase in the cooling time of the core gas strongly suggests that cooling flows will not recover from such a merger within a Hubble time. Mergers with subclumps having one eighth of the mass of the main cluster are also found to disrupt a cooling flow if the merger is head-on. However, in this case the entropy injected into the core gas is rapidly radiated away and the cooling flow restarts within a few Gyr of the merger. Mergers in which the subcluster has an impact parameter of 500 kpc do not disrupt the cooling flow, although the mass deposition rate is reduced by ∼30 per cent. Finally, we find that equal mass, off-centre mergers can effectively mix gas in the cores of clusters, while head on mergers lead to very little mixing. Gas stripped from the outer layers of subclumps results in parts of the outer layers of the main cluster being well mixed, although they have little effect on the gas in the core of the cluster. None of the mergers examined here resulted in the intracluster medium being well mixed globally
A Prediction of Observable Rotation in the ICM of Abell 3266
We present a numerical Hydro+N-body model of A3266 whose X-ray surface
brightness, temperature distribution, and galaxy spatial and velocity
distribution data are consistent with the A3266 data. The model is an old (~3
Gyr), off-axis merger having a mass ratio of ~2.5:1. The less massive
subcluster in the model is moving on a trajectory from southwest to northeast
passing on the western side of the dominant cluster while moving into the plane
of the sky at ~45 degrees. Off-axis mergers such as this one are an effective
mechanism for transferring angular momentum to the intracluster medium (ICM),
making possible a large scale rotation of the ICM. We demonstrate here that the
ICM rotation predicted by our fully 3-dimensional model of A3266 is observable
with current technology. As an example, we present simulated observations
assuming the capabilities of the high resolution X-ray spectrometer (XRS) which
was to have flown on Astro-E.Comment: 9 pages, 7 postscript figures, Fig. 3 and 6 are color postscript,
Accepted for publication in the Astrophysical Journa
The Observational Consequences of Merging Clusters of Galaxies
We present an observational analysis of numerical simulations of galaxy
cluster mergers. We identify several observational signatures of recent merger
activity, and quantitatively assess the uncertainty introduced into cluster
mass estimates when invoking the commonly held assumptions of hydrostatic
equilibrium, virial equilibrium, spherical symmetry and isothermality. We find
that mergers result in multiple X-ray peaks, long-lived elongation of the X-ray
emission as well as isophotal twisting and centroid shifting to a degree
consistent with recent observations. We also find an enlargement of the X-ray
core relative to the dark matter core. Mergers result in non-isothermal
clusters exhibiting observable inhomogeneities in the emission-weighted X-ray
temperature of several keV on linear scales of less than 0.5 Mpc. The resulting
gas dynamics are extremely complex, and we present an example of what might be
observed by a high resolution X-ray spectrograph. We further speculate that the
gas dynamics, via shocks, bulk flows and turbulence, play an important role in
the evolution of cluster galaxies and associated radio sources, particularly
wide-angle tailed (WAT) sources and radio halos. We find that X-ray based by
cluster mass estimates made under equilibrium assumptions can be uncertain 50\%
or more in the first 2 Gyrs after a merger and by up to 25\% after 2 Gyrs
depending on the details of the analysis and projection effects. Uncertainties
can be considerably larger if the temperature is not well constrained.Comment: 42 pages, Latex, 23 postscript figures, Accepted for publication in
Ap
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