Galaxies Cluster formation : Numerical Simulations and XMM

Observations JL Sauvageot*, Elena Belsole*,R.Teyssier*,

Herve Bourdin+

• Service d'Astrophysique CEA-Saclay

+NICE Observatory

Palermo, 2003

I) Simulations of Merging Clusters of galaxies

II) Convolution and Temperature map Reconstruction

III) XMM Observations of A1750, A3921 and A2065

IV) Conclusion

Major mergersQuiet accretion

Two paths for building clusters :Through nearly continuous groups infall mgroup<< MClus

Or by Major Merger MClus1 ~ MClus2

From observations we learn that: Most clusters are accreting smaller clumps at present.3 to15 % of clusters have undergoing a major merger in the last Gyr (at low redshift).

Galaxies Clusters Formation

Cavalie

re e

t al.

I) Mergers in cosmological environment

RAMSES: Teyssier, 2002, A&A,385,337Particle-Mesh Method (N-Body, Dark Matter)Pieceweise Linear Method (Euler Equation, Gas)Adaptive Mesh Refinement

Starting from Initials Density Fluctuations, you could not set where the cluster will form, what are the parameters of the collisions, what is the history of previous events...

Simulation in 2 runs :-1- Box of universe of Lbox=400 h-1 MpcNpart=1283, CDM simulation => ~ 100

clusters-2- Zoom onto one Major Merging Event

(re-play)Same Universe Box with more than 400

000 particles and mesh points within the selected cluster Virial radius.

==> realistic simulation of large scale potential & continuous infall AND high local resolution.

The mesh spacing in the cluster core went down to 6 h-1 kpc, (corresponding to a formal resolution of 655363)

Dar

k M

atte

rG

rid

Spa

cing

Tem

pera

ture

II) Cosmological Simulation as seen through XMM-Newton

From RAMSES Simul., we have ,T for each cell (+x,y,z position)Generation of photons list using Plasma code Database + Monte-CarloUsing XMM Calibration files to emulate the InstrumentThen Comparison between observation and simulations.Cosmological Simulation are much more realistic but : One could not chose the Initial collision parameters.Much more complex initial state of the units due to their own history of merging.

Density (or X-ray Low Energy ) Map : shows gas distribution with limited contrast (even in strong shock case, r/r 4)

Temperature (or Hardness Ratio) Map : Higher Contrast in T, Lifetime up to 6 time longer.

but less direct (and much more difficult to achieve).

From X-rays Observations of Mergers we get :

II) Cluster merging in a realistic Cosmological environment.

X rays(Low Energy) Temperature map

AFTER XMM/EPIC and Tmap Algo.

Temperature Map Computation for X-ray Cluster of Galaxies : H. Bourdin et al. A&A 2003 accepted

Emissivity EM weighted Temp.

BEFORE the instrument simulation.

Com

pressionS

hock

Z=

0.13

Z=

0.09

Z=

0.

IIIa) A1750 XMM Observation

kT map enhancement of T in the interaction region+ History effect

Low Energy [0.3-0.6 keV] imageAdaptatively Smoothed.

1.0 keV 6 keV

z=0.086; 30 ksec GT; Bi-modal structure ; ~1 to 1 mass Collision; Projected Distance between units ~ 1Mpc ; Vredshift~1000 km/skT=2.84+/-0.12 keV

kT=5.12+/-0.7 keV

kT=3.87+/-0.1 keV

30 arcmin ~ 2.6 Mpc

An XMM-Newton Observation of the dynamically active binary cluster A1750 : E.Belsole et al. A&A,2003 submitted

A1750 is a real merger just at the beginning of the event:

Detection of a hotter region in the interaction zone.BUT its 2 sub-units are already NOT relaxed (highly distorted contours+ very complex Temperature Structure)==>A1750 is an observational evidence that Time Interval between collision is (at least sometime) shorter than relaxation time

IIIa) A1750 Conclusions

Comparing projected distance (1Mpc) and Numerical Simulations of major merger units at that distance ==> Real distance between units should be higher==>Strong Projection Effect

~9 Mpc

Rosat PSPC Field

Main Component Spectrum

4.35+/-0.1 keV

B1: Interaction zone Spectrum

5.6+/-0.3 keV

IIIb) A3921 XMM Observation

Z=0.094, 30 ksec GT Observation3 cD galaxiesHighly elongated X-ray structure

Adaptatively smoothed Low Energy Image

IIIb) A3921 XMM Observation

3.00 6.00

All galaxies used to build the map are at zA3921 with mGal<22.Galaxies are less collisional than Gas ==> They better follow the Dark Matter potential.

Optical data from Nice Obs. Collaborators

Temp. Map with adaptative bining Multiscale Temp. Map reconstruction

Galaxies Density map.

IIIb) Idealized 3M/M Simulation of mergerwith a Large Impact Parameter b=5 rs

LX contours onto Temperature map

-0.5 0 1 GyrTime

Density contours onto Dark Matter map

Galaxies Density MapM over 3M collision Ricker&Sarazin2001

A3921 is a complex case of merger:From X-rays : Hotter interaction region NOT orthogonal to the line linking the centers of the sub-units but nearly parallel to it.

From Optical: Velocity information+ Galaxy Density Map

do NOT support the pre-merger view.

Proposed scenario:The small group has already pass through the main cluster with animpact parameter 0

IIIb) A3921 Preliminary Conclusions

IIIc) A2065: a Merger in the compact phase

seen with XMM 30 ksec but Very High Level of Protons ==> very specific treatment==> Model of the protons spectrum and spatial distribution.==> Analysis limited by statistics and confidence but a Shock wave could have been detected on A2065

A2065Low Energy EPIC Map

kT map Simulation

Hardness Ratio Map

+ Surviving Cooling flow ... will be re-observed during AO3

IV)ConclusionsNumerical Simulations seem to agree qualitatively with X-ray

observations of early mergers, BUT detailed quantitative comparisons still need to be

done.-A1750 seems to be an early merger bi-modal system. But its

2 sub-units are already not relaxed due to their own history.

-A3921 is much more complex :it may be an off-axis 3/1 Mass late merger. (detailed optical

vs X-ray comparison to be done)-A2065 really looks like a Compact Post Merger. Better

quality data needed to confirm (XMM-AO3).

To understand the X-rays mergers observations, we definitely need :

Data in Visible and Numerical Simulations

The Observable :

Image represent the emission weighted Temperature

Contours are the X-ray Luminosity

-0.5 0 1 2 3.5 Gyr

B=0

B=2 rs

B=5 rs

Ia)Idealized Simulation (Ricker&Sarazin2001)Impact

Parameter

Time

Im(2.5-6.5 keV)

HR Map = __________________

Im(0.3-0.9 keV)

A3921 Hardness Ratio Map