Shock waves in merging galaxy clusters

Shock waves in merging galaxy clusters

Ji-Hoon Ha (UNIST, Korea)

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Dongsu Ryu (UNIST & KASI, Korea) Hyesung Kang (PNU, Korea)

KNAG meeting – Feb 17, 2017

Large Scale Structure of the Universe

(credit: University of Chicago)

Large Scale Structure formation >> Gravitational Collapse..!

2/25 KNAG meeting – Feb 17, 2017

Box size: 43Mpc/h

Large Scale Structure of the Universe

cluster

filament

sheet


(1) External shock >> Nonlinear structure! (2) Internal shock >> Bounded by external shock -Infall shock: infalling gas from WHIM (filament structure) to ICM (cluster of galaxies) >> outskirts of galaxy cluster -Turbulence shock: turbulent flow motion!

-Merger shock: two sub-clumps merging!

(Ryu, D. et al., ApJ 2003) Cosmological Shock

-Cosmological shocks result from the hierarchical formation of large scale structure of the universe. They can be classified into External shock and Internal shock.

(F. Miniati et al. ApJ 2000)

(1<Ms<10) (-9<log Lx<4)

10 erg/s 44 (z=0.25)

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Box size: 50Mpc/h

Statistics of cosmological shocks

-Internal shocks are energetically more important than external shocks.

-External shocks are more common than internal shocks. Shock frequency

Kinetic energy flux

(Ryu, D. et al., ApJ 2003)


Major merger? - Major merger indicates merger with two clusters with comparable masses. - Major merger is the most energetic event in the universe. - Numerous shocks are generated through merger and they dissipate ergs on time-scales of 1 to 2Gyr. >> good X-ray emitting sources.

(Hoeft et al. 2008)

Box size: 6Mpc/h

1<Ms<10 -9<log Lx<4

(Ha, J., Ryu, D., & Kang, H. 2017, in preparation)


6463 1010 −

10 erg/s 44

Internal shocks in merging galaxy cluster X-ray emissivity Kinetic energy flux

144

31 10

21 −⋅≥= ∑ sergvF

sskin ρ

32−≈sM-Merger related shocks dissipate lots of kinetic energy flux.

-Kinetic energy flux contributes to gas thermalization and acceleration of cosmic ray particles.

214031 )(10

21 −− ⋅⋅≥= Mpcsergvf skin ρ

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shock

(shock rest frame)

(upstream) (downstream)

1u 2u- Alfven waves in a converging flow act as kind of converging mirror.

- Particles are scattered by waves and they cross shock several times. ->> they gain nonthermal energy!!

uu

pp ∆≈

∆particle

Cosmic ray acceleration in merging galaxy cluster

<Diffusive Shock Acceleration model>


(e.g. Kang & Ryu 2013)

14210 −⋅≥= sergFF kinCR η

X-ray emissivity CR energy flux

)32(01.0 −≈≈ sMη-Merger related internal shocks play an important role to accelerate cosmic ray particles.

Cosmic ray acceleration in merging galaxy cluster

2138 )(10 −− ⋅⋅≥ MpcsergfCR

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(Kang & Ryu 2013) (Ha, J., Ryu, D., & Kang, H. 2017, in preparation)

Shocks with 1<Ms<7

1st CHEA Workshop

X-ray Emissivity with -5<log Lx<5

Box size: 6Mpc/h


(Sample information: Tx~5keV, Mass ratio~2)

Major merger– 3d movie

10 erg/s 44


- ΛCDM cosmology : ΩΛ = 0.73, ΩDM = 0.27, Ωgas = 0.043, h=0.7, σ8 = 1.05 - no gas cooling, no heating, no feedbacks

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Box size: 4Mpc/h

Equator shock >> perpendicular to the merger axis Axis shock >> along the merger axis

Merger shocks? (Ha, J., Ryu, D., & Kang, H. 2017, in preparation)


Major merger and merger shocks

merger axis

massive clump

light clump

equator shocks axis shock toward

light clump

axis shock toward massive clump

(1) (2) (3)

-Equator shock launches first, and axis shock follows.


Merger at this moment!


Time evolution of merger shocks

45=θ


1<Ms<10

axis shock toward light clump

equator shocks

axis shock toward massive clump


θθθ

θ

(5 merging galaxy clusters with Tx~5keV and mass ratio~2)

Time evolution of merger shocks (Ha, J., Ryu, D., & Kang, H. 2017, in preparation)

Average Mach number

2140 )(10 −− ⋅⋅ Mpcserg

skm /

Average shock velocity

Kinetic energy flux per shock surfaces

Cosmic energy flux per shock surfaces

2140 )(10 −− ⋅⋅ Mpcserg

)(Gyrtt i− )(Gyrtt i−

Shock distance

Mpc

- Each of shocks in the outskirts of cluster dissipates low kinetic energy but they are important in cosmic ray acceleration.

