Xray and radio connection for merger cluster A548b

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X-ray and radio connection for merger cluster
A548b
Lilia Solovyeva, Jean-Luc Sauvageot,
RomainTeyssier, Sergey Anokhin
CEA/Saclay, SAp
Luigina Feretti
Istituto di Radioastronomia INAF, Bologna, Italy
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Davis et al 1995
Cluster of galaxies A548b
A548b nearby galaxy cluster, z 0.0423
R2001.45Mpc ensemble cluster A548 - near 2
clusters A548a, z 0.0394
A548-2, z 0.0429 gtPossibility of merger
A548b 3 radio relics A B C
Objective

• Combination of X-ray radio optical data
  and simulation
• Dynamical state of A548b.
• To study the thermal-relativistic plasma
  connection by combining radio and X-ray data

Cluster A548 is in a very complex state of
interaction. The presence of relics in A548b
confirm the association between relics and merger
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Result from radio analysis
L.Feretti et al. 2006
Diffuse radio emission demonstrate the existence
of relativistic particles and magnetic fields in
the ICM
VLA observation 1.4, 4.8, 8.4GHz (Very Large
Array)
Information from 1.4GHz 2 diffuse radio sources
in the cluster peripheries AB round
ships size about 300kpc high level of
polarization - 30 spectral index -
(-2/-1) no information from Faraday
rotation 1 diffuse radio source in the cluster
centre -C polarization is 7
first cluster where two radio relics are located
on the same side with respect to the cluster
centre
ATCA observation 1.4, 1.7, 2.5 GHz (Australia
Telescope Compact Array)
Result from high resolution images (Point
sources) The radio point sources are not
associated with diffuse sources
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X-ray analysis - images analysis Position for XMM
observation
Relics - in peripheries of cluster gt difficult
to obtain the X-ray information. gt Deep study in
region between cluster centre and radio
relics gt Offset observation centered onto the
regions between cluster centre and radio relics
A548b was observed 2006 February 17 - 70/64
ksec -MOS, pn For camera MOS1-not CCD6 1arcmin
47kpc
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X-ray analysis - images analysis Surface
brightness profile, ?-model
vignetting correction background J.Nevalainen
(also with bkg D. Lumb) double background
subtraction CXB NXB Arnaud et
al.2002 ?-fit model (-10 first points)
radial SB profile (0.3-4.5keV) chosen sectors gt
to study the connection X-ray /radio relics
gt All bad fit with ?-model very probably merger !
radial SB profiles
N
NE
NW
E
W E N
NW NE
W
S
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X-ray analysis - images analysis 2D??-model
X-ray source? group

• 2D?? analysis gt
• corrected image
• Taking into account the
• vigneting effect
• Modelling and Subtraction of background
• from observations data

• The CXB and NXB component were modelled from
  observation data (including vignetting effect)
• Correction of the gap and point sources
• Subtracted images only MOS2pn

• gt residual after subtraction of 2D ?-model fit
  (6 arcmin)
• similar results with ROSAT data
• gtPerturbation near the center gtmerging!

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X-ray Spectral analysis Mean temperature,
temperature in regions,temperature profile
The spectra in the six concentric annuli up to 12
arcmin, each 2 arcmin
using the MEKAL plasma emission model 3
cameras of XMM
background of J.Nevalainen (also D. Lumb) double
background subtraction abundance fixed
to 0.3 Z?
T mean of cluster 3.4keV Increasing of T before
relic 5 keV !
Shock in 6 arcmin (3.5keV - 5.5keV) before
relics ? To understand better the dynamics gt
Temperature map!
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X-ray Spectral analysis Temperature map
Relic
NE NW N

• Temp. increases in the relic direction
• gt Temperature profiles in each sectors N,W, S,E
• shock just in relics directions!
• Temperature profile in relic directions relics
  A/B - NW/NE

Relic

• To understand better the cluster dynamics
• temperature map
• in square sectors (Mekal, double soubstraction)
• gt
• increasing T - up to 6 keV
• in 6 arcmin /282kpc
• in north direction
• in relics direction
• 8 arcmin / 376kpc
• same results for T map
• were obtained using XWSM
• (X-ray wavelet spectral mapping
• -H. Bourdin 2004)