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- Equator shock is stronger than axis shock in light clump and axis shock in massive clump but is less energetic than axis shock.

ds~1-1.7Mpc > 0.5Rvir

)(Gyrtt i−


Merger shocks and radio relics (Ha, J., Ryu, D., & Kang, H. 2017, in preparation)

Sausage relic in the CIZA J2242.8+5301

(van Wereen et al. 2010)


Toothbrush relic in the 1RXS J0603.3+4214

(MCR~3, ds~1-2Mpc, z~0.05-0.3)

(Mradio~2.9, ds~1.5Mpc, z~0.188)

(Mradio~2.8, ds~1.1Mpc, z~0.225)

Most efficient acceleration of cosmic rays!

Merger shocks could be detected radio shocks.

- Radio observation is related to acceleration of cosmic rays (nonthermal process). -Merger shocks with Mradio~3 could be detected in radio observations.

(Stroe et al. 2014)



14010 −⋅ serg

Mpc


Merger shocks and X-ray Observation

- Xray observation is related to gas thermalization at shock surface. - Merger shocks with MX-ray~2.5 could be detected in X-ray observations.

The kinetic energy flux peak at t-ti~1Gyr

Merger shocks could be detected X-ray shocks.

(Mkin~2.5, ds~1-2Mpc, z~0.05-0.3)


1E0657-56 (Bullet cluster)

(Markevitch et al. 2002

(MX-ray~2-3, ds~1Mpc, z~0.3) The galaxy cluster around 3C 438

(Emery et al. 2017)

(MX-ray~2.3, ds~0.8Mpc, z~0.29) Shock front

Cold front


14010 −⋅ serg

Mpc


Cold front in merging galaxy cluster

Shock front

Cold front

(Emery et al. 2017)

The galaxy cluster around 3C 438

-Shock front: defined as both temperature and gas density are increased. -Cold front: defined as the discontinuity that temperature is decreased and gas density is increased.

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Formation of cold front (Bourdin et al. 2013)

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-Before merger, hot gases in converge to center of cluster.

-Shocked gases are squeezed and they are flowing outside.

- Hot gas and clump core are separated and cold front can be formed.

-9<log Lx<4 4<log T<8.5

Toy model from A521

Formation of cold front – simulated cluster (Ha, J., Ryu, D., & Kang, H. 2017, in preparation)

- At merger (z = 0.36), hot gases are compressed at merging cluster center. - Densest subclump core pushes shocked gas in interaction region and hot gas is flowing with low velocity around the merging region without penetrating the massive subcluster core boundary and cold gas converges to the center of the merging cluster. 19/25

Dark Matter in merging galaxy cluster Markevitch et al.

Clowe et al. Dark matter X-ray

1E0657-56 (Bullet cluster)


Galaxy cluster

Galaxy cluster

Dark Matter in merging galaxy cluster (Ha, J., Ryu, D., & Kang, H. 2017, in preparation)

(Sample information: Tx~5keV, Mass ratio~2)

Box size: 6Mpc/h

30001 ≤≤DM

DM

ρρ X-ray Emissivity with -5<log Lx<5

10 erg/s 44


Dark Matter in merging galaxy cluster (Ha, J., Ryu, D., & Kang, H. 2017, in preparation)

Box size: 4Mpc/h >> At merging phase, two dark matter clumps do not interact each other.


Dark Matter & cold front (Ha, J., Ryu, D., & Kang, H. 2017, in preparation)

- Dark matter distribution makes gravitational potential and cold gases are trapped at the center of merging cluster. Hence, the densest clump core and gas in interaction region are separated and a cold front can be formed.


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Summary - Merger shock can be classified into two types. Equator shock is stronger than axis shock but is less energetic than axis shock.

- Axis shock in massive clump is weaker than other types of merger shock but is the most energetic. Hence, energetic shock in massive clump can be observed in X-ray (MX-ray~2.5) and radio (Mradio~3) observations at the outskirts of galaxy clusters (ds~1-2 Mpc~0.5Rvir – 1Rvir) and z<0.3.

- A cold front is formed by steep gradients of temperature & gas density.


- Dark matter distribution in merging galaxy cluster is related to cold front formation.

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Thank you!


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Shock waves in merging galaxy clusters