282kpc
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X-ray analysis. Results Dynamical state A548b
Relics
Shock in T from 3 to 6 keV
lt Simulations Shock in the same direction
perturbation in emissivity
Apparent contradiction between shock and
filaments orientations? Projection Effects
T map
Davis et al. 1995
to understand the dynamics of A548b we need to
understand the geometry gt optics
analysis comparison with simulation
A548a
A548b
effect projection!!!
A548-2
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Optics analysis

• NED database
• optical information
• 193 galaxies velocities with rprojltR200 of A548b

• Velocity distribution of galaxy cluster A548b
• ?V(1 Gauss) 1000km/s
• (similar to cluster _at_7 keV !!)
• 2 gauss fit gt
• 39 galaxies at zlt0.04
• 63 galaxies at z gt0.042

Distribution of galaxies blue probably from
A548a red probably from A548-2
gt If true, then the merger occur nearly
perpendicularly to the plane of the sky
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Comparison with simulation. Cluster 6
To study the dynamical properties of cluster
around the merger
Hydro N-body cosmology simulation using the
RAMSES code (R.Teyssier) a parallel adaptive
mesh refinement code for astrophysical fluid
dynamics Cluster 6 ?m0.3 and ??0.7 T 3.3keV
and R2000.98 Mpc/h , 1.42Mpc just adiabatic
simulation
To study the evolution of the following physical
quantities dark matter density gas
pressure gas density temperature Mach number
We focus on the epoch when two clumps merge
along a large scale filament and consider
different projection axis !
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Comparison with simulation. Cluster 6 Z
projection
T map
Chosen output from simulation Cluster 6 - just
after maximum core collapse (30Myr) result from
average from z projection density
map temperature map relative Mach number map
M(v1-v2)/cs gtconnection with radio data
and particle acceleration (detect strong shocks!)
Shock - similar distance, good Temp. ratio!!! But
note different geometry !
A548b XMM obs
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Comparison with simulation. Cluster 6 Y
projection - to line of observation
T profile
Cluster 6 - just after maximum core collapse
(30Myr) result from average from Y
projection density map temperature map (rapport
de Tmax/TMean mach number map from velocity
M(v1-v2)/cs gtconnection with radio data
-directly shock!
density profile
Shock - similar distance, good Temp. Ratio more
similar geometry

• other outputs from simulation
• gt
• less significantly Temp. Ratio

A548b XMM obs
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Results Discussions
X-ray / radio connection for A548b
X-ray analysis A548b is not in Hydrostatic
Equilibrium T increases nearby the
radio relics position (but significantly before)
perturbation in emissivity near the
relics position Theory wants relics to have
been crossed by the shock wave,
How to reconcile theory with observation
? statistics effect projection theory? Is
the fact that Radio relics lie in the same side
of the cluster center linked with the observed
increase of the Temperature in the same region ?
gt what is the merger collision geometry
? shock wave direction is in contradiction with
filaments direction, gt optics analysis
Galaxies Velocity favours scenario with strong
projection effects. Collision nearly
perpendicular to the plane of the sky Then
material probably come from NorthEast and West
filaments. Relics are observed in same
side due to collision directions and Temp.
increases. Thus, the observations suffer from
strong projection effect
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Results
Projection effect
Comparison with numerical simulation (Hydro
N-body Cosmology Simulation) chose an
output time similar to the observation Just
after maximum core collapse, we have -same T
and density profile in Y proj -similar T1/T2
ratio than observed in A548b Maximum
gradient of the Mach number detected just after
the shock (T M2) From simulation in
different projections, we observed the same shock
in different situations Or
Using projection effect, one can imagine that
the T increase appears nearer to the center than
the relics (even if this is not true in 3D).
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Conclusion
Note how important is the environment (nearby
cluster- filaments) to understand the geometry of
merger and the dynamical history of cluster. To
understand the geometry we need optical analysis
and 3D simulations to disentangle true physical
properties from projection effects. (Need to
obtain better spectral optical data) For more
constraining comparisons with radio data, we
need to add CR mechanism in simulations and not
only adiabatic simulations.
We propose
That A548b is a merger with a collision axis far
from the plan of the sky, with materials coming
from similar directions as the cluster neighbors
(filaments..). In that scheme, the relics could
have been already lightened up by the
shock. Direct signatures onto the X-ray/Radio
connexion have been found , but not very strong
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Thank you for your attention!
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Spectral result from XWSM